If you are sharing IPv6 route information, you need to send it to a router that's capable of that! So the config, as asked for, will be helpful...
But if you send to a router with no IPv6 knowledge I would expect the necessary information (like next hop) to be removed since it's unreachable!
With iBGP, you can have anyone in your network peer as long as you have reachability (e.g. not directly connected), so you may be able to cut out a router in the middle which isn't confiugred for IPv6.
thanks many for your reply. When I enabled ipv6 capability on both the DUTs, ipv4 neighbor-ship did not go down. But, on DUT2 alone, I added ipv6 nexthop as one of its own interfaces. My intention is to exchange DUT2 side ipv6 prefixes to DUT1. But, the moment I added ipv6 next hop *only on DUT2* ipv4 iBGP neighbor-ship is going down. Is this because of the UPDATE message from DUT1 has NULL for ipv6 prefixes ? If that is the case, ipv6 prefixes exchange should fail, but not ipv4 neighbor-ship, right ? And my 2nd doubt was, does the BGP UPDATE message can impact BGP connection ? I could not find any such info from RFC 2545 Section 3, and also from RFC 4271 Section 4.3 which talks about UPDATE message.