BGP Support for IPv6 (Multiprotocol BGP)

ccnp-routing

How multiprotocol extensions let BGP carry IPv6 and other address families over one TCP session, with IPv4 and IPv6 configuration examples.

Published

Jan 22, 2018

BGP v4 was originally intended to carry only IPv4 route information
Multiprotocol BGP (MP-BGP) supports:
- Unicast and Multicast IPv4
- Unicast and Multicast IPv6
- IPv4 and IPv6 route information within customer VRF
- VPNv4 (for use in MPLS L3 VPN), VPNv6, L2VPN, VPLS: not covered in the ROUTE curriculum
Rather than inventing new protocols to carry this information, BGP was modified
with multiprotocol extensions in RFC 2283
MP-BGP uses two new BGP attributes inside the update message. Each of these new attributes will contain one or more AFI (address-family information) that communicates the protocols the prefixes being advertised apply to (IPv4, IPv6, etc)
1. Multiprotocol Reachable NLRI (MP_REACH_NLRI): contains the reachable prefixes for a particular address-family
2. Multiprotocol Unreachable NLRI (MP_UNREACH_NLRI): contains the unreachable or withdrawn prefixes for a particular address-family
Traditionally when R1 and R2 wanted to talk BGP, they would just set up a TCP session and over that TCP session they would have a BGP neighbor peering and over that neighbor peering they would exchange IPv4 unicast routing information.
MP-BGP by default, only has the IPv4 unicast family activated. BGP does not use multicast addresses itself, it will always use a TCP session between two neighbors.
Imagine, we want to exchange routing information for three different things. (IPv4 Unicast, IPv6 Unicast, and IPv4 Multicast) With MP-BGP we have a BGP neighbor session for each particular address family. In this case, we would have three different BGP neighbor sessions, one for each protocol.

Configuration

We want to configure MP-BGP between R5 and R6. First let us convert our old way configuration to the new way.

R5(config)#router bgp 64510
R5(config-router)#address-family ipv4 unicast 
R5(config-router-af)#do show run | s bgp
router bgp 64510
 bgp log-neighbor-changes
 neighbor 2.2.2.2 remote-as 64500
 neighbor 2.2.2.2 ebgp-multihop 2
 neighbor 2.2.2.2 update-source Loopback0
 neighbor 4.4.4.4 remote-as 64510
 neighbor 4.4.4.4 update-source Loopback0
 neighbor 6.6.6.6 remote-as 64520
 neighbor 6.6.6.6 ebgp-multihop 2
 neighbor 6.6.6.6 update-source Loopback0
 !
 address-family ipv4
  network 45.45.45.0 mask 255.255.255.0
  neighbor 2.2.2.2 activate
  neighbor 4.4.4.4 activate
  neighbor 4.4.4.4 next-hop-self
  neighbor 6.6.6.6 activate
 exit-address-family

We see we have got 2 sections:

our underlying BGP configuration (neighbors) - TCP connection

Address-family, we have the specific configuration. Our policies, prefix-lists, route-maps, what we are advertising in, and… Let us convert R6’s BGP configuration now:

R6(config)#router bgp 64520
R6(config-router)#address-family ipv4 unicast 
R6(config-router-af)#do show run | s bgp
router bgp 64520
 bgp log-neighbor-changes
 neighbor 3.3.3.3 remote-as 64500
 neighbor 3.3.3.3 ebgp-multihop 2
 neighbor 3.3.3.3 update-source Loopback0
 neighbor 5.5.5.5 remote-as 64510
 neighbor 5.5.5.5 ebgp-multihop 2
 neighbor 5.5.5.5 update-source Loopback0
 !
 address-family ipv4
  redistribute connected route-map RDtoBGP
  neighbor 3.3.3.3 activate
  neighbor 3.3.3.3 route-map RmASPATH in
  neighbor 5.5.5.5 activate
 exit-address-family

To verify here so far because we configured IPv4 unicast, we can use traditional BGP commands like:

R6#show ip bgp BGP table version is 5, local router ID is 6.6.6.6 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, Origin codes: i - IGP, e - EGP, ? - incomplete RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path

12.12.12.0/24 3.3.3.3 0 64500 64500 64500 64500 i *> 5.5.5.5 0 64510 64500 i

13.13.13.0/24 5.5.5.5 0 64510 64500 i > 3.3.3.3 0 0 64500 i > 45.45.45.0/24 5.5.5.5 0 0 64510 i *> 160.160.160.0/24 0.0.0.0 0 32768 ?

But we cannot verify for other protocols using show ip bgp ..., instead we use show bgp <protocol> for example:

R6#show bgp ipv4 unicast BGP table version is 5, local router ID is 6.6.6.6 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, Origin codes: i - IGP, e - EGP, ? - incomplete RPKI validation codes: V valid, I invalid, N Not found

Network Next Hop Metric LocPrf Weight Path

12.12.12.0/24 3.3.3.3 0 64500 64500 64500 64500 i *> 5.5.5.5 0 64510 64500 i
13.13.13.0/24 5.5.5.5 0 64510 64500 i > 3.3.3.3 0 0 64500 i > 45.45.45.0/24 5.5.5.5 0 0 64510 i *> 160.160.160.0/24 0.0.0.0 0 32768 ?

IPv6 routing over an IPv4 BGP Session

R5 configuration

R5(config)#ipv6 unicast-routing
R5(config)#route-map IPV6-NEXT-HOP
R5(config-route-map)#set ipv6 next-hop 2056::5
R5(config)#router bgp 64510
R5(config-router)#address-family ipv6 
R5(config-router-af)#network 2045::/64       
R5(config-router-af)#neighbor 6.6.6.6 activate
R5(config-router-af)#neighbor 6.6.6.6 route-map IPV6-NEXT-HOP out
R5(config-router-af)#exit

R6 configuration:

R6(config)#route-map IPv6-NEXT-HOP permit
R6(config-route-map)#set ipv6 next-hop 2056::6   
R6(config)#router bgp 64520
R6(config-router)#address-family ipv6
R6(config-router-af)#network 2006::/64
R6(config-router-af)#neighbor 5.5.5.5 activate 
R6(config-router-af)#neighbor 5.5.5.5 route-map IPv6-NEXT-HOP out
R6(config-router-af)#do clear bgp all 64510 soft

Verification

R5#show bgp ipv6 unicast 
BGP table version is 8, local router ID is 5.5.5.5
     Network          Next Hop            Metric LocPrf Weight Path
 *>  2006::/64        2056::6                  0             0 64520 i
 *>  2045::/64        ::                       0         32768 i