vpnv4, ipv4 and next-hop-self

MATTHIAS SCHAERER · ‎07-30-2010

In a back-to-back VPN connection (prefixes are transferred as ipv4 prefixes in an eBGP session) we observe that the ASBR imports prefixes into vpnv4 with next-hop-self. For ipv4 next-hop-self is not automatically set. Is there any explanation, documentation or even standard for this different treatment of the prefixes?

Thanks for any hint.

mat

Giuseppe Larosa · ‎07-30-2010

Hello Matthias,

in address family vpnv4 the next-hop is changed automatically, because it needs to be an address in the global routing table and so the eBGP next-hop learned in the eBGP session in VRF cannot be reused.

This is needed in order to have a working forwarding plane

This does not happen in af ipv4 because the original eBGP next-hop can be retained being part of global routing table on ASBR/PE node, in this case setting next-hop self may solve problems of installation of BGP routes in downstream iBGP peers as they could not know how to reach theoriginal BGP next-hop.

Hope to help

Giuseppe