Les, The obvious issue is scale. Since you need a full mesh you are talking > about N**2 behavior – so it doesn’t take many nodes to require thousands of > BFD sessions. >
That does sound scary doesn't it ? 1000s is a rather big number ... :) Well good news is that we have recently finished work and moved to IESG with unsolicited BFD proposal: https://datatracker.ietf.org/doc/html/draft-ietf-bfd-unsolicited-09 That means that you can use BFD probes with zero configured session(s) yet get full benefit of remote liveness discovery. Just imagine when BGP registered with the RIB request to track given the next hop you trigger such BFD probes at requested frequency. Zero change to control plane nor data plane. Yet full benefit. And while we are at this point let's observe that most if not all real PEs can respond to BFD in line cards and the amount of such traffic would be completely negligible when considering forwarding performance of today's production PEs both in terms of PPS or LC throughput. Cheers, Robert. >
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