Last Call Review of draft-ietf-nvo3-bfd-geneve-10
review-ietf-nvo3-bfd-geneve-10-tsvart-lc-westerlund-2023-07-03-00

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I have reviewed BFD for Geneve (draft-ietf-nvo3-bfd-geneve-10) and have one
significant point on this protocol. So when BFD was published after quite some
discussion about the lack of an actual congestion control mechanism in BFD in
RFC 5880 there was agreement on the following that was included in Section 7 of
RFC 5880:

   When BFD is used across multiple hops, a congestion control mechanism
   MUST be implemented, and when congestion is detected, the BFD
   implementation MUST reduce the amount of traffic it generates.  The
   exact mechanism used is outside the scope of this specification, and
   the requirements of this mechanism may differ depending on how BFD is
   deployed, and how it interacts with other parts of the system (for
   example, exponential backoff may not be appropriate in cases where
   routing protocols are interacting closely with BFD).

As this usage of BFD although is point to point inside the tunnel, the fact
that it is a tunnel and can bridge both multisegment L2 and especially IP
networks means that this document in my view need to define how it fulfills the
above requirements when using BFD.

I do note the security consideration do note that overload is a factor due to
multiple path sharing tunnel establishments. So there are apparently risks from
two types of overlad situations here. First that multiple tunnles between
endpoints are established. Secondly, that there are congestion due to network
cross traffic on the paths the tunnels share.

So I think there are two paths forward. Either restrict the applicability of
this usage to paths where it is known to have provisioned capacity for the BFD,
as noted as required in RFC 5881 applicability statement. The alternative is to
extend BFD to actually have a real congestion control. Something I think would
have benefit all considering how wide spread use there is of BFD over various
overlay networks that really are ignoring this potential issue.

To conclude I am of the oppinion that this document should not be approved for
publication until this issue of congestion control is handled one way of
another.