Here are the pros and cons of single BGP transport (one transport using IPv4 for both IPv4 and IPv6 routing information) versus dual transport (IPv4 and IPv6 routing information have individual neighbors of the same protocol).
With a single IPv4 TCP session:
- Reduction in the number of neighbors reduces complexity and makes troubleshooting easier
- To properly route IPv6, you will likely have to specify the IPv6 next-hop attribute with a route-map, as IPv6 cannot route with an IPv4 next-hop address.
With separate TCP sessions:
- There is complete independence between IPv4 and IPv6
- Duplicate configurations in some circumstances means more work
- No need to set the IPv6 next-hop attribute with a route-map
- IPv6 neighbors are not seen in the show ip bgp summary output; you must instead issue the command show bgp ipv6 unicast summary
Stuck-in-Active: Journal of an IT-Network Administrator 