BGP Capabilities Advertisment

While setting up an IPv6 lab i have encounter a strange output from one of the routers, although the BGP peer has been setup  and they have exchange prefixes, R4 show ip bgp summary output shows the following:

Note the (NoNeg) under the state/PfxRcd section.

Looking on R1 configuration i have noticed that no neighbor 2001::4 active has been configured under IPv4 address family and that's despite the fact that I'm not using an IPv4 at all.

Doing some packet capture pointed to the reason of BGP capabilities advertisement, while the neighbor is not activate, in IPv4 and IPv6, he is not advertising his capabilities to his peer neighbor:

changing the neighbor to activate has solved this issue:

note that this happens only with IPv4 while IPv6 is running normal: