what does mean the command under bgp protocol no ipv4 unicast
if no write no ipv4-unicast what’s happen ?
If I’m not mistaken you mean the
no bgp default ipv4-unicast command.
bgp default ipv4-unicast command will set the IPv4 unicast address family as the default for BGP peering session establishment. This is actually the default behaviour for each BGP session that is configured with the
neighbor remote-as command. By issuing the
no version of the command, you are essentially enabling multi protocol GPB mode, where multiple address families can be negotiated during the BGP session setup.
Now from what I read, it may no longer be necessary in newer versions of IOS as the default behaviour of BGP has been changed to be multi protocol, but you will have to check that on a per version basis.
I hope this has been helpful!