Multiprotocol BGP (MP-BGP) Configuration

Lessons Discussion
36

Hi Brandon,

Both options are possible. This sentence is confusing though:

Both routers will now advertise their IPv6 address as the next hop for all prefixes that are advertised.

This isn’t correct since we fix the issue inbound, the routers still have no next hop to advertise. I just changed this sentence.

Let me explain this in detail. We can see what R1 advertises to R2:

R1#show ip bgp ipv6 unicast neighbors 192.168.12.2 advertised-routes 
BGP table version is 4, local router ID is 192.168.12.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
              t secondary path, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>   2001:DB8::1/128  ::                       0         32768 i

Total number of prefixes 1

When R2 receives this prefix, there is no valid next hop, so it shows up like this:

*  2001:DB8::1/128  ::FFFF:192.168.12.1

To fix this, you have two options:

  • Fix it inbound on R1 with an inbound route-map like I did.
  • Fix it outbound on R2 with an outbound route-map.

This also applies the other way around for prefixes that R2 advertises to R1.

Both options work. Here’s an example of an outbound route-map:

R1(config)#route-map IPV6_MY_NEXT_HOP permit 10
R1(config-route-map)#set ipv6 next-hop 2001:DB8:0:12::1

R1(config)#router bgp 1
R1(config-router)#address-family ipv6
R1(config-router-af)#no neighbor 192.168.12.2 route-map IPV6_NEXT_HOP in
R1(config-router-af)#neighbor 192.168.12.2 route-map IPV6_MY_NEXT_HOP out

Delete the inbound route-map on R2:

R2(config)#router bgp 2
R2(config-router)#address-family ipv6
R2(config-router-af)#no neighbor 192.168.12.1 route-map IPV6_NEXT_HOP in

Reset BGP to speed things up:

R1#clear ip bgp *

Check R2:

R2#show ip bgp ipv6 unicast
BGP table version is 3, local router ID is 192.168.12.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal, 
              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter, 
              x best-external, a additional-path, c RIB-compressed, 
              t secondary path, 
Origin codes: i - IGP, e - EGP, ? - incomplete
RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf Weight Path
 *>   2001:DB8::1/128  2001:DB8:0:12::1
                                                0             0 1 i
 *>   2001:DB8::2/128  ::                       0         32768 i

R2 has the correct next hop but this time we fixed it from the source (R1).

Both options work, I agree it might be “cleaner” to fix it outbound on R1 but both are valid options.

I hope this helps!

Rene

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