Re: [PWE3] GAL above and below the PW label

Sriganesh, Curtis and all,
IMHO and FWIW I think that the only problem with VCCV Type 3 is the risk of OAM packets leaking out of T-PE towards the AC (if you accidentally set the TTL value too high). To the best of my understanding the offset proposal does not solve that - or did I miss something?

One way to solve it is to use VCCV Type 1 (clean where applicable).
Another way would be by using GAL below the PW label (possible but messy). If the industry moves towards deprecating Ethernet PWs without CW,  it becomes completely unnecessary.

My 2c,
     Sasha

> -----Original Message-----
> From: pwe3-bounces@ietf.org [mailto:pwe3-bounces@ietf.org] On Behalf Of
> Sriganesh Kini
> Sent: Thursday, March 31, 2011 10:09 AM
> To: curtis@occnc.com
> Cc: pwe3@ietf.org
> Subject: Re: [PWE3] GAL above and below the PW label
> 
> All,
> 
> Just an FYI that a proposal for fate-sharing PW OAM and data given in
> draft-kini-pwe3-inband-cc-offset
> 
> Just to summarize the proposal.
> 1. It does not require GAL in PW. TTL expiry is used to alert the S/T-
> PE.
> 2. It is mainly applicable when CW is not used in the PW.
> 3. It uses a fixed offset (negotiated between PW endpoints) after the
> label stack before starting the OAM msg.
> 4. The bytes between the label-stack and the fixed offset is referred
> to as a pseudoflow header and is filled with byte-values (by the PE)
> that represent the flow for which OAM is desired. This helps PW OAM
> and data to fate-share even when the intermediate node looks beyond
> label stack to do multipath forwarding decisions.
> 
> 
> On Thu, Mar 31, 2011 at 12:03 AM, Curtis Villamizar <curtis@occnc.com>
> wrote:
> >
> > Loa, Dave, Sasha,
> >
> > I've snipped from various posts on the thread that Sasha started.
>  See
> > inline.
> >
> > In message <4D92F5D3.6080609@pi.nu>
> > Loa Andersson writes:
> >>
> >> All,
> >>
> >> missed a nuance in Sasha subject line.
> >>
> >> We have two issues
> >>
> >> - where the GAL is placed relative to the PW label, I  believe it is
> >>    necessary to have the GAL below the PW label.
> >>
> >> - whether the the GAL label needs to be bottom of stack or not, it
> >>    figure that this is really a discussion if it is possible to have
> >>    a FAT label below the GAL or not. I'm not sure  about my
> preferences
> >>    but I think it is possible.
> >>
> >> /Loa
> >
> > I agree with Loa's summary.  Not putting GAL at the bottom may
> confuse
> > some LSR, but putting it above the PW label is likely to be even more
> > problematic.
> >
> >
> > In message
> <60C093A41B5E45409A19D42CF7786DFD51D5310B53@EUSAACMS0703.eamcs.ericsson
> .se>
> > David Allan I writes:
> >>
> >> It does become a new behavior, GAL with S=3D0. However the
> combination of G=
> >> AL being top label at the S-PE and TTL being encoded in the PW label
> means =
> >> that fate sharing is broken at every S-PE. Life only gets a little
> more str=
> >> ange if there is a FAT label as well...
> >>
> >> That being said, GAL as bottom label is broken in any ECMP
> environment, whi=
> >> ch is why GAL is a TP construct.
> >>
> >> my 2 cents
> >> D
> >
> > Dave,
> >
> > If GAL is broken for ECMP, which it is, then all TP OAM is broken.
> > If all it takes to fix it is simple then lets just fix it.
> >
> > This is what we'd have to do.
> >
> >  1) Relax the requirement that GAL be at the bottom
> >
> >  2) Have the ingress insert GAL in the stack immediately below the
> >     label for which the measurement is made, keeping the rest of the
> >     label stack in place.
> >
> > The only thing the midpoing LSR at a multipath (LAG, link bundle for
> > MPLS) has to do is skip over the GAL when hashing, as if the GAL
> > wasn't there.  That will yield the same hash value and it will
> > preserve fate-sharing across multipath.
> >
> > I prefer that we fix things rather than complain that they are
> broken.
> >
> > Curtis
> > _______________________________________________
> > pwe3 mailing list
> > pwe3@ietf.org
> > https://www.ietf.org/mailman/listinfo/pwe3
> >
> 
> 
> 
> --
> - Sri
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