RE: [mpls] [PWE3] IETF Last Call comment on draft-ietf-pwe3-gal-in-pw

Alexander Vainshtein <Alexander.Vainshtein@xxxxxxxxxxx> · Fri, 2 Sep 2011 18:02:12 +0300

Matthew,
Lots of thanks for a prompt response.

Please see a couple of comments inline below.

Regards,
     Sasha

From: Bocci, Matthew (Matthew) [matthew.bocci@xxxxxxxxxxxxxxxxxx]

Sent: Friday, September 02, 2011 1:06 PM

To: Alexander Vainshtein; Stewart Bryant

Cc: Yaakov Stein; mpls@xxxxxxxx; pwe3; iesg@xxxxxxxx; pwe3-chairs@xxxxxxxxxxxxxx; Luca Martini; IETF Discussion

Subject: Re: [mpls] [PWE3] IETF Last Call comment on draft-ietf-pwe3-gal-in-pw

Sasha,

On your final comment on the concept of an MPLS-TP PW, RFC5586 has already made the distinction between the use of the GAL on PWs in MPLS-TP and in other MPLS environments. This draft aligns the two cases in terms of the applicability of the GAL, by updating
 RFC5586 to remove the restriction on its use and position in an MPLS-TP environment. 

[[Sasha]] IMHO and FWIW this is one more indication that there is no such thing as an MPLS-TP PW as different from an MPLS TP. Did I miss something important?

The case of interconnecting PW segments on MPLS-TP to PW segments on general MPLS networks should be discussed elsewhere, IMHO, as the interaction between the GAL and hashing on some PW segments is most likely not the only issue.

[[Sasha]] Sounds OK with me.

RFC5921 rules out the use of ECMP in MPLS-TP networks, so one would not expect an MPLS-TP PSN to hash the flow label today.

[[Sasha]] I make a distinction between inserting a flow label at T-PE and hashing on the label stack (or lack thereof) in some of the network domains that are crossed by the MS-PW packet. The hashing is
 done (or not done) by P routers that do not specifically care about PWs.

If that is going to change or if there are other flow label applications in MPLS-TP, then IMHO drafts detailing those applications should discuss the interaction with the GAL. 

[[Sasha]] Please see above. IMHO there is no need for a new application to study the interaction.

Regards,

Matthew

On 02/09/2011 06:05, "Alexander Vainshtein" <Alexander.Vainshtein@xxxxxxxxxxx> wrote:

Stewart,
Lots of thanks for a prompt response.

My original email contained a typo (S-PE instead of T-PE  named as inserting ) which I've acknowledged and corrected in this thread (please see

http://www.ietf.org/mail-archive/web/pwe3/current/msg12586.html).

With this correction in mind, the example I've presented (an MS-PW that originates in a T-PE in a MPLS-TP domain and them crosses - at S-PE - into an IP/MPLS domain) matches, IMHO, Yaakov's question. And if the operator wishes
 to improve traffic distribution in the IP/MPLS domain which employs ECMP, flow labels would be inserted by T-PE.

I believe that the change in draft-ietf-pwe3-gal-in-pw that you've proposed inhttp://www.ietf.org/mail-archive/web/pwe3/current/msg12613.html resolves
 the original issue I've raised of both GAL and flow label "competing" for the BoS position. 

However, a conceptual question - can any MPLS-TP restrictions be placed on PWs?- remains open as noted in Greg's comment (please see

http://www.ietf.org/mail-archive/web/pwe3/current/msg12620.html). IMHO and FWIW we should acknowledge the fact (implicitly recognized  already in RFC 5920) that
there is simply no such thing as a MPLS-TP PW.

Hopefully this note clarifies my position on the subject.

Regards, and apologies for the original typo,
     Sasha

From: Stewart Bryant [stbryant@xxxxxxxxx]

Sent: Thursday, September 01, 2011 8:33 PM

To: Alexander Vainshtein

Cc: Yaakov Stein; mpls@xxxxxxxx; pwe3; 
iesg@xxxxxxxx; pwe3-chairs@xxxxxxxxxxxxxx; Luca Martini; IETF Discussion

Subject: Re: [mpls] [PWE3] IETF Last Call comment on draft-ietf-pwe3-gal-in-pw

On 01/09/2011 17:07, Alexander Vainshtein wrote:

Yaakov,
You've written 

PW that starts in an MPLS-TP domain,
can easily leak into a non-TP domain

This is exactly the point that I've raised in my IETF LC comment on the draft (for MS-PW) - please see my email (to several lists) that explains that in some detail, at
 http://www.ietf.org/mail-archive/web/pwe3/current/msg12581.html.

Regards,

Sasha

The operator intends to improve traffic distribution in the IP/MPLS domain, hence he enables insertion and discard of "flow labels" at the two S-PEs.

Speaking as an author of the FAT-PW draft I do not recall any text that proposes that S-PEs insert FLs in the stack, and it never occurred to me that anyone anyone would try, since would require a change to the design of the S-PEs.

Stewart

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