BGP is a typical CCNP/CCIP topic, as is IPv6. But a combination of the two is rarely mentioned. Yet, just as with IPv4, BGP is mandatory for internet access. For IPv6, MultiProtocol BGP or MP-BGP is used.

MP-BGP

In the above sample network, both routers are part of a different AS. They have loopbacks configured with a subnet that has to be advertised by BGP. The link between the two is also IPv6. To configure MP-BGP you’ll need a reasonably up to date IOS: I’m using a 12.4. The config of the left router:

R1(config)#ipv6 unicast-routing
R1(config)#int lo0
R1(config-if)#ipv6 address 2001:0:0:10::1/64
R1(config-if)#exit
R1(config)#int f0/0
R1(config-if)#ipv6 address 2001:0:1:1::1/64
R1(config-if)#no shut
R1(config-if)#exit
R1(config)#router bgp 65001
R1(config-router)#no bgp default ipv4-unicast
R1(config-router)#bgp router-id 1.1.1.1
R1(config-router)#neighbor 2001:0:1:1::2 remote-as 65002
R1(config-router)#address-family ipv6
R1(config-router-af)#neighbor 2001:0:1:1::2 activate
R1(config-router-af)#network 2001:0:0:10::/64
R1(config-router-af)#exit-address-family

Some details here. ‘ipv6 unicast-routing’ is obviously required to make IPv6 routing possible. The interfaces are configured with the appropriate addresses and BGP for AS 65001 is set up. ‘no bgp default ipv4-unicast’ is the first important command here: it changes BGP to support multiple protocols. ‘address-family ipv6’ is the second important command: it defines the IPv6 parameters. Just like with standard BGP, a ‘network’ command defines the network(s) to advertise. And just like standard BGP, the network has to be present in the local routing table or no advertisement will be made.

Note that I’m advertising a /64 subnet here. While this works, in practice most ISPs will not accept a prefix more specific than a /48. Also, for once the ‘exit’ command is different, though typing ‘exit’ will work just the same. Oh, and the ‘router-id’ command is because no IPv4 address has been defined, which normally determines the router-id.

The config of the right router:

R2(config)#ipv6 unicast-routing
R2(config)#int f0/0
R2(config-if)#ipv6 addr 2001:0:1:1::2/64
R2(config-if)#no shut
R2(config-if)#int lo0
R2(config-if)#ipv6 address 2001:0:0:20::1/64
R2(config-if)#exit
R2(config)#router bgp 65002
R2(config-router)#no bgp default ipv4-unicast
R2(config-router)#bgp router-id 2.2.2.2
R2(config-router)#address-family ipv6
R2(config-router-af)#neighbor 2001:0:1:1::1 activate
% Specify remote-as or peer-group commands first
R2(config-router-af)#neighbor 2001:0:1:1::1 remote-as 65001
R2(config-router-af)#neighbor 2001:0:1:1::1 activate
*Mar  1 00:09:49.171: %BGP-5-ADJCHANGE: neighbor 2001:0:1:1::1 Up
R2(config-router-af)#network 2001:0:0:20::/64
R2(config-router-af)#end

A similar configuration. This time I’ve set the ‘neighbor remote-as’ command inside the ‘address family ipv6’ context. This does not seem to matter, as long as it is defined before the activation command. Just like BGP, MP-BGP uses TCP port 179 for the connection, which you can see with the following command:

R2#show tcp brief
TCB       Local Address           Foreign Address        (state)
64F460B8  2001:0:1:1::2.179       2001:0:1:1::1.26321    ESTAB

It also show that the left router (R1) initiated the connection to R2 on port 179. The result is visible with ‘show ipv6 route’:

B   2001:0:0:10::/64 [20/0]
via FE80::C000:3FF:FEA4:0, FastEthernet0/0

MP-BGP works and networks are propagated.

Interestingly, the IOS allows you to define IPv4 MP-BGP peers for IPv6 networks, accepting all commands. It even tries to set up a TCP connection, but this connection times out, looping forever and never establishing completely. I’m not sure why this is, as I had expected the TCP session to form but no information being exchanged because of missing next-hop IPv6 addresses. It seems IOS is a bit buggy on this part.

I used this information on the Cisco website as part of this example.

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