Hi Nobo,
thank you for your thoughtful and interesting, as always, comments.
I've realized, after the session, that encapsulation of BFD Echo over LSP or PW
MUST be different from what defined in RFC 5880. I think it must follow the
same principle as set in RFC 5884 for Async BFD mode.
And I agree that PW, unlike LSP (at least most LSP constructs), is a
bi-directional construct. Thus, as I think of it, operators more interested in
verifying data plane availability in both directions. If we propose two-way
single-ended mechanism to check data path of the particular PW, then, I
imagine, the return path MUST be in-band, not over IP path. I think that we
need to note that in our discussion of S-BFD or BFD Echo over VCCV as a
requirement. Then we can see whether extending BFD Echo to MPLS LSP and PW or
using S-BFD bring better solution, particularly since we already have ICMP and
LSP Ping over VCCV defined.
Regards,
Greg
From: Nobo Akiya [mailto:[email protected]]
Sent: Monday, March 23, 2015 6:19 PM
To: Gregory Mirsky; [email protected]
Subject: RE: BFD Echo format
Hi Greg,
I believe this comment was in context of S-BFD for VCCV.
>From what I understand, the scenario which S-BFD for VCCV is looked into is
>the case where one end of the PW has very constrained resources. Using the
>classical BFD will require such devices to maintain a session object per PW,
>as opposed to S-BFD which only requires one reflector session.
Your comment about why not send BFD echo packets over the PW? Sending a probe
(BFD echo) with IP destination having the sender address, across multiple
physical hops, always has the danger of the probe packet still coming back to
the sender despite issues. Yes this is more likely on LSPs like LDP, RSVP (and
less likely on PW) but it is possible that PW label gets exposed "somewhere"
and that label value happens to match a different LSP, picking up traversal to
a different node.
Then there's the desire for return packets to come back on the reverse
direction of the forward PW. Whether we go with S-BFD for VCCV or BFD echo,
this (i.e., reflector bouncing back packets on the reverse PW) is a change that
needs to be made/standardized.
So to me, S-BFD for VCCV makes sense.
Thanks!
-Nobo
From: Rtg-bfd
[mailto:[email protected]]<mailto:[mailto:[email protected]]> On
Behalf Of Gregory Mirsky
Sent: March-23-15 1:54 PM
To: [email protected]<mailto:[email protected]>
Subject: BFD Echo format
Dear All,
I stand corrected, BFD Echo format is not defined in the RFC 5880 but there
requirement suggesting that BFD Discriminator MAY be used to demux Echo replies:
The payload of a BFD Echo packet is a local matter, since only the
sending system ever processes the content. The only requirement is
that sufficient information is included to demultiplex the received
packet to the correct BFD session after it is looped back to the
sender. The contents are otherwise outside the scope of this
specification.
Regards,
Greg
