Re: [bess] A question about the draft-wang-bess-sbfd-discriminator

[Greg Mirsky <[e-mail]>]

Hi Reshad,
I agree with you that if in all the deployment scenarios there's always
only one node in a pair of nodes that needs to be aware of the path
continuity to the remote system, then S-BFD has an advantage compared to
"classic" RFC 5880-style BFD. I think that the use case presented in the
document is not generic. In the more general case, as I imagine, PEs
connected to CE1 and CE2 would benefit from monitoring the undelay network
continuity between them. Hence, my suggestion to use RFC 5880-style BFD
rather than S-BFD.

Regards,
Greg

On Mon, Mar 14, 2022 at 7:36 PM Reshad Rahman <[e-mail]> wrote:

> Hi Greg, authors,
>
>
> Greg, is your point is that instead of having a pair of S-BFD sessions
> between 2 PEs, we can have 1 (traditional) BFD session between 2 PEs? In
> general I agree that S-BFD is better suited when only 1 side needs to
> perform continuity tests.
>
> Authors, in section 3.1 3rd paragraph, last sentence, I'm not sure I fully
> understand. Instead of having 2 S-BFD sessions on PE3 (as initiator) to PE1
> and PE2 (the responders), how are you merging this into 1 single session?
>
> Also, I think the document would be clearer if the terms initiator and
> responder (as per RFC7880) are used in the document.
>
> Regards,
> Reshad.
>
>
> On Monday, March 14, 2022, 12:44:55 PM EDT, Greg Mirsky <
> [e-mail]> wrote:
>
>
> Hi Haibo and the Authors,
> thank you for updating the draft. I've read the new version and have a
> question about the use case presented in the document. There are three PEs
> with two of them providing redundant access to a CE. It appears that a more
> general case would be if both CEs use redundant connections to the EVPN.
> Asume, PE4 is added and connected to CE2. In that case, it seems reasonable
> that each PE is monitoring remote PEs, i.e., PE1 monitors PE3 and PE4, PE2
> - PE3 and PE4, PE3 - PE1 and PE2, and PE4 - PE1 and PE2. So, now there are
> pairs of S-BFD sessions between PEs connected to CE1 and CE2 respectively.
> That seems like too many sessions and that number can be reduced if one
> uses BFD instead of S-BFD. Would you agree? To simplify operations, it
> might be helpful to use the technique described in
> draft-ietf-bfd-unsolicited
> <https://datatracker.ietf.org/doc/html/draft-ietf-bfd-unsolicited-09>. In
> the recent discussion of the draft on the BFD WG ML, the authors noted that
> they are working on extending the scope to include the multi-hop BFD.
> Greatly appreciate your thoughts about the number of S-BFD sessions.
>
> Regards,
> Greg
>