IP Addressing: DHCP Configuration Guide, Cisco IOS XE Gibraltar 16.11.x
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A Dynamic Host Configuration Protocol for IPv6 (DHCPv6) relay agent, which may reside on the client's link, is used to relay
messages between the client and the server.
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Information About IPv6 Access Services: DHCPv6 Relay Agent
DHCPv6 Relay Agent
A DHCPv6 relay agent,
which may reside on the client’s link, is used to relay messages between the
client and the server. The DHCPv6 relay agent operation is transparent to the
client. A DHCPv6 client locates a DHCPv6 server using a reserved, link-scoped
multicast address. For direct communication between the DHCPv6 client and the
DHCPv6 server, both of them must be attached to the same link. However, in some
situations where ease of management, economy, or scalability is a concern, it
is desirable to allow a DHCPv6 client to send a message to a DHCPv6 server that
is not connected to the same link. IPv6 enable is required for IPv6 DHCP relay,
although IPv6 address is configured.
DHCPv6 Relay Agent
Notification for Prefix Delegation
The DHCPv6 relay
agent notification for prefix delegation allows the device working as a DHCPv6
relay agent to find prefix delegation options by reviewing the contents of a
DHCPv6 RELAY-REPLY packet that is relayed by the relay agent to the client.
When a prefix delegation option is found by the relay agent, the relay agent
extracts the information about the prefix that is being delegated and inserts
an IPv6 static route matching the prefix delegation information onto the relay
agent. Future packets destined to that prefix via relay will be forwarded based
on the information contained in the prefix delegation. The IPv6 static route is
then left in the routing table until the prefix delegation lease time expires
or the relay agent receives a release packet from the client releasing the
prefix delegation.
No user
configuration is required for this feature. Static route management is done
automatically by the relay agent.
IPv6 routes are
added when the relay agent relays a RELAY-REPLY packet, and IPv6 routes are
deleted when the prefix delegation lease time expires or the relay agent
receives a release message. An IPv6 static route in the routing table of the
relay agent can be updated when the prefix delegation lease time is extended.
The DHCP—DHCPv6
Relay Agent Notification for Prefix Delegation feature leaves a static IPv6
route on the routing table of the relay agent. The registered IPv6 address
allows unicast reverse packet forwarding (uRPF) to work by allowing the device
doing the reverse lookup to confirm that the IPv6 address on the relay agent is
not malformed or spoofed. The static route that remains in the routing table of
the relay agent can be redistributed to other routing protocols to advertise
the subnets to other nodes. Static routes will be removed when a DHCP_DECLINE
message is sent by the client.
DHCPv6 Relay Options:
Remote-ID for Gigabit Ethernet and Fast Ethernet Interfaces
The DHCPv6 Ethernet
Remote ID Option feature adds the remote identification (remote-ID) option to
relayed (RELAY-FORWARD) DHCPv6 packets.
The remote-ID
option provides information to the DHCPv6 server, which includes port
information, the system’s DUID, and the VLAN ID. This information can be used
to uniquely identify both the relay and the port on the relay through which the
client packet arrived. The DHCPv6 server uses this information to select
parameters specific to a particular user, host, or subscriber modem.
The addition of the
remote-ID option to the RELAY-FORWARD packet occurs automatically and no user
configuration is necessary.
The DHCPv6 server
does not need to echo the remote-ID option in the RELAY-REPLY packet. The
Internet Assigned Numbers Authority (IANA) has assigned the DHCPv6 option code
37 for the relay agent remote-ID option.
If the remote-ID
option is included in the RELAY-REPLY packet, the option is removed from the
packet before it is relayed to the client.
DHCPv6 Relay Options: Reload
Persistent Interface ID
The DHCPv6
Relay—Reload Persistent Interface ID Option feature makes the interface ID
option persistent. The interface ID is used by relay agents to decide which
interface should be used to forward a RELAY-REPLY packet. A persistent
interface-ID option will not change if the device acting as a relay agent goes
offline during a reload or a power outage. When the device acting as a relay
agent returns online, it is possible that changes to the internal interface
index of the relay agent may have occurred in certain scenarios (such as, when
the relay agent reboots and the number of interfaces in the interface index
changes, or when the relay agents boot up and has more virtual interfaces than
it did before the reboot). This feature prevents such scenarios from causing
any problems.
This feature
changes the DHCPv6 interface-ID option to be expressed as the short form of the
interface name. The interface name as the DHCPv6 interface ID helps avoid
potential problems that could arise due to physical or logical interfaces
changing on the relay agent after a reload.
DHCPv6 Relay Chaining
DHCPv6 messages can
be relayed through multiple relay agents. This configuration is called
relay
chaining. A relay chaining configuration can be supported only when each
relay agent adds information to DHCPv6 messages before relaying them. The
information helps in relaying the DHCPv6 reply back to the DHCPv6 client
through the same path.
The delegated IPv6 prefix must be routable in order to be useful.
The actual DHCPv6 Prefix Delegation (PD) client may not be permitted to inject
routes into the delegating network. In service provider (SP) networks, for
example, an edge device typically acts as a DHCPv6 relay agent, and this edge
device often has the responsibility to maintain routes within the SP network
for clients’ PD bindings. In the event that DHCPv6 requests and responses are
relayed through a chain of DHCPv6 relays, there may be a need to introduce
appropriate routes (particularly with DHCPv6 PD) in the Forwarding Information
Base (FIB) so that routing is handled transparently.
DHCPv6 Relay Agent Notification for Prefix Delegation
The DHCPv6 relay agent notification for prefix delegation allows the device working as a DHCPv6 relay agent to find prefix
delegation options by reviewing the contents of a DHCPv6 RELAY-REPLY packet that is relayed by the relay agent to the client.
When a prefix delegation option is found by the relay agent, the relay agent extracts the information about the prefix that
is being delegated and inserts an IPv6 static route matching the prefix delegation information onto the relay agent. Future
packets destined to that prefix via relay will be forwarded based on the information contained in the prefix delegation. The
IPv6 static route is then left in the routing table until the prefix delegation lease time expires or the relay agent receives
a release packet from the client releasing the prefix delegation.
No user configuration is required for this feature. Static route management is done automatically by the relay agent.
IPv6 routes are added when the relay agent relays a RELAY-REPLY packet, and IPv6 routes are deleted when the prefix delegation
lease time expires or the relay agent receives a release message. An IPv6 static route in the routing table of the relay agent
can be updated when the prefix delegation lease time is extended.
The DHCP—DHCPv6 Relay Agent Notification for Prefix Delegation feature leaves a static IPv6 route on the routing table of
the relay agent. The registered IPv6 address allows unicast reverse packet forwarding (uRPF) to work by allowing the device
doing the reverse lookup to confirm that the IPv6 address on the relay agent is not malformed or spoofed. The static route
that remains in the routing table of the relay agent can be redistributed to other routing protocols to advertise the subnets
to other nodes. Static routes will be removed when a DHCP_DECLINE message is sent by the client.
DHCPv6 Relay Options: Remote ID for Ethernet Interfaces
This feature adds the remote identification (remote-ID) option to relayed (RELAY-FORWARD) DHCPv6 packets.
The remote-ID option provides information to the DHCPv6 server, including port information, the system’s DUID, and the VLAN
ID. Collectively, this information can be used to uniquely identify both the relay and the port on the relay through which
the client’s packet arrived. The DHCPv6 server uses this information to select parameters specific to a particular user, host,
or subscriber modem. This feature works only for Ethernet interfaces at this time.
This feature introduces no user configuration. Because the addition of the remote-ID option to the RELAY-FORWARD packet occurs
automatically, no user configuration is necessary.
The DHCPv6 server does not need to echo the remote-ID option in the RELAY-REPLY packet. Internet Assigned Numbers Authority
(IANA) has assigned the DHCPv6 option code 37 for the relay agent remote-ID option.
If the remote-ID option is included in the RELAY-REPLY packet, the option is stripped out of the packet before the packet
is relayed to the client.
DHCPv6 Relay Options: Reload Persistent Interface ID Option
This feature makes the interface-ID option, which is used by relay agents to decide which interface should be used when forwarding
a RELAY-REPLY packet, persistent. A persistent interface-ID option will not change if the router acting as a relay agent goes
offline (such as during a reload or a power outage). When the router acting as a relay agent returns online, it is possible
that changes to the internal interface index of the relay agent may have occurred in certain scenarios (such as cases where
the relay agent reboots and has a change in the number of interfaces in the interface index, or the relay agents boots up
and has more virtual interfaces than it did before the reboot). This feature prevents this scenario from causing any problems.
This feature changes the DHCPv6 interface-ID option to be expressed as simply the short form of the interface name. This
syntax helps avoid potential problems that could arise due to physical or logical interfaces changing on the relay agent after
a reload.
DHCPv6 Relay Chaining
This feature makes the interface-ID option, which is used by relay agents to decide which interface should be used when forwarding
a RELAY-REPLY packet, persistent. A persistent interface-ID option will not change if the router acting as a relay agent goes
offline (such as during a reload or a power outage). When the router acting as a relay agent returns online, it is possible
that changes to the internal interface index of the relay agent may have occurred in certain scenarios (such as cases where
the relay agent reboots and has a change in the number of interfaces in the interface index, or the relay agents boots up
and has more virtual interfaces than it did before the reboot). This feature prevents this scenario from causing any problems.
This feature changes the DHCPv6 interface-ID option to be expressed as simply the short form of the interface name. This
syntax helps avoid potential problems that could arise due to physical or logical interfaces changing on the relay agent after
a reload.
How to Configure IPv6 Access Services: DHCPv6 Relay Agent
Specifies a
destination address to which client packets are forwarded and enables the
DHCPv6 relay service on the interface.
Step 6
end
Example:
Device(config-if)# end
Returns to
privileged EXEC mode.
Configuration Examples for IPv6 Access Services: DHCPv6 Relay Agent
Example: Configuring the DHCPv6 Relay Agent
Device# show ipv6 dhcp interface
Ethernet1/0 is in relay mode
Relay destinations:
3FFB:C00:C18:6:A8BB:CCFF:FE03:2701
Serial3/0 is in relay mode
Relay destinations:
3FFB:C00:C18:6:A8BB:CCFF:FE03:2600
FE80::A8BB:CCFF:FE03:2801 on Serial3/0
FF05::1:3
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Feature Information for
IPv6 Access Services: DHCPv6 Relay Agent
The following table provides release information about the feature or features described in this module. This table lists
only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise,
subsequent releases of that software release train also support that feature.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco
Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 1. Feature Information for
IPv6 Access Services: DHCPv6 Relay Agent
Feature Name
Releases
Feature
Information
IPv6 Access
Services: DHCPv6 Relay Agent
Cisco IOS XE Release 3.9S
A DHCP relay
agent, which may reside on the client’s link, is used to relay messages between
the client and server.
The
following commands were introduced or modified:
ipv6 dhcp relay
destination ,
show ipv6 dhcp
interface .
DHCPv6 Relay
Agent Notification for Prefix Delegation
Cisco IOS XE Release 3.13S
In Cisco IOS XE Release 3.13S, support was added for the Cisco
ASR 903 Router.
DHCPv6 relay
agent notification for prefix delegation allows the device working as a DHCPv6
relay agent to find prefix delegation options by reviewing the contents of a
DHCPv6 packet that is being relayed by the relay agent to the client.
DHCPv6
Relay: Reload Persistent Interface ID Option
Cisco IOS XE Release 3.9S
This feature
makes the interface-ID option, which is used by relay agents to decide which
interface should be used when forwarding a RELAY-REPLY packet, persistent.
DHCPv6—Relay
chaining for Prefix Delegation
Cisco IOS XE Release 3.9S
This feature
enables DHCPv6 messages to be relayed through multiple relay agents.
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