On 09/05/11 05:47, Yaakov Stein wrote: > > Stewart > > I will answer your specific questions below. > > I have no specific objection to the new text that you proposed on the > PWE3 list : > > In MPLS-TP, the GAL MUST be used with packets on a G-ACh on > LSPs, Concatenated Segments of LSPs, and with Sections, and > MAY be used with PWs. The presence of a GAL indicates that > an ACH immediately follows the MPLS label stack. > > as it has become so generic (does not explain where the GAL is placed) > as to be noncontroversial. > > However, please be aware that this simply postpones the true discussion. > This is correct. This document was not meant to have a discussion about OAM. Thanks Yaakov.
Luca > I would still like the wording > > According to the MPLS-TP requirement document [RFC5654], it is > > necessary that MPLS-TP mechanisms and capabilities be able to > > interoperate with the existing IETF MPLS [RFC3031] and IETF PWE3 > > [RFC3985] architectures appropriate. > > to be removed, as I believe that it does not correctly describe the > purpose of this draft. > > It should be replaced with the text that appears further on > > The inconsistency between the usage of the GAL with MPLS PWs and > > MPLS-TP PWs may cause unnecessary implementation differences and is > > in disagreement with the MPLS-TP requirements. > > Please see a few more remarks interleaved below. > > Y(J)S > > > -------- Original Message -------- > > *Subject: * > > > > Re: FW: [PWE3] Last Call: (Using the Generic Associated Channel Label > for Pseudowire in MPLS-TP) to Proposed Standard > > *Date: * > > > > Thu, 01 Sep 2011 16:40:16 +0100 > > *From: * > > > > Stewart Bryant <[email protected]> <mailto:[email protected]> > > *Reply-To: * > > > > [email protected] <mailto:[email protected]> > > *To: * > > > > Yaakov Stein <[email protected]> <mailto:[email protected]> > > *CC: * > > > > [email protected] <mailto:[email protected]> <[email protected]> > <mailto:[email protected]> > > … > > However, you did not address my other final comment that a PW that > starts in an MPLS-TP domain, > > can easily leak into a non-TP domain. > > What does one do then ? > > That is a general issue rather than a TP issue. > When you get to the PW label and you would find that it was not BOS. > If you you are not running FAT that that is a detectable. > If you are running FAT the presence of the GAL (which is not an > allowed FAT label) is also a detectable. > > [YJS] I believe the simultaneous use of FAT and GAL is ruled out by > the TP framework document. > > … > > You say: > "Bottom of stack has been the label position of the PW label for many years, > and this position is mandated by multiple RFCs, e.g. 3985 and 4447 > Note that the PW label must always > be at the bottom of the packet's label stack." > > That is no longer true with the introduction of FAT. > > [YJS] > As you know I proposed an alternative mechanism, > however, in any case the FAT case is different from the GAL. > > Each load balanced flow label is actually a "partial-PW' and thus the flow > label is a type of PW label, > albeit a PW carrying only a subset of the user flows that exist in the > original PW. > > On the other hand the GAL is a modifier, meaning that the rest of the payload > has a different format. > > > Then you say: > > "Present PW implementations receiving the PW label with stack bit cleared, > and a GAL at the bottom position will choke and, at best, discard the packet. > At worst, the GAL may coincide with a legitimate PW label, and the customer > will be > flooded with garbage." > > Your first case is sort of correct - the packet should be silently > discarded as it was clearly not intended for that PW - but it had > better not choke as this would be an attack vector. > > [YJS] By "choke" I meant either discard or flood the impersonated PW with > what it believes to be VCCV packets. > > You second case cannot happen because a GAL is a reserved label and > a reserved label can never be a legitimate PW label. > > [YJS] > My second case CAN happen (I expected this question). > Please remember that before MS-PWs were proposed, PW labels were never > considered "real" MPLS labels, > and many implementations did not religiously apply the MPLS restrictions to > them. > > Stewart > > [YJS] > > I DO have a proposal that is completely consistent with the goals of this > draft AND the PWE RFCs. > > The GAL can be placed in one of 2 positions > > 1)ABOVE the PW label (just as the router alert is placed above the PW > label in VCCV Type 2) > > 2)INSTEAD of the PW label (thus making a single "OAM PW", reducing the > OAM load) > > Note 1 – this is essentially the same as using the GAL for the MPLS > tunnel into which the PWs are placed. > > Note 2 – this is close to my original proposal for PW OAM, that was > abandoned when VCCV "per-PW OAM" won out. > > > > > _______________________________________________ > Ietf mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/ietf _______________________________________________ Ietf mailing list [email protected] https://www.ietf.org/mailman/listinfo/ietf
