Greg, > On Aug 11, 2017, at 2:12 PM, Greg Mirsky <gregimir...@gmail.com> wrote: > > Re-sending to the corrected list (apologies for duplicates). > > Dear All, > I suggest to reject this proposal. The current text is clear and the > mechanics of bootstrapping BFD session over MPLS LSP is well understood - > remote peer MUST start sending BFD control packets first and BFD peer MAY > send Echo Reply with its Local Discriminator as value in BFD Discriminator > TLV. >
This seems to repeat the text in 5884 without explaining why you feel a particular interpretation is the correct technical one. The text you include: “MAY send Echo Reply with its Local Discriminator as value in BFD Discriminator TLV” suffers from the ambiguity that this Errata is trying to clarify. Which one is it? * (MAY send Echo Reply with its Local Disc) * (MAY send Echo Reply), with its Local Disc. The actual text is: The egress LSR MAY respond with an LSP Ping Echo ! reply message that carries the local discriminator assigned by it for the BFD session. And NOT: The egress LSR MAY respond with an LSP Ping Echo ! reply message, which carries the local discriminator assigned by it for the BFD session. Based on restrictive versus non-restrictive clause, I feel it is correct to accept the errata. And by the way, RFC 5884 is not say what happens if the LSP Ping Reply has a different discriminator value! Thanks, Carlos. > Regards, > Greg > > > On Fri, Aug 11, 2017 at 10:39 AM, Jeffrey Haas <jh...@pfrc.org> wrote: > [Note that I have adjusted the addresses in the headers to try to catch the > RFC authors' current accounts.] > > > The 5884 interop issue keeps bubbling up. Balaji submitted an errata, which > provides us with a good place to start technical discussion. > > Please note I also spent some time off-list discussing this errata with > Balaji. > > > On Thu, Aug 10, 2017 at 10:35:50PM -0700, RFC Errata System wrote: > > Section: 6 > > > > Original Text > > ------------- > > The egress LSR MAY respond with an LSP Ping Echo > > reply message that carries the local discriminator assigned by it for > > the BFD session. > > > > Corrected Text > > -------------- > > The egress LSR MUST respond with an LSP Ping Echo reply message that > > MAY carry the local discriminator assigned by it for the BFD session. > > > > > > Notes > > ----- > > It is not clear from the original text which of the following is optional: > > - The egress MUST send a reply, but the discriminator in the reply is > > optional > > - The reply itself is optional > > > > Technically, the reply cannot be optional, because the egress needs to > > report LSP-Ping verification status to the ingress. > > > > The proposed text recommends to include BFD discriminator in the reply. > > This was the intent of the original text. > > My opinion follows: > > In section 6 - > > : On receipt of the LSP Ping Echo request message, the egress LSR MUST > : send a BFD Control packet to the ingress LSR, if the validation of > : the FEC in the LSP Ping Echo request message succeeds. This BFD > : Control packet MUST set the Your Discriminator field to the > : discriminator received from the ingress LSR in the LSP Ping Echo > : request message. The egress LSR MAY respond with an LSP Ping Echo > : reply message that carries the local discriminator assigned by it for > : the BFD session. The local discriminator assigned by the egress LSR > : MUST be used as the My Discriminator field in the BFD session packets > : sent by the egress LSR. > > In the text above, I consider it quite clear that the receipt of the BFD > packet contains sufficient state to bring up the BFD session. The receipt > of the same Discriminator in the LSP Ping Echo Reply is optional. > > This makes sense partially because the reply may be dropped and we want the > BFD session to come up as fast as possible. > > The point of contention appears to be what to do if we *never* get such > replies. It's worth pointing out additional text in RFC 5884, section 3.2. > > : Hence, BFD is used in conjunction with LSP Ping for MPLS LSP fault > : detection: > : > : i) LSP Ping is used for bootstrapping the BFD session as described > : later in this document. > : > : ii) BFD is used to exchange fault detection (i.e., BFD session) > : packets at the required detection interval. > : > : iii) LSP Ping is used to periodically verify the control plane > : against the data plane by ensuring that the LSP is mapped to > : the same FEC, at the egress, as the ingress. > > iii above reminds us that the LSP may be torn down because LSP Ping fails. > Thus, it seems problematic that we do not get a reply ever. > > However, with the BFD session in the Up state, we have information proving > that the LSP is up. Thus we have contradictory intent. > > --- > > My opinion is that the MAY in the RFC 5884 procedures is intended to have > the BFD session come up by the most expedient means. I do not believe the > likely intent was to say "don't send Echo Reply". Among other things, that > seems contrary to the intent of the general LSP Ping procedures. > > Having given my personal observations, we now get to the business of the > Working Group: Debating intent and related text. > > -- Jeff > > — Carlos Pignataro, car...@cisco.com “Sometimes I use big words that I do not fully understand, to make myself sound more photosynthesis."