Failover for High Availability

This chapter describes how to configure Active/Standby or Active/Active failover to accomplish high availability of the ASA.

About Failover

Configuring failover requires two identical ASAs connected to each other through a dedicated failover link and, optionally, a state link. The health of the active units and interfaces is monitored to determine whether they meet the specific failover conditions. If those conditions are met, failover occurs.

Failover Modes

The ASA supports two failover modes, Active/Active failover and Active/Standby failover. Each failover mode has its own method for determining and performing failover.

  • In Active/Standby failover, one device functions as the Active unit and passes traffic. The second device, designated as the Standby unit, does not actively pass traffic. When a failover occurs, the Active unit fails over to the Standby unit, which then becomes Active. You can use Active/Standby failover for ASAs in single or multiple context mode.

  • In an Active/Active failover configuration, both ASAs can pass network traffic. Active/Active failover is only available to ASAs in multiple context mode. In Active/Active failover, you divide the security contexts on the ASA into 2 failover groups. A failover group is simply a logical group of one or more security contexts. One group is assigned to be Active on the primary ASA, and the other group is assigned to be active on the Secondary ASA. When a failover occurs, it occurs at the failover group level.

Both failover modes support stateful or stateless failover.

Failover System Requirements

This section describes the hardware, software, and license requirements for ASAs in a Failover configuration.

Hardware Requirements

The two units in a Failover configuration must:

  • Be the same model. In addition, for container instances, they must use the same resource profile attributes.

    For the Firepower 9300, High Availability is only supported between same-type modules; but the two chassis can include mixed modules. For example, each chassis has an SM-56, SM-48, and SM-40. You can create High Availability pairs between the SM-56 modules, between the SM-48 modules, and between the SM-40 modules.

  • Have the same number and types of interfaces.

    For the Firepower 2100 in Platform mode and Firepower 4100/9300 chassis, all interfaces must be preconfigured in FXOS identically before you enable Failover. If you change the interfaces after you enable Failover, make the interface changes in FXOS on the Standby unit, and then make the same changes on the Active unit. If you remove an interface in FXOS (for example, if you remove a network module, remove an EtherChannel, or reassign an interface to an EtherChannel), then the ASA configuration retains the original commands so that you can make any necessary adjustments; removing an interface from the configuration can have wide effects. You can manually remove the old interface configuration in the ASA OS.

  • Have the same modules installed (if any).

  • Have the same RAM installed.

If you are using units with different flash memory sizes in your Failover configuration, make sure the unit with the smaller flash memory has enough space to accommodate the software image files and the configuration files. If it does not, configuration synchronization from the unit with the larger flash memory to the unit with the smaller flash memory will fail.

Software Requirements

The two units in a Failover configuration must:

  • Be in the same context mode (single or multiple).

  • For single mode: Be in the same firewall mode (routed or transparent).

    In multiple context mode, the firewall mode is set at the context-level, and you can use mixed modes.

  • Have the same major (first number) and minor (second number) software version. However, you can temporarily use different versions of the software during an upgrade process; for example, you can upgrade one unit from Version 8.3(1) to Version 8.3(2) and have failover remain active. We recommend upgrading both units to the same version to ensure long-term compatibility.

  • Have the same Secure Client images. If the failover pair has mismatched images when a hitless upgrade is performed, then the clientless SSL VPN connection terminates in the final reboot step of the upgrade process, the database shows an orphaned session, and the IP pool shows that the IP address assigned to the client is “in use.”

  • Be in the same FIPS mode.

  • (Firepower 4100/9300) Have the same flow offload mode, either both enabled or both disabled.

License Requirements

The two units in a failover configuration do not need to have identical licenses; the licenses combine to make a failover cluster license.

Failover and Stateful Failover Links

The failover link and the optional stateful failover link are dedicated connections between the two units. Cisco recommends to use the same interface between two devices in a failover link or a stateful failover link. For example, in a failover link, if you have used eth0 in device 1, use the same interface (eth0) in device 2 as well.


Caution

All information sent over the failover and state links is sent in clear text unless you secure the communication with an IPsec tunnel or a failover key. If the ASA is used to terminate VPN tunnels, this information includes any usernames, passwords and preshared keys used for establishing the tunnels. Transmitting this sensitive data in clear text could pose a significant security risk. We recommend securing the failover communication with an IPsec tunnel or a failover key if you are using the ASA to terminate VPN tunnels.

Failover Link

The two units in a failover pair constantly communicate over a failover link to determine the operating status of each unit.

Failover Link Data

The following information is communicated over the failover link:

  • The unit state (active or standby)

  • Hello messages (keep-alives)

  • Network link status

  • MAC address exchange

  • Configuration replication and synchronization

Interface for the Failover Link

You can use an unused data interface (physical, subinterface, or EtherChannel) as the failover link; however, you cannot specify an interface that is currently configured with a name. The failover link interface is not configured as a normal networking interface; it exists for failover communication only. This interface can only be used for the failover link (and also for the state link). For most models, you cannot use a management interface for failover unless explicitly described below.

The ASA does not support sharing interfaces between user data and the failover link. You also cannot use separate subinterfaces on the same parent for the failover link and for data.

See the following guidelines for the failover link:

  • 5506-X through 5555-X—You cannot use the Management interface as the failover link; you must use a data interface. The only exception is for the 5506H-X, where you can use the management interface as the failover link.

  • 5506H-X—You can use the Management 1/1 interface as the failover link. If you configure it for failover, you must reload the device for the change to take effect. In this case, you cannot also use the ASA Firepower module, because it requires the Management interface for management purposes.

  • Firepower 4100/9300—We recommend that you use a 10 GB data interface for the combined failover and state link. You cannot use the management-type interface for the failover link.

  • All other models—1 GB interface is large enough for a combined failover and state link.

The alternation frequency is equal to the unit hold time (the failover polltime unit command).


Note

If you have a large configuration and a low unit hold time, alternating between the member interfaces can prevent the secondary unit from joining/re-joining. In this case, disable one of the member interfaces until after the secondary unit joins.

For an EtherChannel used as the failover link, to prevent out-of-order packets, only one interface in the EtherChannel is used. If that interface fails, then the next interface in the EtherChannel is used. You cannot alter the EtherChannel configuration while it is in use as a failover link.

Connecting the Failover Link

Connect the failover link in one of the following two ways:

  • Using a switch, with no other device on the same network segment (broadcast domain or VLAN) as the failover interfaces of the ASA.

  • Using an Ethernet cable to connect the units directly, without the need for an external switch.

If you do not use a switch between the units, if the interface fails, the link is brought down on both peers. This condition may hamper troubleshooting efforts because you cannot easily determine which unit has the failed interface and caused the link to come down.

The ASA supports Auto-MDI/MDIX on its copper Ethernet ports, so you can either use a crossover cable or a straight-through cable. If you use a straight-through cable, the interface automatically detects the cable and swaps one of the transmit/receive pairs to MDIX.

Stateful Failover Link

To use Stateful Failover, you must configure a Stateful Failover link (also known as the state link) to pass connection state information.

Shared with the Failover Link

Sharing a failover link is the best way to conserve interfaces. However, you must consider a dedicated interface for the state link and failover link, if you have a large configuration and a high traffic network.

Dedicated Interface

You can use a dedicated data interface (physical or EtherChannel) for the state link. See Interface for the Failover Link for requirements for a dedicated state link, and Connecting the Failover Link for information about connecting the state link as well.

For optimum performance when using long distance failover, the latency for the state link should be less than 10 milliseconds and no more than 250 milliseconds. If latency is more than 10 milliseconds, some performance degradation occurs due to retransmission of failover messages.

Avoiding Interrupted Failover and Data Links

We recommend that failover links and data interfaces travel through different paths to decrease the chance that all interfaces fail at the same time. If the failover link is down, the ASA can use the data interfaces to determine if a failover is required. Subsequently, the failover operation is suspended until the health of the failover link is restored.

See the following connection scenarios to design a resilient failover network.

Scenario 1—Not Recommended

If a single switch or a set of switches are used to connect both failover and data interfaces between two ASAs, then when a switch or inter-switch-link is down, both ASAs become active. Therefore, the following two connection methods shown in the following figures are NOT recommended.

Figure 1. Connecting with a Single Switch—Not Recommended
Figure 2. Connecting with a Double-Switch—Not Recommended
Scenario 2—Recommended

We recommend that failover links NOT use the same switch as the data interfaces. Instead, use a different switch or use a direct cable to connect the failover link, as shown in the following figures.

Figure 3. Connecting with a Different Switch
Figure 4. Connecting with a Cable
Scenario 3—Recommended

If the ASA data interfaces are connected to more than one set of switches, then a failover link can be connected to one of the switches, preferably the switch on the secure (inside) side of network, as shown in the following figure.

Figure 5. Connecting with a Secure Switch

MAC Addresses and IP Addresses in Failover

When you configure your interfaces, you can specify an active IP address and a standby IP address on the same network. Generally, when a failover occurs, the new active unit takes over the active IP addresses and MAC addresses. Because network devices see no change in the MAC to IP address pairing, no ARP entries change or time out anywhere on the network.


Note

Although recommended, the standby address is not required. Without a standby IP address, the active unit cannot perform network tests to check the standby interface health; it can only track the link state. You also cannot connect to the standby unit on that interface for management purposes.

The IP address and MAC address for the state link do not change at failover.

Active/Standby IP Addresses and MAC Addresses

For Active/Standby Failover, see the following for IP address and MAC address usage during a failover event:

  1. The active unit always uses the primary unit's IP addresses and MAC addresses.

  2. When the active unit fails over, the standby unit assumes the IP addresses and MAC addresses of the failed unit and begins passing traffic.

  3. When the failed unit comes back online, it is now in a standby state and takes over the standby IP addresses and MAC addresses.

However, if the secondary unit boots without detecting the primary unit, then the secondary unit becomes the active unit and uses its own MAC addresses, because it does not know the primary unit MAC addresses. When the primary unit becomes available, the secondary (active) unit changes the MAC addresses to those of the primary unit, which can cause an interruption in your network traffic. Similarly, if you swap out the primary unit with new hardware, a new MAC address is used.

Virtual MAC addresses guard against this disruption, because the active MAC addresses are known to the secondary unit at startup, and remain the same in the case of new primary unit hardware. We recommend that you configure the virtual MAC address on both the primary and secondary units to ensure that the secondary unit uses the correct MAC addresses when it is the active unit, even if it comes online before the primary unit. If you do not configure virtual MAC addresses, you might need to clear the ARP tables on connected routers to restore traffic flow. The ASA does not send gratuitous ARPs for static NAT addresses when the MAC address changes, so connected routers do not learn of the MAC address change for these addresses.

Active/Active IP Addresses and MAC Addresses

For Active/Active failover, see the following for IP address and MAC address usage during a failover event:

  1. The primary unit autogenerates active and standby MAC addresses for all interfaces in failover group 1 and 2 contexts. You can also manually configure the MAC addresses if necessary, for example, if there are MAC address conflicts.

  2. Each unit uses the active IP addresses and MAC addresses for its active failover group, and the standby addresses for its standby failover group. For example, the primary unit is active for failover group 1, so it uses the active addresses for contexts in failover group 1. It is standby for the contexts in failover group 2, where it uses the standby addresses.

  3. When a unit fails over, the other unit assumes the active IP addresses and MAC addresses of the failed failover group and begins passing traffic.

  4. When the failed unit comes back online, and you enabled the preempt option, it resumes the failover group.

Virtual MAC Addresses

The ASA has multiple methods to configure virtual MAC addresses. We recommend using only one method. If you set the MAC address using multiple methods, the MAC address used depends on many variables, and might not be predictable. Manual methods include the interface mode mac-address command, the failover mac address command, and for Active/Active failover, the failover group mode mac address command, in addition to autogeneration methods described below.

In multiple context mode, you can configure the ASA to generate virtual active and standby MAC addresses automatically for shared interfaces, and these assignments are synced to the secondary unit (see the mac-address auto command). For non-shared interfaces, you can manually set the MAC addresses for Active/Standby mode (Active/Active mode autogenerates MAC addresses for all interfaces).

For Active/Active failover, virtual MAC addresses are always used, either with default values or with values you can set per interface.

Stateless and Stateful Failover

The ASA supports two types of failover, stateless and stateful for both the Active/Standby and Active/Active modes.


Note

Some configuration elements for clientless SSL VPN (such as bookmarks and customization) use the VPN failover subsystem, which is part of Stateful Failover. You must use Stateful Failover to synchronize these elements between the members of the failover pair. Stateless failover is not recommended for clientless SSL VPN.

Stateless Failover

When a failover occurs, all active connections are dropped. Clients need to reestablish connections when the new active unit takes over.


Note

Some configuration elements for clientless SSL VPN (such as bookmarks and customization) use the VPN failover subsystem, which is part of Stateful Failover. You must use Stateful Failover to synchronize these elements between the members of the failover pair. Stateless (regular) failover is not recommended for clientless SSL VPN.

Stateful Failover

When Stateful Failover is enabled, the active unit continually passes per-connection state information to the standby unit, or in Active/Active failover, between the active and standby failover groups. After a failover occurs, the same connection information is available at the new active unit. Supported end-user applications are not required to reconnect to keep the same communication session.

Supported Features

For Stateful Failover, the following state information is passed to the standby ASA:

  • NAT translation table.

  • TCP and UDP connections and states. Other types of IP protocols, and ICMP, are not parsed by the active unit, because they get established on the new active unit when a new packet arrives.

  • The HTTP connection table (unless you enable HTTP replication).

  • The HTTP connection states (if HTTP replication is enabled)—By default, the ASA does not replicate HTTP session information when Stateful Failover is enabled. We suggest that you enable HTTP replication.

  • SCTP connection states. However, SCTP inspection stateful failover is best effort. During failover, if any SACK packets are lost, the new active unit will drop all other out of order packets in the queue until the missing packet is received.

  • The ARP table

  • The Layer 2 bridge table (for bridge groups)

  • The ISAKMP and IPsec SA table

  • GTP PDP connection database

  • SIP signaling sessions and pin holes.

  • ICMP connection state—ICMP connection replication is enabled only if the respective interface is assigned to an asymmetric routing group.

  • Static and dynamic routing tables—Stateful Failover participates in dynamic routing protocols, like OSPF and EIGRP, so routes that are learned through dynamic routing protocols on the active unit are maintained in a Routing Information Base (RIB) table on the standby unit. Upon a failover event, packets travel normally with minimal disruption to traffic because the active secondary unit initially has rules that mirror the primary unit. Immediately after failover, the re-convergence timer starts on the newly active unit. Then the epoch number for the RIB table increments. During re-convergence, OSPF and EIGRP routes become updated with a new epoch number. Once the timer is expired, stale route entries (determined by the epoch number) are removed from the table. The RIB then contains the newest routing protocol forwarding information on the newly active unit.


    Note

    Routes are synchronized only for link-up or link-down events on an active unit. If the link goes up or down on the standby unit, dynamic routes sent from the active unit may be lost. This is normal, expected behavior.

  • DHCP Server—DHCP address leases are not replicated. However, a DHCP server configured on an interface will send a ping to make sure an address is not being used before granting the address to a DHCP client, so there is no impact to the service. State information is not relevant for DHCP relay or DDNS.

  • Cisco IP SoftPhone sessions—If a failover occurs during an active Cisco IP SoftPhone session, the call remains active because the call session state information is replicated to the standby unit. When the call is terminated, the IP SoftPhone client loses connection with the Cisco Call Manager. This connection loss occurs because there is no session information for the CTIQBE hangup message on the standby unit. When the IP SoftPhone client does not receive a response back from the Call Manager within a certain time period, it considers the Call Manager unreachable and unregisters itself.

  • RA VPN—Remote access VPN end users do not have to reauthenticate or reconnect the VPN session after a failover. However, applications operating over the VPN connection could lose packets during the failover process and not recover from the packet loss.

  • From all the connections, only established ones will be replicated on the Standby ASA.

Unsupported Features

For Stateful Failover, the following state information is not passed to the standby ASA:

  • The user authentication (uauth) table

  • TCP state bypass connections

  • Multicast routing.

  • Selected clientless SSL VPN features:

    • Smart Tunnels

    • Port Forwarding

    • Plugins

    • Java Applets

    • IPv6 clientless or Secure Client sessions

    • Citrix authentication (Citrix users must reauthenticate after failover)

Bridge Group Requirements for Failover

There are special considerations for failover when using bridge groups.

Bridge Group Requirements for Appliances, ASAv

When the active unit fails over to the standby unit, the connected switch port running Spanning Tree Protocol (STP) can go into a blocking state for 30 to 50 seconds when it senses the topology change. To avoid traffic loss while the port is in a blocking state, you can configure one of the following workarounds depending on the switch port mode:

  • Access mode—Enable the STP PortFast feature on the switch: 

    
interface interface_id
  spanning-tree portfast

    The PortFast feature immediately transitions the port into STP forwarding mode upon linkup. The port still participates in STP. So if the port is to be a part of the loop, the port eventually transitions into STP blocking mode.

  • Trunk mode—Block BPDUs on the ASA on a bridge group's member interfaces with an EtherType access rule. 

    
access-list id ethertype deny bpdu
access-group id in interface name1
access-group id in interface name2

    Blocking BPDUs disables STP on the switch. Be sure not to have any loops involving the ASA in your network layout.

If neither of the above options are possible, then you can use one of the following less desirable workarounds that impacts failover functionality or STP stability:

  • Disable interface monitoring.

  • Increase interface holdtime to a high value that will allow STP to converge before the ASAs fail over.

  • Decrease STP timers to allow STP to converge faster than the interface holdtime.

Failover Health Monitoring

The ASA monitors each unit for overall health and for interface health. This section includes information about how the ASA performs tests to determine the state of each unit.

Unit Health Monitoring

The ASA determines the health of the other unit by monitoring the failover link with hello messages. When a unit does not receive three consecutive hello messages on the failover link, the unit sends LANTEST messages on each data interface, including the failover link, to validate whether or not the peer is responsive. For the Firepower 9300 and 4100 series, you can enable Bidirectional Forwarding Detection (BFD) monitoring, which is more reliable than hello messages. The action that the ASA takes depends on the response from the other unit. See the following possible actions:

  • If the ASA receives a response on the failover link, then it does not fail over.

  • If the ASA does not receive a response on the failover link, but it does receive a response on a data interface, then the unit does not failover. The failover link is marked as failed. You should restore the failover link as soon as possible because the unit cannot fail over to the standby while the failover link is down.

  • If the ASA does not receive a response on any interface, then the standby unit switches to active mode and classifies the other unit as failed.

Interface Monitoring

You can monitor up to 1025 interfaces (in multiple context mode, divided between all contexts). You should monitor important interfaces. For example in multiple context mode, you might configure one context to monitor a shared interface: because the interface is shared, all contexts benefit from the monitoring.

When a unit does not receive hello messages on a monitored interface for 15 seconds (the default), it runs interface tests. (To change the period, see the failover polltime interface command, or for Active/Active failover, the polltime interface command) If one of the interface tests fails for an interface, but this same interface on the other unit continues to successfully pass traffic, then the interface is considered to be failed, and the ASA stops running tests.

If the threshold you define for the number of failed interfaces is met (see the failover interface-policy command, or for Active/Active failover, the interface-policy command), and the active unit has more failed interfaces than the standby unit, then a failover occurs. If an interface fails on both units, then both interfaces go into the “Unknown” state and do not count towards the failover limit defined by failover interface policy.

An interface becomes operational again if it receives any traffic. A failed ASA returns to standby mode if the interface failure threshold is no longer met.

If an interface has IPv4 and IPv6 addresses configured on it, the ASA uses the IPv4 addresses to perform the health monitoring. If an interface has only IPv6 addresses configured on it, then the ASA uses IPv6 neighbor discovery instead of ARP to perform the health monitoring tests. For the broadcast ping test, the ASA uses the IPv6 all nodes address (FE02::1).


Note

If a failed unit does not recover and you believe it should not be failed, you can reset the state by entering the failover reset command. If the failover condition persists, however, the unit will fail again.

Interface Tests

The ASA uses the following interface tests. The duration of each test is approximately 1.5 seconds by default, or 1/16 of the failover interface holdtime(see the failover polltime interface command, or for Active/Active failover, the interface-policy command).

  1. Link Up/Down test—A test of the interface status. If the Link Up/Down test indicates that the interface is down, then the ASA considers it failed, and testing stops. If the status is Up, then the ASA performs the Network Activity test.

  2. Network Activity test—A received network activity test. At the start of the test, each unit clears its received packet count for its interfaces. As soon as a unit receives any eligible packets during the test, then the interface is considered operational. If both units receive traffic, then testing stops. If one unit receives traffic and the other unit does not, then the interface on the unit that does not receive traffic is considered failed, and testing stops. If neither unit receives traffic, then the ASA starts the ARP test.

  3. ARP test—A test for successful ARP replies. Each unit sends a single ARP request for the IP address in the most recent entry in its ARP table. If the unit receives an ARP reply or other network traffic during the test, then the interface is considered operational. If the unit does not receive an ARP reply, then the ASA sends a single ARP request for the IP address in the next entry in the ARP table. If the unit receives an ARP reply or other network traffic during the test, then the interface is considered operational. If both units receive traffic, then testing stops. If one unit receives traffic, and the other unit does not, then the interface on the unit that does not receive traffic is considered failed, and testing stops. If neither unit receives traffic, then the ASA starts the Broadcast Ping test.

  4. Broadcast Ping test—A test for successful ping replies. Each unit sends a broadcast ping, and then counts all received packets. If the unit receives any packets during the test, then the interface is considered operational. If both units receive traffic, then testing stops. If one unit receives traffic, and the other unit does not, then the interface on the unit that does not receive traffic is considered failed, and testing stops. If neither unit receives traffic, then testing starts over again with the ARP test. If both units continue to receive no traffic from the ARP and Broadcast Ping tests, then these tests will continue running in perpetuity.

Interface Status

Monitored interfaces can have the following status:

  • Unknown—Initial status. This status can also mean the status cannot be determined.

  • Normal—The interface is receiving traffic.

  • Testing—Hello messages are not heard on the interface for five poll times.

  • Link Down—The interface or VLAN is administratively down.

  • No Link—The physical link for the interface is down.

  • Failed—No traffic is received on the interface, yet traffic is heard on the peer interface.

Failover Times

The following events trigger failover in a Firepower high availability pair:

  • More than 50% of the Snort instances on the active unit are down.

  • Disk space on the active unit is more than 90% full.

  • The no failover active command is run on the active unit or the failover active command is run on the standby unit.

  • The active unit has more failed interfaces than the standby unit.

  • Interface failure on the active device exceeds the threshold configured.

    By default, failure of a single interface causes failover. You can change the default value by configuring a threshold for the number of interfaces or a percentage of monitored interfaces that must fail for the failover to occur. If the threshold breaches on the active device, failover occurs. If the threshold breaches on the standby device, the unit moves to Fail state.

    To change the default failover criteria, enter the following command in global configuration mode:

    Table 1.

    Command

    Purpose

    failover interface-policy num [%]

    hostname (config)# failover interface-policy 20%

    Changes the default failover criteria.

    When specifying a specific number of interfaces, the num argument can be from 1 to 250.

    When specifying a percentage of interfaces, the num argument can be from 1 to 100.


Note

If you manually fail over using the CLI or ASDM, or you reload the ASA, the failover starts immediately and is not subject to the timers listed below.

Table 2. ASA

Failover Condition

Minimum

Default

Maximum

Active unit loses power, hardware goes down, or the software reloads or crashes. When any of these occur, the monitored interfaces or failover link do not receives any hello message.

800 milliseconds

15 seconds

45 seconds

Active unit main board interface link down.

500 milliseconds

5 seconds

15 seconds

Active unit 4GE module interface link down.

2 seconds

5 seconds

15 seconds

Active unit interface up, but connection problem causes interface testing.

5 seconds

25 seconds

75 seconds

Configuration Synchronization

Failover includes various types of configuration synchronization.

Running Configuration Replication

Running configuration replication occurs when any one or both of the devices in the failover pair boot.

In Active/Standby failover, configurations are always synchronized from the active unit to the standby unit.

In Active/Active failover, whichever unit boots second obtains the running configuration from the unit that boots first, regardless of the primary or secondary designation of the booting unit. After both units are up, commands entered in the system execution space are replicated from the unit on which failover group 1 is in the active state.

When the standby/second unit completes its initial startup, it clears its running configuration (except for the failover commands needed to communicate with the active unit), and the active unit sends its entire configuration to the standby/second unit. When the replication starts, the ASA console on the active unit displays the message “Beginning configuration replication: Sending to mate,” and when it is complete, the ASA displays the message “End Configuration Replication to mate.” Depending on the size of the configuration, replication can take from a few seconds to several minutes.

On the unit receiving the configuration, the configuration exists only in running memory. You should save the configuration to flash memory according to Save Configuration Changes. For example, in Active/Active failover, enter the write memory all command in the system execution space on the unit that has failover group 1 in the active state. The command is replicated to the peer unit, which proceeds to write its configuration to flash memory.


Note

During replication, commands entered on the unit sending the configuration may not replicate properly to the peer unit, and commands entered on the unit receiving the configuration may be overwritten by the configuration being received. Avoid entering commands on either unit in the failover pair during the configuration replication process.

File Replication

Configuration syncing does not replicate the following files and configuration components, so you must copy these files manually so they match:

  • Secure Client images

  • CSD images

  • Secure Client profiles

    The ASA uses a cached file for the Secure Client profile stored in cache:/stc/profiles, and not the file stored in the flash file system. To replicate the Secure Client profile to the standby unit, perform one of the following:

    • Enter the write standby command on the active unit.

    • Reapply the profile on the active unit.

    • Reload the standby unit.

  • Local Certificate Authorities (CAs)

  • ASA images

  • ASDM images

Command Replication

After startup, commands that you enter on the active unit are immediately replicated on the standby unit. You do not have to save the active configuration to flash memory to replicate the commands.

In Active/Active failover, commands entered in the system execution space are replicated from the unit on which failover group 1 is in the active state.

Failure to enter the commands on the appropriate unit for command replication to occur causes the configurations to be out of synchronization. Those changes may be lost the next time the initial configuration synchronization occurs.

The following commands are replicated to the standby ASA:

  • All configuration commands except for mode, firewall , and failover lan unit

  • copy running-config startup-config

  • delete

  • mkdir

  • rename

  • rmdir

  • write memory

The following commands are not replicated to the standby ASA:

  • All forms of the copy command except for copy running-config startup-config

  • All forms of the write command except for write memory

  • debug

  • failover lan unit

  • firewall

  • show

  • terminal pager and pager

Config-Sync Optimization

When there is node reboot or node rejoin following suspend or resume failover, the joining unit clears its running configuration. The active unit sends its entire configuration to the joining unit for a full config-sync. If the active unit has large configuration, the joining unit takes several minutes to synchronize the configuration.

The Config-Sync Optimization feature enables comparing the configuration of the joining unit and the active unit by exchanging config-hash values. If the hash computed on both active and joining units match, the joining unit skips full configuration synchronization and rejoin the HA. This feature enables faster HA peering and reduces maintenance window and upgrade time.

Guidelines and Limitations of Config-Sync Optimization

  • The Config-Sync Optimization feature is enabled by default on ASA version 9.18.1 and later.

  • ASA multiple context mode supports the Config-Sync Optimization feature by sharing the context order during full configuration synchronization, allowing comparison of context order during subsequent node-rejoin.

  • If you configure passphrase and failover IPsec key, then Config-Sync Optimization is not effective as the hash value computed in the active and standby unit differs.

  • If you configure the device with dynamic ACL or SNMPv3, the Config-Sync Optimization feature is not effective.

  • Active unit syncs full configuration with flapping LAN links as default behavior. During failover flaps between active and standby units, the Config-Sync Optimization feature is not triggered and performs a full configuration synchronization.

Monitoring Config-Sync Optimization

When Config-Sync Optimization feature is enabled, syslog messages are generated displaying whether the hash values computed on the active and joining unit match, does not match, or if the operation timeout expires. The syslog message also displays the time elapsed, from the time of sending the hash request to the time of getting and comparing the hash response.

Use the following commands for monitoring Config-Sync Optimization.

  • show failover config-sync checksum

    Displays information about the device status and checksum.

  • show failover config-sync configuration

    Displays information about the device configuration and checksum.

  • show failover config-sync status

    Displays status of Config Sync Optimization feature.

About Active/Standby Failover

Active/Standby failover lets you use a standby ASA to take over the functionality of a failed unit. When the active unit fails, the standby unit becomes the active unit. However, you must set the standby unit to primary before the failed unit is replaced, in order to retain the configuration of the secondary unit.


Note

For multiple context mode, the ASA can fail over the entire unit (including all contexts) but cannot fail over individual contexts separately.

Primary/Secondary Roles and Active/Standby Status

The main differences between the two units in a failover pair are related to which unit is active and which unit is standby, namely which IP addresses to use and which unit actively passes traffic.

However, a few differences exist between the units based on which unit is primary (as specified in the configuration) and which unit is secondary:

  • The primary unit always becomes the active unit if both units start up at the same time (and are of equal operational health).

  • The primary unit MAC addresses are always coupled with the active IP addresses. The exception to this rule occurs when the secondary unit becomes active and cannot obtain the primary unit MAC addresses over the failover link. In this case, the secondary unit MAC addresses are used.

Active Unit Determination at Startup

The active unit is determined by the following:

  • If a unit boots and detects a peer already running as active, it becomes the standby unit.

  • If a unit boots and does not detect a peer, it becomes the active unit.

  • If both units boot simultaneously, then the primary unit becomes the active unit, and the secondary unit becomes the standby unit.

Failover Events

In Active/Standby failover, failover occurs on a unit basis. Even on systems running in multiple context mode, you cannot fail over individual or groups of contexts.

The following table shows the failover action for each failure event. For each failure event, the table shows the failover policy (failover or no failover), the action taken by the active unit, the action taken by the standby unit, and any special notes about the failover condition and actions.

Table 3. Failover Events

Failure Event

Policy

Active Unit Action

Standby Unit Action

Notes

Active unit failed (power or hardware)

Failover

n/a

Become active

Mark active as failed

No hello messages are received on any monitored interface or the failover link.

Formerly active unit recovers

No failover

Become standby

No action

None.

Standby unit failed (power or hardware)

No failover

Mark standby as failed

n/a

When the standby unit is marked as failed, then the active unit does not attempt to fail over, even if the interface failure threshold is surpassed.

Failover link failed during operation

No failover

Mark failover link as failed

Mark failover link as failed

You should restore the failover link as soon as possible because the unit cannot fail over to the standby unit while the failover link is down.

Failover link failed at startup

No failover

Become active

Mark failover link as failed

Become active

Mark failover link as failed

If the failover link is down at startup, both units become active.

State link failed

No failover

No action

No action

State information becomes out of date, and sessions are terminated if a failover occurs.

Interface failure on active unit above threshold

Failover

Mark active as failed

Become active

None.

Interface failure on standby unit above threshold

No failover

No action

Mark standby as failed

When the standby unit is marked as failed, then the active unit does not attempt to fail over even if the interface failure threshold is surpassed.

About Active/Active Failover

This section describes Active/Active failover.

Active/Active Failover Overview

In an Active/Active failover configuration, both ASAs can pass network traffic. Active/Active failover is only available to ASAs in multiple context mode. In Active/Active failover, you divide the security contexts on the ASA into a maximum of 2 failover groups.

A failover group is simply a logical group of one or more security contexts. You can assign failover group to be active on the primary ASA, and failover group 2 to be active on the secondary ASA. When a failover occurs, it occurs at the failover group level. For example, depending on interface failure patterns, it is possible for failover group 1 to fail over to the secondary ASA, and subsequently failover group 2 to fail over to the primary ASA. This event could occur if the interfaces in failover group 1 are down on the primary ASA but up on the secondary ASA, while the interfaces in failover group 2 are down on the secondary ASA but up on the primary ASA.

The admin context is always a member of failover group 1. Any unassigned security contexts are also members of failover group 1 by default. If you want Active/Active failover, but are otherwise uninterested in multiple contexts, the simplest configuration would be to add one additional context and assign it to failover group 2.


Note

When configuring Active/Active failover, make sure that the combined traffic for both units is within the capacity of each unit.


Note

You can assign both failover groups to one ASA if desired, but then you are not taking advantage of having two active ASAs.

Primary/Secondary Roles and Active/Standby Status for a Failover Group

As in Active/Standby failover, one unit in an Active/Active failover pair is designated the primary unit, and the other unit the secondary unit. Unlike Active/Standby failover, this designation does not indicate which unit becomes active when both units start simultaneously. Instead, the primary/secondary designation does two things:

  • The primary unit provides the running configuration to the pair when they boot simultaneously.

  • Each failover group in the configuration is configured with a primary or secondary unit preference. When used with preemption, this preference ensures that the failover group runs on the correct unit after it starts up. Without preemption, both groups run on the first unit to boot up.

Active Unit Determination for Failover Groups at Startup

The unit on which a failover group becomes active is determined as follows:

  • When a unit boots while the peer unit is not available, both failover groups become active on the unit.

  • When a unit boots while the peer unit is active (with both failover groups in the active state), the failover groups remain in the active state on the active unit regardless of the primary or secondary preference of the failover group until one of the following occurs:

    • A failover occurs.

    • A failover is manually forced.

    • A preemption for the failover group is configured, which causes the failover group to automatically become active on the preferred unit when the unit becomes available.

Failover Events

In an Active/Active failover configuration, failover occurs on a failover group basis, not a system basis. For example, if you designate both failover groups as Active on the primary unit, and failover group 1 fails, then failover group 2 remains Active on the primary unit while failover group 1 becomes active on the secondary unit.

Because a failover group can contain multiple contexts, and each context can contain multiple interfaces, it is possible for all interfaces in a single context to fail without causing the associated failover group to fail.

The following table shows the failover action for each failure event. For each failure event, the policy (whether or not failover occurs), actions for the active failover group, and actions for the standby failover group are given.

Table 4. Failover Events

Failure Event

Policy

Active Group Action

Standby Group Action

Notes

A unit experiences a power or software failure

Failover

Become standby

Mark as failed

Become active

Mark active as failed

When a unit in a failover pair fails, any active failover groups on that unit are marked as failed and become active on the peer unit.

Interface failure on active failover group above threshold

Failover

Mark active group as failed

Become active

None.

Interface failure on standby failover group above threshold

No failover

No action

Mark standby group as failed

When the standby failover group is marked as failed, the active failover group does not attempt to fail over, even if the interface failure threshold is surpassed.

Formerly active failover group recovers

No failover

No action

No action

Unless failover group preemption is configured, the failover groups remain active on their current unit.

Failover link failed at startup

No failover

Become active

Become active

If the failover link is down at startup, both failover groups on both units become active.

State link failed

No failover

No action

No action

State information becomes out of date, and sessions are terminated if a failover occurs.

Failover link failed during operation

No failover

n/a

n/a

Each unit marks the failover link as failed. You should restore the failover link as soon as possible because the unit cannot fail over to the standby unit while the failover link is down.

Licensing for Failover

For most models, failover units do not require the same license on each unit. If you have licenses on both units, they combine into a single running failover cluster license. There are some exceptions to this rule. See the following table for precise licensing requirements for failover.

Model

License Requirement

ASA Virtual

See Failover Licenses for the ASAv.

Firepower 1010

Security Plus license on both units. See Failover Licenses for the Firepower 1010.

Firepower 1100

See Failover Licenses for the Firepower 1100.

Firepower 2100

See Failover Licenses for the Firepower 2100.

Secure Firewall 3100

See Failover Licenses for the Secure Firewall 3100.

Firepower 4100/9300

See Failover Licenses for the Firepower 4100/9300.

ISA 3000

Security Plus license on both units.

Note

 

Each unit must have the same encryption license.


Note

A valid permanent key is required; in rare instances on the ISA 3000, your PAK authentication key can be removed. If your key consists of all 0’s, then you need to reinstall a valid authentication key before failover can be enabled.

Guidelines for Failover

Context Mode

  • Active/Active mode is supported only in multiple context mode.

  • For multiple context mode, perform all steps in the system execution space unless otherwise noted.

Model Support

  • Firepower 1010:

    • You should not use the switch port functionality when using Failover. Because the switch ports operate in hardware, they continue to pass traffic on both the active and the standby units. Failover is designed to prevent traffic from passing through the standby unit, but this feature does not extend to switch ports. In a normal Failover network setup, active switch ports on both units will lead to network loops. We suggest that you use external switches for any switching capability. Note that VLAN interfaces can be monitored by failover, while switch ports cannot. Theoretically, you can put a single switch port on a VLAN and successfully use Failover, but a simpler setup is to use physical firewall interfaces instead.

    • You can only use a firewall interface as the failover link.

  • Firepower 9300—We recommend that you use inter-chassis Failover for the best redundancy.

  • The ASA virtual on public cloud networks such as Microsoft Azure and Amazon Web Services are not supported with regular Failover because Layer 2 connectivity is required. Instead, see Failover for High Availability in the Public Cloud.

ASA Virtual Failover for High Availability

When creating a failover pair with the ASA virtual, it is necessary to add the data interfaces to each ASA virtual in the same order. If the exact same interfaces are added to each ASA virtual, but in different order, errors may be presented at the ASA virtual Console. Failover functionality may also be affected

Additional Guidelines

  • When the active unit fails over to the standby unit, the connected switch port running Spanning Tree Protocol (STP) can go into a blocking state for 30 to 50 seconds when it senses the topology change. To avoid traffic loss while the port is in a blocking state, you can enable the STP PortFast feature on the switch:

    interface interface_id spanning-tree portfast

    This workaround applies to switches connected to both routed mode and bridge group interfaces. The PortFast feature immediately transitions the port into STP forwarding mode upon linkup. The port still participates in STP. So if the port is to be a part of the loop, the port eventually transitions into STP blocking mode.

  • Configuring port security on the switches connected to the ASA failover pair can cause communication problems when a failover event occurs. This problem occurs when a secure MAC address configured or learned on one secure port moves to another secure port, a violation is flagged by the switch port security feature.

  • You can monitor up to 1025 interfaces on a unit, across all contexts.

  • For Active/Standby Failover and a VPN IPsec tunnel, you cannot monitor both the active and standby units using SNMP over the VPN tunnel. The standby unit does not have an active VPN tunnel, and will drop traffic destined for the NMS. You can instead use SNMPv3 with encryption so the IPsec tunnel is not required.

  • For Active/Active failover, no two interfaces in the same context should be configured in the same ASR group.

  • For Active/Active failover, you can define a maximum of two failover groups.

  • For Active/Active failover, when removing failover groups, you must remove failover group 1 last. Failover group1 always contains the admin context. Any context not assigned to a failover group defaults to failover group 1. You cannot remove a failover group that has contexts explicitly assigned to it.

  • Immediately after failover, the source address of syslog messages will be the failover interface address for a few seconds.

  • For better convergence (during a failover), you must shut down the interfaces on a HA pair that are not associated with any configuration or instance.

  • If you configure HA failover encryption in evaluation mode, the systems use DES for the encryption. If you then register the devices using an export-compliant account, the devices will use AES after a reboot. Thus, if a system reboots for any reason, including after installing an upgrade, the peers will be unable to communicate and both units will become the active unit. We recommend that you do not configure encryption until after you register the devices. If you do configure this in evaluation mode, we recommend you remove the encryption before registering the devices.

  • When using SNMPv3 with failover, if you replace a failover unit, then SNMPv3 users are not replicated to the new unit. You must re-add the SNMPv3 users to the active unit to force the users to replicate to the new unit; or you can add the users directly on the new unit. Reconfigure each user by entering the snmp-server user username group-name v3 command on the active unit or directly to the standby unit with the priv-password option and auth-password option in their unencrypted forms.

  • The ASA does not share SNMP client engine data with its peer.

  • If you have a very large number of access control and NAT rules, the size of the configuration can prevent efficient configuration replication, resulting in the standby unit taking an excessively long time to reach standby ready state. This can also impact your ability to connect to the standby unit during replication through the console or SSH session. To enhance configuration replication performance, enable transactional commit for both access rules and NAT, using the asp rule-engine transactional-commit access-group and asp rule-engine transactional-commit nat commands.

  • A unit in a high availability pair transitioning to the standby role synchronizes its clock with the active unit.

    Example:

    firepower#show clock
01:00:52 UTC Mar 1 2022

...
01:01:18 UTC Mar 1 2022 <======= Incorrect (previous) clock
Cold Standby               Sync Config                Detected an Active mate

19:38:21 UTC Apr 9 2022 <======= Updated clock
Sync Config                Sync File System           Detected an Active mate
...
firepower/sec/stby#show clock
19:38:40 UTC Apr 9 2022

  • The units in high availability (failover) do not dynamically synchronize the clock. Here are some examples of events when synchronization takes place:

    • A new HA pair is created.

    • HA is broken and re-created.

    • Communication over the failover link was disrupted and reestablished.

    • Failover status was manually changed using the no failover/failover or configure high-availability suspend/resume (threat defense CLISH) commands.

  • In ASA/threat defense HA pairs running on platforms, the synchronization is applicable only to the applications, such as ASA/threat defense, not the chassis.

  • Enabling HA forces all routes to be deleted and are re-added after the HA progression changes to Active state. You could experience connection loss during this phase.

  • During threat defense high availability creation using the management center or the device manager, all the existing configurations on the selected secondary threat defense unit are replaced with the configuration replicated from the selected primary threat defense unit, so select your primary unit carefully during high availability (HA) creation. For example, if HA is broken and re-created when the existing primary unit becomes faulty and is replaced using Return Material Authorization (RMA), then during HA creation, the replacement unit should be selected as the secondary unit so that all the configurations from the selected primary unit are replicated to the replacement unit.

  • Deploying Cisco Firepower 2100 and 1100 threat defense devices in HA with hundreds of interfaces configured on them can result in increased delay in the failover time (seconds).

  • If you enable failover on a standalone device, the data interfaces go down at negotiation state of HA, interrupting traffic.

  • In an ASA or threat defense HA configuration, short-lived connections, usually using port 53, are closed quickly and never transferred or synchronized from Active to Standby, so there might be a difference in the number of connections on both HA devices. This is expected behavior for short-lived connections. You can try to compare the connections that are long-lived ( for example, more than 30-60 seconds).

Defaults for Failover

By default, the failover policy consists of the following:

  • No HTTP replication in Stateful Failover.

  • A single interface failure causes failover.

  • The interface poll time is 5 seconds.

  • The interface hold time is 25 seconds.

  • The unit poll time is 1 second.

  • The unit hold time is 15 seconds.

  • Virtual MAC addresses are disabled in multiple context mode.

  • Monitoring on all physical interfaces.

Configure Active/Standby Failover

To configure Active/Standby failover, configure basic failover settings on both the primary and secondary units. All other configuration occurs only on the primary unit, and is then synched to the secondary unit.

Configure the Primary Unit for Active/Standby Failover

Follow the steps in this section to configure the primary in an Active/Standby failover configuration. These steps provide the minimum configuration needed to enable failover on the primary unit.

Before you begin

  • We recommend that you configure standby IP addresses for all interfaces except for the failover and state links. If you use a 31-bit subnet mask for point-to-point connections, do not configure a standby IP address. You will not be able to enable failover if any interfaces are configured for DHCP.

  • Do not configure a nameif for the failover and state links.

  • For multiple context mode, complete this procedure in the system execution space. To change from the context to the system execution space, enter the changeto system command.

Procedure

Step 1

Designate this unit as the primary unit:

failover lan unit primary

Step 2

Specify the interface to be used as the failover link:

failover lan interface if_name interface_id

Example:


ciscoasa(config)# failover lan interface folink gigabitethernet0/3

This interface cannot be used for any other purpose (except, optionally, the state link).

The if_name argument assigns a name to the interface.

The interface_id argument can be a data physical interface, subinterface, or EtherChannel interface ID. On the Firepower 1010, the interface is a firewall interface ID; you cannot specify a switch port ID or VLAN ID. For the Firepower 4100/9300, you can use any data-type interface.

Step 3

Assign the active and standby IP addresses to the failover link:

failover interface ip failover_if_name {ip_address mask | ipv6_address / prefix} standby ip_address

Example:


ciscoasa(config)# failover interface ip folink 172.27.48.1 255.255.255.0 standby 172.27.48.2

Or: 


ciscoasa(config)# failover interface ip folink 2001:a0a:b00::a0a:b70/64 standby 2001:a0a:b00::a0a:b71

This address should be on an unused subnet. This subnet can be 31-bits (255.255.255.254) with only two IP addresses. 169.254.0.0/16 and fd00:0:0:*::/64 are internally used subnets, and you cannot use them for the failover or state links.

The standby IP address must be in the same subnet as the active IP address.

Step 4

Enable the failover link:

interface failover_interface_id   

no shutdown

Example:


ciscoasa(config)# interface gigabitethernet 0/3
ciscoasa(config-if)# no shutdown

Step 5

(Optional) If you want to use a separate interface for the state link, specify the interface.

failover link if_name interface_id

Example:


ciscoasa(config)# failover link folink gigabitethernet0/4

If you do not specify a separate interface, then the failover link is used for the statelink.

The if_name argument assigns a name to the interface.

The interface_id argument can be a physical interface, subinterface, or EtherChannel interface ID. On the Firepower 1010, the interface is a firewall interface ID; you cannot specify a switch port ID or VLAN ID.

Step 6

If you specified a separate state link, assign the active and standby IP addresses to the state link:

failover interface ip state_if_name {ip_address mask | ipv6_address/prefix} standby ip_address

Example:


ciscoasa(config)# failover interface ip statelink 172.27.49.1 255.255.255.0 standby 172.27.49.2

Or: 


ciscoasa(config)# failover interface ip statelink 2001:a0a:b00:a::a0a:b70/64 standby 2001:a0a:b00:a::a0a:b71

This address should be on an unused subnet, different from the failover link. This subnet can be 31-bits (255.255.255.254) with only two IP addresses. 169.254.0.0/16 and fd00:0:0:*::/64 are internally used subnets, and you cannot use them for the failover or state links.

The standby IP address must be in the same subnet as the active IP address.

Skip this step if you are sharing the state link.

Step 7

If you specified a separate state link, enable the state link.

interface state_interface_id

no shutdown  

Example:


ciscoasa(config)# interface gigabitethernet 0/4
ciscoasa(config-if)# no shutdown

Skip this step if you are sharing the state link.

Step 8

(Optional) Do one of the following to encrypt communications on the failover and state links:

  • (Preferred) Establish IPsec LAN-to-LAN tunnels on the failover and state links between the units to encrypt all failover communications:

    failover ipsec pre-shared-key [0 | 8] key

    Example: 

    
ciscoasa(config)# failover ipsec pre-shared-key a3rynsun

    The key can be up to 128 characters in length. Identify the same key on both units. The key is used by IKEv2 to establish the tunnels.

    If you use a master passphrase (see Configure the Master Passphrase), then the key is encrypted in the configuration. If you are copying from the configuration (for example, from more system:running-config output), specify that the key is encrypted by using the 8 keyword. 0 is used by default, specifying an unencrypted password.

    The failover ipsec pre-shared-key shows as ***** in show running-config output; this obscured key is not copyable.

    If you do not configure failover and state link encryption, failover communication, including any passwords or keys in the configuration that are sent during command replication, will be in clear text.

    You cannot use both IPsec encryption and the legacy failover key encryption. If you configure both methods, IPsec is used. However, if you use the master passphrase, you must first remove the failover key using the no failover key command before you configure IPsec encryption.

    Failover LAN-to-LAN tunnels do not count against the IPsec (Other VPN) license.

  • (Optional) Encrypt failover communication on the failover and state links:

    failover key [0 | 8] {hex key | shared_secret}

    Example: 

    
ciscoasa(config)# failover key johncr1cht0n

    Use a shared_secret from 1 to 63 characters or a 32-character hex key. For the shared_secret, you can use any combination of numbers, letters, or punctuation. The shared secret or hex key is used to generate the encryption key. Identify the same key on both units.

    If you use a master passphrase (see Configure the Master Passphrase), then the shared secret or hex key is encrypted in the configuration. If you are copying from the configuration (for example, from more system:running-config output), specify that the shared secret or hex key is encrypted by using the 8 keyword. 0 is used by default, specifying an unencrypted password.

    The failover key shared secret shows as ***** in show running-config output; this obscured key is not copyable.

    If you do not configure failover and state link encryption, failover communication, including any passwords or keys in the configuration that are sent during command replication, will be in clear text.

Step 9

Enable failover:

failover

Step 10

Save the system configuration to flash memory:

write memory

Examples

The following example configures the failover parameters for the primary unit: 


failover lan unit primary
failover lan interface folink gigabitethernet0/3

failover interface ip folink 172.27.48.0 255.255.255.254 standby 172.27.48.1
interface gigabitethernet 0/3
  no shutdown
failover link folink gigabitethernet0/3
failover ipsec pre-shared-key a3rynsun
failover

Configure the Secondary Unit for Active/Standby Failover

The only configuration required on the secondary unit is for the failover link. The secondary unit requires these commands to communicate initially with the primary unit. After the primary unit sends its configuration to the secondary unit, the only permanent difference between the two configurations is the failover lan unit command, which identifies each unit as primary or secondary.

Before you begin

  • You will not be able to enable failover if any interfaces are configured for DHCP.

  • Do not configure a nameif for the failover and state links.

  • For multiple context mode, complete this procedure in the system execution space. To change from the context to the system execution space, enter the changeto system command.

Procedure

Step 1

Re-enter the exact same commands as on the primary unit except for the failover lan unit primary command. You can optionally replace it with the failover lan unit secondary command, but it is not necessary because secondary is the default setting. See Configure the Primary Unit for Active/Standby Failover.

For example: 


ciscoasa(config)# failover lan interface folink gigabitethernet0/3
INFO: Non-failover interface config is cleared on GigabitEthernet0/3 and its sub-interfaces
ciscoasa(config)# failover interface ip folink 172.27.48.1 255.255.255.0 standby 172.27.48.2
ciscoasa(config)# interface gigabitethernet 0/3
ciscoasa(config-ifc)# no shutdown
ciscoasa(config)# failover ipsec pre-shared-key a3rynsun
ciscoasa(config)# failover

Step 2

After the failover configuration syncs, save the configuration to flash memory: 


ciscoasa(config)# write memory

Configure Active/Active Failover

This section tells how to configure Active/Active failover.

Configure the Primary Unit for Active/Active Failover

Follow the steps in this section to configure the primary unit in an Active/Active failover configuration. These steps provide the minimum configuration needed to enable failover on the primary unit.

Before you begin

  • Enable multiple context mode according to Enable or Disable Multiple Context Mode.

  • We recommend that you configure standby IP addresses for all interfaces except for the failover and state links according to Routed and Transparent Mode Interfaces. If you use a 31-bit subnet mask for point-to-point connections, do not configure a standby IP address. You will not be able to enable failover if any interfaces are configured for DHCP.

  • Do not configure a nameif for the failover and state links.

  • Complete this procedure in the system execution space. To change from the context to the system execution space, enter the changeto system command.

Procedure

Step 1

Designate this unit as the primary unit:

failover lan unit primary

Step 2

Specify the interface to be used as the failover link:

failover lan interface if_name interface_id

Example:


ciscoasa(config)# failover lan interface folink gigabitethernet0/3

This interface cannot be used for any other purpose (except, optionally, the state link).

The if_name argument assigns a name to the interface.

The interface_id argument can be a physical interface, subinterface, or EtherChannel interface ID. For the Firepower 4100/9300, you can use any data-type interface.

Step 3

Assign the active and standby IP addresses to the failover link:

standby failover interface ip if_name {ip_address mask | ipv6_address/prefix } standby ip_address

Example:


ciscoasa(config)# failover interface ip folink 172.27.48.1 255.255.255.0 standby 172.27.48.2

Or: 


ciscoasa(config)# failover interface ip folink 2001:a0a:b00::a0a:b70/64 standby 2001:a0a:b00::a0a:b71

This address should be on an unused subnet. This subnet can be 31-bits (255.255.255.254) with only two IP addresses. 169.254.0.0/16 and fd00:0:0:*::/64 are internally used subnets, and you cannot use them for the failover or state links.

The standby IP address must be in the same subnet as the active IP address.

Step 4

Enable the failover link:

interface failover_interface_id

no shutdown  

Example:


ciscoasa(config)# interface gigabitethernet 0/3
ciscoasa(config-if)# no shutdown

Step 5

(Optional) If you want to use a separate interface for the state link, specify the interface.

failover link if_name interface_id

Example:


ciscoasa(config)# failover link statelink gigabitethernet0/4

We recommend that you use a separate state link from the failover link. If you do not specify a separate interface, then the failover link is used for the statelink.

The if_name argument assigns a name to the interface.

The interface_id argument can be a physical interface, subinterface, or EtherChannel interface ID.

Step 6

If you specified a separate state link, assign the active and standby IP addresses to the state link:

This address should be on an unused subnet, different from the failover link. This subnet can be 31-bits (255.255.255.254) with only two IP addresses. 169.254.0.0/16 and fd00:0:0:*::/64 are internally used subnets, and you cannot use them for the failover or state links.

The standby IP address must be in the same subnet as the active IP address.

Skip this step if you are sharing the state link.

failover interface ip state if_name {ip_address mask | ipv6_address/prefix} standby ip_address

Example:


ciscoasa(config)# failover interface ip statelink 172.27.49.1 255.255.255.0 standby 172.27.49.2

Or: 


ciscoasa(config)# failover interface ip statelink 2001:a0a:b00:a::a0a:b70/64 standby 2001:a0a:b00:a::a0a:b71

Step 7

If you specified a separate state link, enable the state link:

interface state_interface_id   

no shutdown

Example:


ciscoasa(config)# interface gigabitethernet 0/4
ciscoasa(config-if)# no shutdown

Skip this step if you are sharing the state link.

Step 8

(Optional) Do one of the following to encrypt communications on the failover and state links:

  • (Preferred) Establish IPsec LAN-to-LAN tunnels on the failover and state links between the units to encrypt all failover communications:

    failover ipsec pre-shared-key [0 | 8] key 

    
ciscoasa(config)# failover ipsec pre-shared-key a3rynsun

    The key can be up to 128 characters in length. Identify the same key on both units. The key is used by IKEv2 to establish the tunnels.

    If you use a master passphrase (see Configure the Master Passphrase), then the key is encrypted in the configuration. If you are copying from the configuration (for example, from more system:running-config output), specify that the key is encrypted by using the 8 keyword. 0 is used by default, specifying an unencrypted password.

    The failover ipsec pre-shared-key shows as ***** in show running-config output; this obscured key is not copyable.

    If you do not configure failover and state link encryption, failover communication, including any passwords or keys in the configuration that are sent during command replication, will be in clear text.

    You cannot use both IPsec encryption and the legacy failover key encryption. If you configure both methods, IPsec is used. However, if you use the master passphrase, you must first remove the failover key using the no failover key command before you configure IPsec encryption.

    Failover LAN-to-LAN tunnels do not count against the IPsec (Other VPN) license.

  • (Optional) Encrypt failover communication on the failover and state links:

    failover key [0 | 8] {hex key | shared_secret} 

    
ciscoasa(config)# failover key johncr1cht0n

    Use a shared_secret, from 1 to 63 characters, or a 32-character hex key.

    For the shared_secret, you can use any combination of numbers, letters, or punctuation. The shared secret or hex key is used to generate the encryption key. Identify the same key on both units.

    If you use a master passphrase (see Configure the Master Passphrase), then the shared secret or hex key is encrypted in the configuration. If you are copying from the configuration (for example, from more system:running-config output), specify that the shared secret or hex key is encrypted by using the 8 keyword. 0 is used by default, specifying an unencrypted password.

    The failover key shared secret shows as ***** in show running-config output; this obscured key is not copyable.

    If you do not configure failover and state link encryption, failover communication, including any passwords or keys in the configuration that are sent during command replication, will be in clear text.

Step 9

Create failover group 1:

failover group 1

primary

preempt [delay]

Example:


ciscoasa(config-fover-group)# failover group 1
ciscoasa(config-fover-group)# primary
ciscoasa(config-fover-group)# preempt 1200

Typically, you assign group 1 to the primary unit, and group 2 to the secondary unit. Both failover groups become active on the unit that boots first (even if it seems like they boot simultaneously, one unit becomes active first), despite the primary or secondary setting for the group. The preempt command causes the failover group to become active on the designated unit automatically when that unit becomes available.

You can enter an optional delay value, which specifies the number of seconds the failover group remains active on the current unit before automatically becoming active on the designated unit. Valid values are from 1 to 1200.

If Stateful Failover is enabled, the preemption is delayed until the connections are replicated from the unit on which the failover group is currently active.

If you manually fail over, the preempt command is ignored.

Step 10

Create failover group 2 and assign it to the secondary unit:

failover group 2  

secondary

preempt [delay]

Example:


ciscoasa(config-fover-group)# failover group 2
ciscoasa(config-fover-group)# secondary
ciscoasa(config-fover-group)# preempt 1200

Step 11

Enter the context configuration mode for a given context, and assign the context to a failover group:

context name

join-failover-group {1 | 2}   

Example:


ciscoasa(config)# context Eng
ciscoasa(config-ctx)# join-failover-group 2

Repeat this command for each context.

Any unassigned contexts are automatically assigned to failover group 1. The admin context is always a member of failover group 1; you cannot assign it to group 2.

Step 12

Enable failover:

failover

Step 13

Save the system configuration to flash memory:

write memory

Examples

The following example configures the failover parameters for the primary unit: 


failover lan unit primary
failover lan interface folink gigabitethernet0/3

failover interface ip folink 172.27.48.0 255.255.255.254 standby 172.27.48.1
interface gigabitethernet 0/3
  no shutdown
failover link statelink gigabitethernet0/4

failover interface ip statelink 172.27.48.2 255.255.255.254 standby 172.27.48.3
interface gigabitethernet 0/4
  no shutdown
failover group 1
  primary
  preempt
failover group 2
  secondary
  preempt
context admin
  join-failover-group 1
failover ipsec pre-shared-key a3rynsun
failover

Configure the Secondary Unit for Active/Active Failover

The only configuration required on the secondary unit is for the failover link. The secondary unit requires these commands to communicate initially with the primary unit. After the primary unit sends its configuration to the secondary unit, the only permanent difference between the two configurations is the failover lan unit command, which identifies each unit as primary or secondary.

Before you begin

  • Enable multiple context mode according to Enable or Disable Multiple Context Mode.

  • You will not be able to enable failover if any interfaces are configured for DHCP.

  • Do not configure a nameif for the failover and state links.

  • Complete this procedure in the system execution space. To change from the context to the system execution space, enter the changeto system command.

Procedure

Step 1

Re-enter the exact same commands as on the primary unit except for the failover lan unit primary command. You can optionally replace it with the failover lan unit secondary command, but it is not necessary because secondary is the default setting. You also do not need to enter the failover group and join-failover-group commands, as they are replicated from the primary unit. See Configure the Primary Unit for Active/Active Failover.

For example: 


ciscoasa(config)# failover lan interface folink gigabitethernet0/3
INFO: Non-failover interface config is cleared on GigabitEthernet0/3 and its sub-interfaces
ciscoasa(config)# failover interface ip folink 172.27.48.1 255.255.255.0 standby 172.27.48.2
ciscoasa(config)# interface gigabitethernet 0/3
no shutdown
ciscoasa(config)# failover link statelink gigabitethernet0/4
INFO: Non-failover interface config is cleared on GigabitEthernet0/4 and its sub-interfaces
ciscoasa(config)# failover interface ip statelink 172.27.49.1 255.255.255.0 standby 172.27.49.2
ciscoasa(config)# interface gigabitethernet 0/4
no shutdown
ciscoasa(config)# failover ipsec pre-shared-key a3rynsun
ciscoasa(config)# failover

Step 2

After the failover configuration syncs from the primary unit, save the configuration to flash memory:

ciscoasa(config)# write memory

Step 3

If necessary, force failover group 2 to be active on the secondary unit:

failover active group 2

Configure Optional Failover Parameters

You can customize failover settings as desired.

Configure Failover Criteria and Other Settings

See Defaults for Failover for the default settings for many parameters that you can change in this section. For Active/Active mode, you set most criteria per failover group.

Before you begin

  • Configure these settings in the system execution space in multiple context mode.

  • For Bidirectional Forwarding Detection (BFD) for unit health monitoring, see the following limitations:

    • Firepower 9300 and 4100 only.

    • Active/Standby only.

    • Routed mode only

Procedure

Step 1

Change the unit poll and hold times:

failover polltime [unit] [msec] poll_time [holdtime [msec] time]

Example:


ciscoasa(config)# failover polltime unit msec 200 holdtime msec 800

The polltime range is between 1 and 15 seconds or between 200 and 999 milliseconds. The holdtime range is between 1and 45 seconds or between 800 and 999 milliseconds.You cannot enter a holdtime value that is less than 3 times the unit poll time. With a faster poll time, the ASA can detect failure and trigger failover faster. However, faster detection can cause unnecessary switchovers when the network is temporarily congested.

If a unit does not hear hello packet on the failover communication interface for one polling period, additional testing occurs through the remaining interfaces. If there is still no response from the peer unit during the hold time, the unit is considered failed and, if the failed unit is the active unit, the standby unit takes over as the active unit.

In Active/Active mode, you set this rate for the system; you cannot set this rate per failover group.

Step 2

Configure BFD for unit health monitoring.

The regular unit monitoring can cause false alarms when CPU usage is high. The BFD method is distributed, so high CPU does not affect its operation.

  1. Define a BFD template to be used for failover health detection:

    bfd-template single-hop template_name

    bfd interval min-tx millisecondsmin-rx milliseconds multiplier multiplier_value

    Example:

    
ciscoasa(config)# bfd template single-hop failover-temp 
ciscoasa(config-bfd)# bfd interval min-tx 50 min-rx 50 multiplier 3

    The min-tx specifies the rate at which BFD control packets are sent to the failover peer. The range is 50 to 999 milliseconds. The min-rx specifies the rate at which BFD control packets are expected to be received from the failover peer. The range is 50 to 999 milliseconds. The multiplier specifies the number of consecutive BFD control packets that must be missed from a failover peer before BFD declares that the peer is unavailable. The range is 3 to 50.

    You can also configure echo and authentication for this template; see Create the BFD Template.

  2. Enable BFD for health monitoring:

    failover health-check bfd template_name

    Example:

    
ciscoasa(config)# failover health-check bfd failover-temp

Step 3

Change the interface link state poll time:

failover polltime link-state msec poll_time

Example:


ciscoasa(config)# failover polltime link-state msec 300

The range is between 300 and 799 milliseconds. By default, each ASA in a failover pair checks the link state of its interfaces every 500 msec. You can customize the polltime; for example, if you set the polltime to 300 msec, the ASA can detect an interface failure and trigger failover faster.

In Active/Active mode, you set this rate for the system; you cannot set this rate per failover group.

Step 4

Set the session replication rate in connections per second:

failover replication rate conns

Example:


ciscoasa(config)# failover replication rate 20000

The minimum and maximum rate is determined by your model. The default is the maximum rate. In Active/Active mode, you set this rate for the system; you cannot set this rate per failover group.

Step 5

Disable the ability to make any configuration changes directly on the standby unit or context:

failover standby config-lock

By default, configurations on the standby unit/context are allowed with a warning message.

Step 6

(Active/Active mode only) Specify the failover group you want to customize:

failover group {1 | 2}

Example:


ciscoasa(config)# failover group 1
ciscoasa(config-fover-group)#

Step 7

Enable HTTP state replication:

  • For Active/Standby mode:

    failover replication http

  • For Active/Active mode:

    replication http

To allow HTTP connections to be included in the state information replication, you need to enable HTTP replication. We recommend enabling HTTP state replication.

Note

 

Because of a delay when deleting HTTP flows from the standby unit when using failover, the show conn count output might show different numbers on the active unit vs. the standby unit; if you wait several seconds and re-issue the command, you will see the same count on both units.

Step 8

Set the threshold for failover when interfaces fail:

  • For Active/Standby mode:

    failover interface-policy num [%]

    Example: 

    
ciscoasa (config)# failover interface-policy 20%

  • For Active/Active mode:

    interface-policy num [%]

    Example: 

    
ciscoasa(config-fover-group)# interface-policy 20%

By default, one interface failure causes failover.

When specifying a specific number of interfaces, the num argument can be from 1 to 1025.

When specifying a percentage of interfaces, the num argument can be from 1 to 100.

Step 9

Change the interface poll and hold times:

  • For Active/Standby mode:

    failover polltime interface [msec] polltime [holdtime time]

    Example: 

    
ciscoasa(config)# failover polltime interface msec 500 holdtime 5

  • For Active/Active mode:

    polltime interface [msec] polltime [holdtimetime]

    Example: 

    
ciscoasa(config-fover-group)# polltime interface msec 500 holdtime 5

  • polltime —Sets how long to wait between sending a hello packet to the peer. Valid values for the polltime are from 1 to 15 seconds or, if the optional msec keyword is used, from 500 to 999 milliseconds. The default is 5 seconds.

  • holdtimetime —Sets the time (as a calculation) between the last-received hello message from the peer unit and the commencement of interface tests to determine the health of the interface. It also sets the duration of each interface test as holdtime/16. Valid values are from 5 to 75 seconds. The default is 5 times the polltime. You cannot enter a holdtime value that is less than five times the polltime.

    To calculate the time before starting interface tests (y):

    1. x = (holdtime/polltime)/2, rounded to the nearest integer. (.4 and down rounds down; .5 and up rounds up.)

    2. y = x*polltime

    For example, if you use the default holdtime of 25 and polltime of 5, then y = 15 seconds.

Step 10

Configure the virtual MAC address for an interface:

  • For Active/Standby mode:

    failover mac address phy_if active_mac standby_mac

    Example: 

    
ciscoasa(config)# failover mac address gigabitethernet0/2 00a0.c969.87c8 00a0.c918.95d8

  • For Active/Active mode:

    mac address phy_if active_mac standby_mac

    Example: 

    
ciscoasa(config-fover-group)# mac address gigabitethernet0/2 00a0.c969.87c8 00a0.c918.95d8

The phy_if argument is the physical name of the interface, such as gigabitethernet0/1.

The active_mac and standby_mac arguments are MAC addresses in H.H.H format, where H is a 16-bit hexadecimal digit. For example, the MAC address 00-0C-F1-42-4C-DE would be entered as 000C.F142.4CDE.

The active_mac address is associated with the active IP address for the interface, and the standby_mac is associated with the standby IP address for the interface.

You can also set the MAC address using other commands or methods, but we recommend using only one method. If you set the MAC address using multiple methods, the MAC address used depends on many variables, and might not be predictable.

Use the show interface command to display the MAC address used by an interface.

Step 11

(Active/Active mode only) Repeat this procedure for the other failover group.

Configure Interface Monitoring

By default, monitoring is enabled on all physical interfaces, or for the Firepower 1010, all VLAN interfaces. Firepower 1010 switch ports are not elegible for interface monitoring.

You might want to exclude interfaces attached to less critical networks from affecting your failover policy.

You can monitor up to 1025 interfaces on a unit (across all contexts in multiple context mode).

Before you begin

In multiple context mode, configure interfaces within each context.

Procedure

Enable or disable health monitoring for an interface:

[no] monitor-interface {if_name}

Example:


ciscoasa(config)# monitor-interface inside
ciscoasa(config)# no monitor-interface eng1

Configure Support for Asymmetrically Routed Packets (Active/Active Mode)

When running in Active/Active failover, a unit might receive a return packet for a connection that originated through its peer unit. Because the ASA that receives the packet does not have any connection information for the packet, the packet is dropped. This drop most commonly occurs when the two ASAs in an Active/Active failover pair are connected to different service providers and the outbound connection does not use a NAT address.

You can prevent the return packets from being dropped by allowing asymmetrically routed packets. To do so, you assign the similar interfaces on each ASA to the same ASR group. For example, both ASAs connect to the inside network on the inside interface, but connect to separate ISPs on the outside interface. On the primary unit, assign the active context outside interface to ASR group 1; on the secondary unit, assign the active context outside interface to the same ASR group 1. When the primary unit outside interface receives a packet for which it has no session information, it checks the session information for the other interfaces in standby contexts that are in the same group; in this case, ASR group 1. If it does not find a match, the packet is dropped. If it finds a match, then one of the following actions occurs:

  • If the incoming traffic originated on a peer unit, some or all of the layer 2 header is rewritten and the packet is redirected to the other unit. This redirection continues as long as the session is active.

  • If the incoming traffic originated on a different interface on the same unit, some or all of the layer 2 header is rewritten and the packet is reinjected into the stream.


Note

This feature does not provide asymmetric routing; it restores asymmetrically routed packets to the correct interface.

The following figure shows an example of an asymmetrically routed packet.

Figure 6. ASR Example

  1. An outbound session passes through the ASA with the active SecAppA context. It exits interface outside ISP-A (192.168.1.1).

  2. Because of asymmetric routing configured somewhere upstream, the return traffic comes back through the interface outsideISP-B (192.168.2.2) on the ASA with the active SecAppB context.

  3. Normally the return traffic would be dropped because there is no session information for the traffic on interface 192.168.2.2. However, the interface is configured as part of ASR group 1. The unit looks for the session on any other interface configured with the same ASR group ID.

  4. The session information is found on interface outsideISP-A (192.168.1.2), which is in the standby state on the unit with SecAppB. Stateful Failover replicated the session information from SecAppA to SecAppB.

  5. Instead of being dropped, the layer 2 header is rewritten with information for interface 192.168.1.1 and the traffic is redirected out of the interface 192.168.1.2, where it can then return through the interface on the unit from which it originated (192.168.1.1 on SecAppA). This forwarding continues as needed until the session ends.

Before you begin

  • Stateful Failover—Passes state information for sessions on interfaces in the active failover group to the standby failover group.

  • Replication HTTP—HTTP session state information is not passed to the standby failover group, and therefore is not present on the standby interface. For the ASA to be able to re-route asymmetrically routed HTTP packets, you need to replicate the HTTP state information.

  • Perform this procedure within each active context on the primary and secondary units.

  • You cannot configure both ASR groups and traffic zones within a context. If you configure a zone in a context, none of the context interfaces can be part of an ASR group.

Procedure

Step 1

On the primary unit, specify the interface for which you want to allow asymmetrically routed packets:

interface phy_if

Example:


primary/admin(config)# interface gigabitethernet 0/0

Step 2

Set the ASR group number for the interface:

asr-group num

Example:


primary/admin(config-ifc)# asr-group 1

Valid values for num range from 1 to 32.

Step 3

On the secondary unit, specify the similar interface for which you want to allow asymmetrically routed packets:

interface phy_if

Example:


secondary/ctx1(config)# interface gigabitethernet 0/1

Step 4

Set the ASR group number for the interface to match the primary unit interface:

asr-group num

Example:


secondary/ctx1(config-ifc)# asr-group 1

Examples

The two units have the following configuration (configurations show only the relevant commands). The device labeled SecAppA in the diagram is the primary unit in the failover pair.

Primary Unit System Configuration 


interface GigabitEthernet0/1
  description LAN/STATE Failover Interface
interface GigabitEthernet0/2
  no shutdown
interface GigabitEthernet0/3
  no shutdown
interface GigabitEthernet0/4
  no shutdown
interface GigabitEthernet0/5
  no shutdown
failover
failover lan unit primary
failover lan interface folink GigabitEthernet0/1
failover link folink
failover interface ip folink 10.0.4.1 255.255.255.0 standby 10.0.4.11
failover group 1
  primary
failover group 2
  secondary
admin-context SecAppA
context admin
  allocate-interface GigabitEthernet0/2
  allocate-interface GigabitEthernet0/3
  config-url flash:/admin.cfg
  join-failover-group 1
context SecAppB
  allocate-interface GigabitEthernet0/4
  allocate-interface GigabitEthernet0/5
  config-url flash:/ctx1.cfg
  join-failover-group 2

SecAppA Context Configuration 


interface GigabitEthernet0/2
  nameif outsideISP-A
  security-level 0
  ip address 192.168.1.1 255.255.255.0 standby 192.168.1.2
  asr-group 1
interface GigabitEthernet0/3
  nameif inside
  security-level 100
  ip address 10.1.0.1 255.255.255.0 standby 10.1.0.11
monitor-interface outside

SecAppB Context Configuration 


interface GigabitEthernet0/4
  nameif outsideISP-B
  security-level 0
  ip address 192.168.2.2 255.255.255.0 standby 192.168.2.1
  asr-group 1
interface GigabitEthernet0/5
  nameif inside
  security-level 100
  ip address 10.2.20.1 255.255.255.0 standby 10.2.20.11

Manage Failover

This section describes how to manage Failover units after you enable Failover, including how to change the Failover setup and how to force failover from one unit to another.

Force Failover

To force the standby unit to become active, perform the following procedure.

Before you begin

In multiple context mode, perform this procedure in the System execution space.

Procedure

Step 1

Force a failover when entered on the standby unit. The standby unit becomes the active unit.

If you specify the group group_id, then this command forces a failover when entered on the standby unit for the specified Active/Active failover group. The standby unit becomes the active unit for the failover group.

  • For Active/Standby mode on the standby unit:

    failover active

  • For Active/Active mode on the standby unit:

    failover active [group group_id]

    Example: 

    
standby# failover active group 1

Step 2

Force a failover when entered on the active unit. The active unit becomes the standby unit.

If you specify the group group_id, then this command forces a failover when entered on the active unit for the specified failover group. The active unit becomes the standby unit for the failover group.

  • For Active/Standby mode on the active unit:

    no failover active

  • For Active/Active mode on the active unit:

    no failover active [group group_id]

    Example: 

    
active# no failover active group 1

Disable Failover

Disabling failover on one or both units causes the active and standby state of each unit to be maintained until you reload. For an Active/Active failover pair, the failover groups remain in the active state on whichever unit they are active, no matter which unit they are configured to prefer.

See the following characteristics when you disable failover:

  • The standby unit/context remains in standby mode so that both units do not start passing traffic (this is called a pseudo-standby state).

  • The standby unit/context continues to use its standby IP addresses even though it is no longer connected to an active unit/context.

  • The standby unit/context continues to listen for a connection on the failover link. If failover is re-enabled on the active unit/context, then the standby unit/context resumes ordinary standby status after re-synchronizing the rest of its configuration.

  • Do not enable failover manually on the standby unit to make it active; instead see Force Failover. If you enable failover on the standby unit, you will see a MAC address conflict that can disrupt IPv6 traffic.

  • To truly disable failover, save the no failover configuration to the startup configuration, and then reload.

Before you begin

In multiple context mode, perform this procedure in the system execution space.

Procedure

Step 1

Disable failover:

no failover

Step 2

To completely disable failover, save the configuration and reload:

write memory

reload

Restore a Failed Unit

To restore a failed unit to an unfailed state, perform the following procedure.

Before you begin

In multiple context mode, perform this procedure in the System execution space.

Procedure

Step 1

Restore a failed unit to an unfailed state:

  • For Active/Standby mode:

    failover reset

  • For Active/Active mode:

    failover reset [group group_id]

    Example: 

    
ciscoasa(config)# failover reset group 1

Restoring a failed unit to an unfailed state does not automatically make it active; restored units remain in the standby state until made active by failover (forced or natural). An exception is a failover group (Active/Active mode only) configured with failover preemption. If previously active, a failover group becomes active if it is configured with preemption and if the unit on which it failed is the preferred unit.

If you specify the group group_id, this command restores a failed Active/Active failover group to an unfailed state.

Step 2

(Active/Active mode only) To reset failover at the failover group level:

  1. In the System choose Monitoring > Failover > Failover Group #, where # is the number of the failover group you want to control.

  2. Click Reset Failover.

Re-Sync the Configuration

If you enter the write standby command on the active unit, the standby unit clears its running configuration (except for the failover commands used to communicate with the active unit), and the active unit sends its entire configuration to the standby unit.

For multiple context mode, when you enter the write standby command in the system execution space, all contexts are replicated. If you enter the write standby command within a context, the command replicates only the context configuration.

Replicated commands are stored in the running configuration.

Test the Failover Functionality

To test failover functionality, perform the following procedure.

Procedure

Step 1

Test that your active unit is passing traffic as expected by using FTP (for example) to send a file between hosts on different interfaces.

Step 2

Force a failover by entering the following command on the active unit:

Active/Standby mode:

ciscoasa(config)# no failover active

Active/Active mode:

ciscoasa(config)# no failover active group group_id

Step 3

Use FTP to send another file between the same two hosts.

Step 4

If the test was not successful, enter the show failover command to check the failover status.

Step 5

When you are finished, you can restore the unit to active status by enter the following command on the newly active unit:

Active/Standby mode:

ciscoasa(config)# no failover active

Active/Active mode:

ciscoasa(config)# failover active group group_id

Note

 

When an ASA interface goes down, for failover it is still considered to be a unit issue. If the ASA detects that an interface is down, failover occurs immediately, without waiting for the interface holdtime. The interface holdtime is only useful when the ASA considers its status to be OK, although it is not receiving hello packets from the peer. To simulate interface holdtime, shut down the VLAN on the switch to prevent peers from receiving hello packets from each other.

Remote Command Execution

Remote command execution lets you send commands entered at the command line to a specific failover peer.

Send a Command

Because configuration commands are replicated from the active unit or context to the standby unit or context, you can use the failover exec command to enter configuration commands on the correct unit, no matter which unit you are logged in to. For example, if you are logged in to the standby unit, you can use the failover exec active command to send configuration changes to the active unit. Those changes are then replicated to the standby unit. Do not use the failover exec command to send configuration commands to the standby unit or context; those configuration changes are not replicated to the active unit and the two configurations will no longer be synchronized.

Output from configuration, exec, and show commands is displayed in the current terminal session, so you can use the failover exec command to issue show commands on a peer unit and view the results in the current terminal.

You must have sufficient privileges to execute a command on the local unit to execute the command on the peer unit.

Procedure

Step 1

If you are in multiple context mode, use the changeto contextname command to change to the context you want to configure. You cannot change contexts on the failover peer with the failover exec command.

Step 2

Use the following command to send commands to he specified failover unit:

ciscoasa(config)# failover exec {active | mate | standby}

Use the active or standby keyword to cause the command to be executed on the specified unit, even if that unit is the current unit. Use the mate keyword to cause the command to be executed on the failover peer.

Commands that cause a command mode change do not change the prompt for the current session. You must use the show failover exec command to display the command mode the command is executed in. See Change Command Modes, page 7-53 for more information.

Change Command Modes

The failover exec command maintains a command mode state that is separate from the command mode of your terminal session. By default, the failover exec command mode starts in global configuration mode for the specified device. You can change that command mode by sending the appropriate command (such as the interface command) using the failover exec command. The session prompt does not change when you change modes using failover exec .

For example, if you are logged into global configuration mode of the active unit of a failover pair, and you use the failover exec active command to change to interface configuration mode, the terminal prompt remains in global configuration mode, but commands entered using failover exec are entered in interface configuration mode.

The following examples show the difference between the terminal session mode and the failover exec command mode. In the example, the administrator changes the failover exec mode on the active unit to interface configuration mode for the interface GigabitEthernet0/1. After that, all commands entered using failover exec active are sent to interface configuration mode for interface GigabitEthernet0/1. The administrator then uses failover exec active to assign an IP address to that interface. Although the prompt indicates global configuration mode, the failover exec active mode is in interface configuration mode. 


ciscoasa(config)# failover exec active interface GigabitEthernet0/1
ciscoasa(config)# failover exec active ip address 192.168.1.1 255.255.255.0 standby 192.168.1.2
ciscoasa(config)# router rip 
ciscoasa(config-router)#

Changing commands modes for your current session to the device does not affect the command mode used by the failover exec command. For example, if you are in interface configuration mode on the active unit, and you have not changed the failover exec command mode, the following command would be executed in global configuration mode. The result would be that your session to the device remains in interface configuration mode, while commands entered using failover exec active are sent to router configuration mode for the specified routing process. 


ciscoasa(config-if)# failover exec active router ospf 100
ciscoasa(config-if)#

Use the show failover exec command to display the command mode on the specified device in which commands sent with the failover exec command are executed. The show failover exec command takes the same keywords as the failover exec command: active , mate , or standby . The failover exec mode for each device is tracked separately.

For example, the following is sample output from the show failover exec command entered on the standby unit: 


ciscoasa(config)# failover exec active interface GigabitEthernet0/1
ciscoasa(config)# sh failover exec active
Active unit Failover EXEC is at interface sub-command mode

ciscoasa(config)# sh failover exec standby
Standby unit Failover EXEC is at config mode

ciscoasa(config)# sh failover exec mate
Active unit Failover EXEC is at interface sub-command mode

Security Considerations

The failover exec command uses the failover link to send commands to and receive the output of the command execution from the peer unit. You should enable encryption on the failover link to prevent eavesdropping or man-in-the-middle attacks.

Limitations of Remote Command Execution

When you use remote commands, you face the following limitations:

  • If you upgrade one unit using the zero-downtime upgrade procedure and not the other, both units must be running software that supports the failover exec command.

  • Command completion and context help is not available for the commands in the cmd_string argument.

  • In multiple context mode, you can only send commands to the peer context on the peer unit. To send commands to a different context, you must first change to that context on the unit to which you are logged in.

  • You cannot use the following commands with the failover exec command:

    • changeto

    • debug (undebug)

  • If the standby unit is in the failed state, it can still receive commands from the failover exec command if the failure is due to a service card failure; otherwise, the remote command execution will fail.

  • You cannot use the failover exec command to switch from privileged EXEC mode to global configuration mode on the failover peer. For example, if the current unit is in privileged EXEC mode, and you enter failover exec mate configure terminal , the show failover exec mate output will show that the failover exec session is in global configuration mode. However, entering configuration commands for the peer unit using failover exec will fail until you enter global configuration mode on the current unit.

  • You cannot enter recursive failover exec commands, such as the failover exec mate failover exec mate command.

  • Commands that require user input or confirmation must use the noconfirm option. For example, to reload the mate, enter:

    failover exec mate reload noconfirm

Monitoring Failover

This section lets you monitor the Failover status.

Failover Messages

When a failover occurs, both ASAs send out system messages.

Failover Syslog Messages

The ASA issues a number of syslog messages related to failover at priority level 2, which indicates a critical condition. To view these messages, see the syslog messages guide. The ranges of message IDs associated with failover are: 101xxx, 102xxx, 103xxx, 104xxx, 105xxx, 210xxx, 311xxx, 709xxx, 727xxx. For example, 105032 and 105043 indicate a problem with the failover link.


Note

During failover, the ASA logically shuts down and then brings up interfaces, generating syslog messages 411001 and 411002. This is normal activity.

Failover Debug Messages

To see debug messages, enter the debug fover command. See the command reference for more information.


Note

Because debugging output is assigned high priority in the CPU process, it can drastically affect system performance. For this reason, use the debug fover commands only to troubleshoot specific problems or during troubleshooting sessions with Cisco TAC.

SNMP Failover Traps

To receive SNMP syslog traps for failover, configure the SNMP agent to send SNMP traps to SNMP management stations, define a syslog host, and compile the Cisco syslog MIB into your SNMP management station.

Monitoring Failover Status

To monitor failover status, enter one of the following commands:

  • show failover

    Displays information about the failover state of the unit.

  • show failover group

    Displays information about the failover state of the failover group. The information displayed is similar to that of the show failover command but limited to the specified group.

  • show monitor-interface

    Displays information about the monitored interface.

  • show running-config failover

    Displays the failover commands in the running configuration.

History for Failover

Feature Name

Releases

Feature Information

Active/Standby failover

7.0(1)

This feature was introduced.

Active/Active failover

7.0(1)

This feature was introduced.

Support for a hex value for the failover key

7.0(4)

You can now specify a hex value for failover link encryption.

We modified the following command: failover key hex.

Support for the master passphrase for the failover key

8.3(1)

The failover key now supports the master passphrase, which encrypts the shared key in the running and startup configuration. If you are copying the shared secret from one ASA to another, for example from the more system:running-config command, you can successfully copy and paste the encrypted shared key.

Note

 

The failover key shared secret shows as ***** in show running-config output; this obscured key is not copyable.

We modified the following command: failover key [0 | 8].

IPv6 support for failover added.

8.2(2)

We modified the following commands: failover interface ip , show failover , ipv6 address , show monitor-interface .

Change to failover group unit preference during "simultaneous" bootup.

9.0(1)

Earlier software versions allowed “simultaneous” boot up so that the failover groups did not require the preempt command to become active on the preferred unit. However, this functionality has now changed so that both failover groups become active on the first unit to boot up.

Support for IPsec LAN-to-LAN tunnels to encrypt failover and state link communications

9.1(2)

Instead of using the proprietary encryption for the failover key (the failover key command), you can now use an IPsec LAN-to-LAN tunnel for failover and state link encryption.

Note

 

Failover LAN-to-LAN tunnels do not count against the IPsec (Other VPN) license.

We introduced or modified the following commands: failover ipsec pre-shared-key, show vpn-sessiondb.

Disable health monitoring of a hardware module

9.3(1)

By default, the ASA monitors the health of an installed hardware module such as the ASA FirePOWER module. If you do not want a hardware module failure to trigger failover, you can disable module monitoring.

We modified the following command: monitor-interface service-module

Lock configuration changes on the standby unit or standby context in a failover pair

9.3(2)

You can now lock configuration changes on the standby unit (Active/Standby failover) or the standby context (Active/Active failover) so you cannot make changes on the standby unit outside normal configuration syncing.

We introduced the following command: failover standby config-lock

Enable use of the Management 1/1 interface as the failover link on the ASA 5506H

9.5(1)

On the ASA 5506H only, you can now configure the Management 1/1 interface as the failover link. This feature lets you use all other interfaces on the device as data interfaces. Note that if you use this feature, you cannot use the ASA Firepower module, which requires the Management 1/1 interface to remain as a regular management interface.

We modified the following commands: failover lan interface, failover link

Carrier Grade NAT enhancements now supported in failover and ASA clustering

9.5(2)

For carrier-grade or large-scale PAT, you can allocate a block of ports for each host, rather than have NAT allocate one port translation at a time (see RFC 6888). This feature is now supported in failover and ASA cluster deployments.

We modified the following command: show local-host

Improved sync time for dynamic ACLs from Secure Client when using Active/Standby failover

9.6(2)

When you use Secure Client on a failover pair, then the sync time for the associated dynamic ACLs (dACLs) to the standby unit is now improved. Previously, with large dACLs, the sync time could take hours during which time the standby unit is busy syncing instead of providing high availability backup.

We did not modify any commands.

Stateful failover for Secure Client connections in multiple context mode

9.6(2)

Stateful failover is now supported for Secure Client connections in multiple context mode.

We did not modify any commands.

Interface link state monitoring polling for failover now configurable for faster detection

9.7(1)

By default, each ASA in a failover pair checks the link state of its interfaces every 500 msec. You can now configure the polling interval, between 300 msec and 799 msec; for example, if you set the polltime to 300 msec, the ASA can detect an interface failure and trigger failover faster.

We introduced the following command: failover polltime link-state

Bidirectional Forwarding Detection (BFD) support for Active/Standby failover health monitoring on the Firepower 9300 and 4100

9.7(1)

You can enable Bidirectional Forwarding Detection (BFD) for the failover health check between two units of an Active/Standby pair on the Firepower 9300 and 4100. Using BFD for the health check is more reliable than the default health check method and uses less CPU.

We introduced the following command: failover health-check bfd

Disable failover delay

9.15(1)

When you use bridge groups or IPv6 DAD, when a failover occurs the new active unit waits up to 3000 ms for the standby unit to finish networking tasks and transition to the standby state. Then the active unit can start passing traffic. To avoid this delay, you can disable the waiting time, and the active unit will start passing traffic before the standby unit transitions.

New/Modified commands: failover wait-disable

Config-Sync Optimization feature for faster HA peering

9.18(1)

The Config-Sync Optimization feature enables comparing the configuration of the joining unit and the active unit by exchanging config-hash values. If the hash computed on both active and joining units match, the joining unit skips full config-sync and rejoin the HA. This feature enables faster HA peering and reduces maintenance window and upgrade time.