Table Of Contents
MPLS Traffic Engineering—RSVP Hello State Timer
Prerequisites for MPLS Traffic Engineering—RSVP Hello State Timer
Restrictions for MPLS Traffic Engineering—RSVP Hello State Timer
Information About MPLS Traffic Engineering—RSVP Hello State Timer
Benefits of MPLS Traffic Engineering—RSVP Hello State Timer
How to Configure MPLS Traffic Engineering—RSVP Hello State Timer
Enabling the Hello State Timer Globally
Enabling the Hello State Timer on an Interface
Setting a DSCP Value on an Interface
Setting a Hello Request Interval on an Interface
Setting a Missed Refresh Limit on an Interface
Verifying Hello for State Timer Configuration
Sample Configurations for Troubleshooting
Configuration Examples for MPLS Traffic Engineering—RSVP Hello State Timer
MPLS Traffic Engineering—RSVP Hello State Timer: Example
ip rsvp signalling hello refresh interval
ip rsvp signalling hello refresh misses
ip rsvp signalling hello reroute dscp
ip rsvp signalling hello reroute refresh interval
ip rsvp signalling hello reroute refresh misses
MPLS Traffic Engineering—RSVP Hello State Timer
First Published: August 2, 2004Last Updated: June 29, 2007The MPLS Traffic Engineering—RSVP Hello State Timer feature detects when a neighbor is down and triggers faster state timeout thereby freeing resources such as bandwidth to be reused by other label-switched paths (LSPs).
History for the MPLS Traffic Engineering—RSVP Hello State Timer Feature
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Contents
•Prerequisites for MPLS Traffic Engineering—RSVP Hello State Timer
•Restrictions for MPLS Traffic Engineering—RSVP Hello State Timer
•Information About MPLS Traffic Engineering—RSVP Hello State Timer
•How to Configure MPLS Traffic Engineering—RSVP Hello State Timer
•Configuration Examples for MPLS Traffic Engineering—RSVP Hello State Timer
•ip rsvp signalling hello dscp
Prerequisites for MPLS Traffic Engineering—RSVP Hello State Timer
•Configure Resource Reservation Protocol (RSVP) on routers.
•Enable Multiprotocol Label Switching (MPLS).
•Configure traffic engineering (TE) on routers.
•Enable hellos for state timeout.
Restrictions for MPLS Traffic Engineering—RSVP Hello State Timer
•Hellos for state timeout are dependent on graceful restart, if it is configured; however, graceful restart is independent of hellos for state timeout.
•Unnumbered interfaces are not supported.
•Hellos for state timeout are configured on a per-interface basis.
Information About MPLS Traffic Engineering—RSVP Hello State Timer
To configure MPLS TE—RSVP Hello State Timer, you should understand the following concepts:
•Benefits of MPLS Traffic Engineering—RSVP Hello State Timer
Hellos for State Timeout
When RSVP signals a TE LSP and there is a failure somewhere along the path, the failure can remain undetected for as long as two minutes. During this time, bandwidth is held by the non-functioning LSP on the nodes downstream from the point of failure along the path with the state intact. If this bandwidth is needed by headend tunnels to signal or resignal LSPs, tunnels may fail to come up for several minutes thereby negatively affecting convergence time.
Hellos enable RSVP nodes to detect when a neighboring node is not reachable. After a certain number of intervals, hellos notice that a neighbor is not responding and delete its state. This action frees the node's resources to be reused by other LSPs.
Hellos must be configured both globally on the router and on the specific interface to be operational.
NonFast-Reroutable TE LSP
As shown in Figure 1, a nonfast-reroutable TE LSP exists from Router 1 to Router 3 via Router 2.
Figure 1 NonFast-Reroutable TE LSP
Assume that the link between Router 1 and Router 2 fails. This type of problem can be detected by various means including interface failure, Interior Gateway Protocol (IGP) (Open Shortest Path First (OSPF) or Intermediate System-to-Intermediate System (IS-IS)), and RSVP hellos. However, sometimes interface failure cannot be detected; for example, when Router 1 and Router 2 are interconnected through a Layer 2 switch. The IGP may be slow detecting the failure. Or there may be no IGP running between Router 1 and Router 2; for example, between two Autonomous System Boundary routers (ASBRs) interconnecting two autonomous systems.
If hellos were running between Router 1 and Router 2, they would notice that communication was lost and time out the state immediately.
Router 2 sends a delayed PathTear message to Router 3 so that the state can be deleted on all nodes thereby speeding up the convergence time.
Note The PathTear message is delayed one second because on some platforms data is being forwarded even after the control plane is down.
Router 1 sends a destructive PathError message upstream to Router 0 with error code ROUTING_PROBLEM and error value NO_ROUTE.
LSP1 goes from Router 0 to Router 1 to Router 2 to Router 3; LSP 2 goes from Router 0 to Router 1 to Router 4 to Router 2 to Router 3.
Hello Instance
A hello instance implements RSVP hellos for a given router interface address and a remote IP address. A hello instance is expensive because of the large number of hello requests that are sent and the strains they put on the router resources. Therefore, you should create a hello instance only when it is needed to time out state and delete the hello instance when it is no longer necessary.
Benefits of MPLS Traffic Engineering—RSVP Hello State Timer
Faster Network Convergence
RSVP hellos can be used to detect when a neighboring node is down. The hello state timer then triggers a state timeout. As a result, network convergence time is reduced, and nodes can forward traffic on alternate paths or assist in stateful switchover (SSO) operation.
How to Configure MPLS Traffic Engineering—RSVP Hello State Timer
This section contains the following procedures:
Note The following commands also enable Fast Reroute; however, this section focuses on the RSVP hello state timer.
•Enabling the Hello State Timer Globally (required)
•Enabling the Hello State Timer on an Interface (required)
•Setting a DSCP Value on an Interface (optional)
•Setting a Hello Request Interval on an Interface (optional)
•Setting a Missed Refresh Limit on an Interface (optional)
•Verifying Hello for State Timer Configuration (optional)
Enabling the Hello State Timer Globally
Perform this task to enable the RSVP hello state timer globally.
SUMMARY STEPS
1. enable
2. configure terminal
3. ip rsvp signalling hello
4. end
DETAILED STEPS
Enabling the Hello State Timer on an Interface
Perform this task to enable the hello state timer on an interface.
SUMMARY STEPS
1. enable
2. configure terminal
3. interface type number
4. ip rsvp signalling hello
5. end
DETAILED STEPS
Setting a DSCP Value on an Interface
Perform this task to set a DSCP value on an interface.
SUMMARY STEPS
1. enable
2. configure terminal
3. interface type number
4. ip rsvp signalling hello reroute dscp num
5. end
DETAILED STEPS
Setting a Hello Request Interval on an Interface
Perform this task to set a hello request interval on an interface.
SUMMARY STEPS
1. enable
2. configure terminal
3. interface type number
4. ip rsvp signalling hello reroute refresh interval interval-value
5. end
DETAILED STEPS
Setting a Missed Refresh Limit on an Interface
Perform this task to set a missed refresh limit on an interface.
SUMMARY STEPS
1. enable
2. configure terminal
3. interface type number
4. ip rsvp signalling hello reroute refresh misses msg-count
5. end
DETAILED STEPS
Verifying Hello for State Timer Configuration
Perform this task to verify the hello for state timer configuration.
SUMMARY STEPS
1. enable
2. show ip rsvp hello
DETAILED STEPS
Sample Configurations for Troubleshooting
Fast-Reroutable TE LSP with Backup Tunnel
As shown in Figure 2, a fast reroutable TE LSP with a backup tunnel exists from Router1 to Router 2 to Router 3.
Figure 2 Fast Reroutable TE LSP with Backup Tunnel
This TE LSP has a backup tunnel from Router 1 to Router 3 protecting the fast reroutable TE LSP against a failure in the Router 1-Router 2 link and node Router 2. However, assume that a failure occurs in the link connecting Router 1 to Router 2.
If hellos were running between Router 1 and Router 2, they would notice that the link is down, but would not time out the state. Router 2 notices the failure, but cannot time out the TE LSP because Router 2 may be a merge point or another downstream node may be a merge point. Router 1 notices the failure and switches to the backup LSP; however, Router 1 cannot time out the state either.
Note A hello instance is not created in the preceding scenario because the neighbor is down and the hello instance cannot take action.
Fast-Reroutable TE LSP Without Backup Tunnel
As shown in Figure 3, a fast-reroutable TE LSP without a backup tunnel exists from Router 1, the point of local repair (PLR), to Router 2 to Router 3.
Figure 3 Fast Reroutable TE LSP Without Backup Tunnel
Assume that a failure occurs in the link connecting Router 1 to Router 3. Router 1 can time out the state for the TE LSP because Router 1 knows there is no backup tunnel. However, Router 2 cannot time out the state because Router 2 does not know whether a backup tunnel exists. Also, Router 2 may be a merge point, and therefore, cannot time out the state.
Note A hello instance is not created in the preceding scenario because the neighbor is down and the hello instance cannot take action.
Hello Instance
•On a fast-reroutable TE LSP with no backup tunnel, create a hello instance with the neighbor downstream (next hop (NHOP)).
•On a non-fast-reroutable TE LSP, create a hello instance with the neighbor downstream (NHOP) and the neighbor upstream (previous hop (PHOP)). This is in addition to the existing hellos for Fast Reroute.
Note If both Fast Reroute and hellos for state timeout hello instances are needed on the same link, only one hello instance is created. It will have the Fast Reroute configuration including interval, missed refreshes, and DSCP. When a neighbor is down, Fast Reroute and the hello state timer take action.
Configuration Examples for MPLS Traffic Engineering—RSVP Hello State Timer
This section provides a configuration example for the MPLS TE—RSVP Hello State Timer feature:
•MPLS Traffic Engineering—RSVP Hello State Timer: Example
MPLS Traffic Engineering—RSVP Hello State Timer: Example
In the following example, the hello state timer is enabled globally and on an interface; and related parameters, including a DSCP value, a refresh interval, and a missed refresh limit are set on an interface.
Router# configure terminalEnter configuration commands, one per line. End with CNTL/Z.Router(config)# ip rsvp signalling helloRouter(config)# interface Ethernet 0/0Router(config-if)# ip rsvp signalling helloRouter(config-if)# ip rsvp signalling hello reroute dscp 30Router(config-if)# ip rsvp signalling hello reroute refresh interval 5000Router(config-if)# ip rsvp signalling hello reroute refresh misses 5Router(config-if)# endThe following example verifies the status of the hello state timer (reroute):
Router# show ip rsvp helloHello:Fast-Reroute/Reroute:EnabledStatistics:EnabledGraceful Restart:Enabled (help-neighbor only)Additional References
The following sections provide references related to the MPLS Traffic Engineering—RSVP Hello State Timer feature.
Related Documents
Related Topic Document TitleRSVP commands: complete command syntax, command mode, defaults, usage guidelines, and examples
Cisco IOS Quality of Service Solutions Command Reference, Release 12.2SX
Cisco IOS Quality of Service Solutions Command Reference, Release 12.2SR
QoS features including signaling, classification, and congestion management
Cisco IOS Quality of Service Solutions Configuration Guide, Release 12.4
Stateful Switchover
Stateful Switchover feature module
MPLS Label Distribution Protocol
MPLS Label Distribution Protocol (LDP) feature module
Cisco nonstop forwarding
Cisco Nonstop Forwarding feature module
Information on backup tunnels, link and node failures, RSVP hellos
MPLS Traffic Engineering (TE)—Link and Node Protection, with RSVP Hellos Support feature module
Information on stateful switchover, Cisco nonstop forwarding, graceful restart
Standards
Standard TitleNo new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.
—
MIBs
RFCs
Technical Assistance
Command Reference
This section documents only commands that are new or modified.
•ip rsvp signalling hello dscp
•ip rsvp signalling hello refresh interval
•ip rsvp signalling hello refresh misses
•ip rsvp signalling hello reroute dscp
•ip rsvp signalling hello reroute refresh interval
•ip rsvp signalling hello reroute refresh misses
ip rsvp signalling hello dscp
To set the differentiated services code point (DSCP) value that is in the IP header of a Resource Reservation Protocol (RSVP) traffic engineering (TE) hello message sent from an interface, use the ip rsvp signalling hello dscp command in interface configuration mode. To set the DSCP to its default value, use the no form of this command.
ip rsvp signalling hello [fast-reroute] dscp num
no ip rsvp signalling hello [fast-reroute] dscp
Syntax Description
fast-reroute
(Optional) Initiates Fast Reroute capability.
num
DSCP value. Valid values are from 0 to 63.
Defaults
The default DSCP value is 48.
Command Modes
Interface configuration
Command History
Usage Guidelines
If a link is congested, you should set the DSCP to a value higher than 0 to reduce the likelihood that hello messages get dropped.
You configure the DSCP per interface, not per flow.
The DSCP applies to the RSVP hellos created on a specific interface. You can configure each interface independently for DSCP.
If you issue the ip rsvp signalling hello dscp command without the optional fast-reroute keyword, the command applies to Fast Reroute hellos. This command is provided for backward compatibility; however, we recommend that you use the ip rsvp signalling hello fast-reroute dscp command.
Examples
In the following example, hello messages sent from this interface have a DSCP value of 30 and Fast Reroute capability is enabled by specifying the fast-reroute keyword:
Router(config-if)# ip rsvp signalling hello fast-reroute dscp 30In the following example, hello messages sent from this interface have a DSCP value of 30 and Fast Reroute capability is enabled by default:
Router(config-if)# ip rsvp signalling hello dscp 30Related Commands
ip rsvp signalling hello refresh interval
To configure the Resource Reservation Protocol (RSVP) traffic engineering (TE) hello refresh interval, use the ip rsvp signalling hello refresh interval command in interface configuration mode. To set the refresh interval to its default value, use the no form of the command.
ip rsvp signalling hello [fast-reroute] refresh interval interval-value
no ip rsvp signalling hello [fast-reroute] refresh interval
Syntax Description
Defaults
10000 milliseconds (10 seconds)
Command Modes
Interface configuration
Command History
Usage Guidelines
You can configure the hello request interval on a per-interface basis. A node periodically generates a hello message containing a Hello Request object for each neighbor whose status is being tracked. The frequency of those hello messages is determined by the hello interval.
If you issue the ip rsvp signalling hello refresh interval command without the optional fast-reroute keyword, the command applies to Fast Reroute hellos. This command is provided for backward compatibility; however, we recommend that you use the ip rsvp signalling hello fast-reroute refresh interval command.
Examples
In the following example, hello requests are sent to a neighbor every 5000 milliseconds and Fast Reroute capability is enabled by specifying the fast-reroute keyword:
Router(config-if)# ip rsvp signalling hello fast-reroute refresh interval 5000In the following example, hello requests are sent to a neighbor every 5000 milliseconds and Fast Reroute capability is enabled by default:
Router(config-if)# ip rsvp signalling hello refresh interval 5000Related Commands
ip rsvp signalling hello refresh misses
To specify how many Resource Reservation Protocol (RSVP) traffic engineering (TE) hello acknowledgments a node can miss in a row before the node considers communication with its neighbor is down, use the ip rsvp signalling hello refresh misses command in interface configuration mode. To return the missed refresh limit to its default value, use the no form of the command.
ip rsvp signalling hello [fast-reroute] refresh misses msg-count
no ip rsvp signalling hello [fast-reroute] refresh misses
Syntax Description
Defaults
The default for the msg-count argument is 4.
Command Modes
Interface configuration
Command History
Usage Guidelines
A hello comprises a hello message, a Hello Request object, and a Hello ACK object. Each request is answered by an acknowledgment. If a link is very congested or a router has a very heavy load, set this number to a value higher than the default value to ensure that hello does not falsely declare that a neighbor is down.
If you issue the ip rsvp signalling hello refresh misses command without the optional fast-reroute keyword, the command applies to Fast Reroute hellos and Fast Reroute capability is enabled by default. This command is provided for backward compatibility; however, we recommend that you use the ip rsvp signalling hello fast-reroute refresh misses command.
Examples
In the following example, if the node does not receive five hello acknowledgments in a row, the node declares that its neighbor is down and Fast Reroute is enabled by specifying the fast-reroute keyword:
Router(config-if)# ip rsvp signalling hello fast-reroute refresh misses 5In the following example, if the node does not receive five hello acknowledgments in a row, the node declares that its neighbor is down and Fast Reroute is enabled by default:
Router(config-if)# ip rsvp signalling hello refresh misses 5Related Commands
Command Descriptionip rsvp signalling hello dscp
Sets the DSCP value in hello messages.
ip rsvp signalling hello
Sets the refresh interval in hello messages.
ip rsvp signalling hello reroute dscp
To set the differentiated services code point (DSCP) value that is in the IP header of a Resource Reservation Protocol (RSVP) traffic engineering (TE) reroute hello (for state timeout) message sent from an interface, use the ip rsvp signalling hello reroute dscp command in interface configuration mode. To set the DSCP to its default value, use the no form of this command.
ip rsvp signalling hello reroute dscp num
no ip rsvp signalling hello reroute dscp
Syntax Description
Defaults
The default DSCP value is 48.
Command Modes
Interface configuration
Command History
Usage Guidelines
If a link is congested, you should set the DSCP to a value higher than 0 to reduce the likelihood that hello messages get dropped.
You configure the DSCP per interface, not per flow.
The DSCP applies to the RSVP hellos created on a specific interface. You can configure each interface independently for DSCP.
Examples
In the following example, hello messages sent from this interface have a DSCP value of 30:
Router(config-if)# ip rsvp signalling hello reroute dscp 30Related Commands
ip rsvp signalling hello reroute refresh interval
To configure the Resource Reservation Protocol (RSVP) Traffic Engineering (TE) reroute hello (for state timeout) refresh interval, use the ip rsvp signalling hello reroute refresh interval command in interface configuration mode. To set the refresh interval to its default value, use the no form of the command.
ip rsvp signalling hello reroute refresh interval interval-value
no ip rsvp signalling hello reroute refresh interval
Syntax Description
interval-value
Frequency, in milliseconds, at which a node sends hello messages to a neighbor. Valid values are from 1000 to 30000 (1 to 30 seconds).
Defaults
10000 milliseconds (10 seconds)
Command Modes
Interface configuration
Command History
Usage Guidelines
You can configure the hello request interval on a per-interface basis. A node periodically generates a hello message containing a Hello Request object for each neighbor whose status is being tracked. The frequency of those hello messages is determined by the hello interval. For some routers, if you set the interval to a value less than the default value, CPU usage may be high.
Examples
In the following example, hello requests are sent to a neighbor every 5000 milliseconds and Fast Reroute capability is enabled by specifying the fast-reroute keyword:
Router(config-if)# ip rsvp signalling hello fast-reroute refresh interval 5000In the following example, hello requests are sent to a neighbor every 5000 milliseconds and Fast Reroute capability is enabled by default:
Router(config-if)# ip rsvp signalling hello refresh interval 5000Related Commands
ip rsvp signalling hello reroute refresh misses
To specify how many Resource Reservation Protocol (RSVP) traffic engineering (TE) reroute hello (for state timeout) acknowledgments (ACKs) a node can miss in a row before the node considers communication with its neighbor is down, use the ip rsvp signalling hello reroute refresh misses command in interface configuration mode. To return the missed refresh limit to its default value, use the no form of the command.
ip rsvp signalling hello reroute refresh misses msg-count
no ip rsvp signalling hello reroute refresh misses
Syntax Description
msg-count
The number of sequential hello acknowledgments (ACKs) that a node can miss before RSVP considers the state expired and tears it down. Valid values are from 4 to 10.
Defaults
The default is 4.
Command Modes
Interface configuration
Command History
Usage Guidelines
A hello comprises a hello message, a Hello Request object, and a Hello ACK object. Each request is answered by an acknowledgment. If a link is very congested or a router has a very heavy load, set this number to a value higher than the default value to ensure that hello does not falsely declare that a neighbor is down.
Examples
In the following example, if the node does not receive five hello acknowledgments in a row, the node declares that its neighbor is down:
Router(config-if)# ip rsvp signalling hello reroute refresh misses 5Related Commands
show ip rsvp hello
To display hello status and statistics for Fast Reroute, reroute (hello state timer), and graceful restart, use the show ip rsvp hello command in user EXEC or privileged EXEC mode.
show ip rsvp hello
Syntax Description
This command has no arguments or keywords.
Command Modes
User EXEC
Privileged EXECCommand History
Examples
The following is sample output from the show ip rsvp hello command:
Router# show ip rsvp helloHello:Fast-Reroute/Reroute: EnabledStatistics: DisabledGracefulRestart: Enabled, mode: fullTable 1 describes the significant fields shown in the display. The fields describe the processes for which hello is enabled or disabled.
Related Commands
Glossary
AS—autonomous system. A collection of networks that share the same routing protocol and that are under the same system administration.
ASBR—autonomous system boundary router. A router that connects and exchanges information between two or more autonomous systems.
backup tunnel—An MPLS traffic engineering tunnel used to protect other (primary) tunnel traffic when a link or node failure occurs.
DSCP—differentiated services code point. Six bits in the IP header, as defined by the IETF. These bits determine the class of service provided to the IP packet.
Fast Reroute—A mechanism for protecting MPLS traffic engineering (TE) LSPs from link and node failure by locally repairing the LSPs at the point of failure, allowing data to continue to flow on them while their headend routers attempt to establish end-to-end LSPs to replace them. FRR locally repairs the protected LSPs by rerouting them over backup tunnels that bypass failed links or nodes.
graceful restart—A process for helping a neighboring route processor restart after a node failure has occurred.
headend—The router that originates and maintains a given LSP. This is the first router in the LSP's path.
IGP—Interior Gateway Protocol. Internet protocol used to exchange routing information within an autonomous system. Examples of common Internet IGPs include IGRP, OSPF, and RIP.
IS-IS—Intermediate System-to-Intermediate System. OSI link-state hierarchical routing protocol whereby Intermediate System (IS) routers exchange routing information based on a single metric to determine network topology.
instance—A mechanism that implements the RSVP hello extensions for a given router interface address and remote IP address. Active hello instances periodically send Hello Request messages, expecting Hello ACK messages in response. If the expected ACK message is not received, the active hello instance declares that the neighbor (remote IP address) is unreachable (that is, it is lost). This can cause LSPs crossing this neighbor to be fast rerouted.
label—A short, fixed-length data identifier that tells switching nodes how to forward data (packets or cells).
LDP—Label Distribution Protocol. The protocol that supports MPLS hop-by-hop forwarding by distributing bindings between labels and network prefixes. The Cisco proprietary version of this protocol is the Tag Distribution Protocol (TDP).
LSP—label-switched path. A configured connection between two routers, in which MPLS is used to carry packets. A path created by the concatenation of one or more label-switched hops, allowing a packet to be forwarded by swapping labels from an MPLS node to another MPLS node.
merge point—The backup tunnel's tail.
MPLS—Multiprotocol Label Switching. A method for forwarding packets (frames) through a network. MPLS enables routers at the edge of a network to apply labels to packets (frames). ATM switches or existing routers in the network core can switch packets according to the labels.
OSPF—Open Shortest Path First. A link-state routing protocol used for routing.
PLR—point of local repair. The headend of the backup tunnel.
RSVP—Resource Reservation Protocol. A protocol that supports the reservation of resources across an IP network. Applications running on IP end systems can use RSVP to indicate to other nodes the nature (bandwidth, jitter, maximum burst, and so on) of the packet streams they want to receive.
state—Information that a router must maintain about each LSP. The information is used for rerouting tunnels.
tailend—The router upon which an LSP is terminated. This is the last router in the LSP's path.
TE—traffic engineering. The techniques and processes used to cause routed traffic to travel through the network on a path other than the one that would have been chosen if standard routing methods had been used.
topology—The physical arrangement of network nodes and media within an enterprise networking structure.
tunnel—Secure communications path between two peers, such as two routers.
Any Internet Protocol (IP) addresses used in this document are not intended to be actual addresses. Any examples, command display output, and figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses in illustrative content is unintentional and coincidental.
© 2004, 2006, 2007 Cisco Systems, Inc. All rights reserved.