John,
I would like to let applications decide how they design the use of the gal.
So I would propose a simple change , that will move any discussions to
the specific applications:
The next text would be as follows:
- Section 4.2. (GAL Applicability and Usage) in [RFC5586], the
original text:
In MPLS-TP, the GAL MUST be used with packets on a G-ACh on
LSPs, Concatenated Segments of LSPs, and with Sections, and
MUST NOT be used with PWs. It MUST always be at the bottom of
the label stack (i.e., S bit set to 1). However, in other MPLS
environments, this document places no restrictions on where
the GAL may appear within the label stack or its use with PWs.
is replaced by:
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.
Does this work ?
Thanks.
Luca
On 08/18/11 08:00, John E Drake wrote:
> Sasha,
>
> I completely agree with your recommendations:
>
> - releasing the bottom-of-stack requirement on GAL
>
> - making use of the statement in RFC 5586 that if GAL is encountered in a packet then G-ACh header MUST be present immediately after the bottom of the label stack (and not immediately after GAL)
>
> - specifying that ECMP on labeled packets MUST ignore reserved labels
>
> Thanks,
>
> John
>
> Sent from my iPhone
>
>> -----Original Message-----
>> From: mpls-bounces@xxxxxxxx [mailto:mpls-bounces@xxxxxxxx] On Behalf Of
>> Alexander Vainshtein
>> Sent: Wednesday, August 17, 2011 9:52 PM
>> To: Luca Martini
>> Cc: mpls@xxxxxxxx; ietf@xxxxxxxx; Vladimir Kleiner; Idan Kaspit;
>> Mishael Wexler; pwe3; Oren Gal; John Shirron; Rotem Cohen
>> Subject: Re: [mpls] [PWE3] IETF Last Call comment on draft-ietf-pwe3-
>> gal-in-pw
>>
>> Luca and all,
>> I have not found the statement you've proposed in draft-ietf-pwe3-fat-
>> pw-06. Instead, it contans the following text in Section 8.5 "
>> Applicability to MPLS-TP":
>>
>> <quote>
>> The flow aware transport of a PW reorders packets, therefore MUST
>> NOT be
>> deployed in a network conforming to the MPLS-TP unless these
>> integrity requirements
>> specified in the SLA can be satisfied.
>> <end quote>
>>
>> (In the -07 version this text is repeated but followed by an incomplete
>> statement " In a" immediately followed by the heading of Section 8.6.
>> Since this addition is difficult to parse, I will ignore it for the
>> moment.)
>>
>> IMHO and FWIW this means that prohibition on using flow aware PW in
>> MPLS-TP environments is conditional on meeting specific SLA
>> requirements for the service. So I think that the use case I've
>> presented still holds.
>>
>> Please note also that, regardless of the restriction in draft-ietf-
>> pwe3-fat-pw, be it conditional or absolute, usage of flow labels in an
>> MPLS-TP domain would be perfectly safe if ECMP (i.e., hashing of the
>> label stack and taking one of multiple NHLFEs for the given incoming
>> label in the ILM) were not used in this domain, e.g., by associating
>> exactly one ILM entry with each incoming label in the ILM. And since
>> MPLS-TP is supposed to carry not just PW clients but also IP ones, I
>> would expect that this would be the case in any MPLS-TP deployment.
>>
>> I also think that releasing one restriction (on using GAL in PWs) at
>> the expense of making another, conditional one (on usage of flow labels
>> in MPLS-TP environments) absolute is not the most appropriate method
>> for resolving technical issues. IMHO and FWIW better way to resolve the
>> problem would be by:
>>
>> - releasing the bottom-of-stack requirement on GAL
>> - making use of the statement in RFC 5586 that if GAL is encountered in
>> a packet then G-ACh header MUST be present immediately after the bottom
>> of the label stack (and not immediately after GAL)
>> - specifying that ECMP on labeled packets MUST ignore reserved labels.
>>
>> I think that these considerations have been presented already in the
>> discussion on draft-nadeau-pwe-vccv-2.
>>
>> Of course it would be even better if we could agree on transition to
>> universal usage of the CW and VCCV Type 1 in PWs. But this is a
>> different story.
>>
>> Regards,
>> Sasha
>> ____________________________________
>> From: Luca Martini [lmartini@xxxxxxxxx]
>> Sent: Wednesday, August 17, 2011 9:58 PM
>> To: Alexander Vainshtein
>> Cc: Pablo Frank; mpls@xxxxxxxx; ietf@xxxxxxxx; Vladimir Kleiner; Idan
>> Kaspit; Mishael Wexler; pwe3; Oren Gal; John Shirron; Rotem Cohen
>> Subject: Re: [PWE3] IETF Last Call comment on draft-ietf-pwe3-gal-in-pw
>>
>> The solution is quite simple:
>>
>> "Flow Labels MUST not be used in an MPLS-TP environment."
>>
>> Luca
>>
>>
>>
>>
>>
>> On 08/16/11 21:46, Alexander Vainshtein wrote:
>>> Pablo,
>>> Sorry, but I think you're wrong. Only T-PE can insert the flow label
>>> (because only T=PE can be "flow-aware"). S-PE simply performs swap on
>>> PW label.
>>>
>>> Regards,
>>> Sasha
>>>
>>> ---------------------------------------------------------------------
>> ---
>>> *From:* Pablo Frank [pabloisnot@xxxxxxxxx]
>>> *Sent:* Wednesday, August 17, 2011 12:17 AM
>>> *To:* Alexander Vainshtein
>>> *Cc:* ietf@xxxxxxxx; mpls@xxxxxxxx; Vladimir Kleiner; Idan Kaspit;
>>> Mishael Wexler; pwe3; Oren Gal; John Shirron; Rotem Cohen
>>> *Subject:* Re: [PWE3] IETF Last Call comment on draft-ietf-pwe3-gal-
>> in-pw
>>> I think it's okay because as the PW crosses the ECMP-enabled IP/MPLS
>>> domain in the middle segment, you're no longer in an MPLS-TP
>>> environment and so the GAL is not required to be BOS. During that
>>> middle segment, the PW flow label would be placed below the GAL and
>>> above the GACh. It gets removed when it hits the S-PE that switches
>>> you back into the MPLS-TP environment. In other words, whether
>> you're
>>> in an MPLS-TP environment is determined segment by segment in a MS-
>> PW.
>>> Pablo
>>>
>>> On Tue, Aug 16, 2011 at 1:02 PM, Alexander Vainshtein
>>> <Alexander.Vainshtein@xxxxxxxxxxx
>>> <mailto:Alexander.Vainshtein@xxxxxxxxxxx>> wrote:
>>>
>>> Hi all,
>>> After having sent out my comments I've noticed that the specific
>>> example to illustrate the need to combine GAL and "flow label"
>> was
>>> inaccurate.
>>>
>>> A more relevant example would look like following (I do not
>>> include a diagram, but it can be easily provided if necessary)
>>>
>>> 1. A MS-PW:
>>> * Starts at an S-PE that resides at the edge of an MPLS-TP
>>> domain (no ECMP)
>>> * Crosses this domain and enters an IP/MPLS domain with
>> ECMP
>>> enabled using a T-PE that resides at the age of these two
>>> domains
>>> * Leaves this domain and enters a 2nd MPLS-TP domain (using
>>> the 2nd T-PE)
>>> * Terminates on another S-PE at the edge of the 2nd MPLS-TP
>>> domain
>>> 2. 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. Note that:
>>> * This does not violate the MPLS-TP restriction on ECMP:
>>> ECMP does not happen in he MPLS-TP domains
>>> * T-PEs do not even have to be aware of flow labels
>>> 3. The operator also intends to operate some end-to-end OAM for
>>> this MS-PW using "GAL-in-PW". This results in a conflict
>> since
>>> both GAL and "flow label" are defined (in the corresponding
>>> drafts) as bottom of stack.
>>>
>>>
>>>
>>> IMHO this describes a realistic scenario where the two drafts are
>>> in controversy.
>>>
>>> Regards,
>>> Sasha
>>> -----------------------------------------------------------------
>> -------
>>> *From:* mpls-bounces@xxxxxxxx <mailto:mpls-bounces@xxxxxxxx>
>>> [mpls-bounces@xxxxxxxx <mailto:mpls-bounces@xxxxxxxx>] On Behalf
>>> Of Alexander Vainshtein [Alexander.Vainshtein@xxxxxxxxxxx
>>> <mailto:Alexander.Vainshtein@xxxxxxxxxxx>]
>>> *Sent:* Tuesday, August 16, 2011 4:26 PM
>>> *To:* ietf@xxxxxxxx <mailto:ietf@xxxxxxxx>
>>> *Cc:* mpls@xxxxxxxx <mailto:mpls@xxxxxxxx>; Vladimir Kleiner;
>> Idan
>>> Kaspit; Mishael Wexler; pwe3; Oren Gal; John Shirron; Rotem Cohen
>>> *Subject:* [mpls] IETF Last Call comment on draft-ietf-pwe3-gal-
>> in-pw
>>> Hi all,
>>>
>>>
>>>
>>> I would like to raise the following issue with regard to
>>> draft-ietf-pwe3-gal-in-pw
>>> <http://datatracker.ietf.org/doc/draft-ietf-pwe3-mpls-tp-gal-in-
>> pw/?include_text=1>:
>>> controversy vs. draft-ietf-pwe3-fat-pw
>>> <http://datatracker.ietf.org/doc/draft-ietf-pwe3-fat-
>> pw/?include_text=1>
>>> with regard to bottom-of-stack position.
>>>
>>>
>>>
>>> As stated in the Introduction, this draft removes the restriction
>>> imposed by RFC 5586 on usage of Generic Associated Channel Label
>>> (GAL) in PWs. The corresponding text Section 4.2 of RFC 5586
>> states:
>>> In MPLS-TP, the GAL MUST be used with packets on a G-ACh on LSPs,
>>> Concatenated Segments of LSPs, and with Sections, and MUST NOT be
>>> used with PWs. It MUST always be at the bottom of the label
>> stack
>>> (i.e., S bit set to 1).
>>>
>>>
>>>
>>> draft-ietf-pwe3-gal-in-pw proposed to replace the original text
>> in
>>> RFC 5586 with the following
>>>
>>>
>>>
>>> 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. It MUST always be at the bottom of the label stack
>>> (i.e., S bit set to 1).
>>>
>>>
>>>
>>> I.e., while removing this restriction of 5586, it does not
>> modify
>>> its requirement for the GAL being always at the bottom of the
>>> label stack.
>>>
>>>
>>>
>>> At the same draft-ietf-pwe3-fat-pw (currently also in the IESG
>>> review) reserves the bottom of the PW stack for the PW flow
>>> labels, e.g., in Section 1.1:
>>>
>>>
>>>
>>> This document describes a method of adding an additional label
>>> stack entry (LSE) at the bottom of stack in order to facilitate
>>> the load balancing of the flows within a PW over the available
>>> ECMPs.
>>>
>>>
>>>
>>> One could argue that draft-ietf-pwe3-gal-in-pw only applies to
>>> MPLS-TP pseudowires, and that MPLS-TP does not use ECMP. IMHO and
>>> FWIW,
>>>
>>> such an argument, were it presented, would be highly problematic,
>>> because:
>>>
>>>
>>>
>>> 1. RFC 5960 (which defines the MPLS-TP data plane) did not
>>> define any differences between the PW data plane in IP/MPLS and
>>> MPLS-TP.
>>>
>>> 2. One of the most popular scenarios for using multi-
>> segment
>>> pseudowires is the case when an edge-to-edge service emulation
>>> crosses multiple IP/MPLS and MPLS-TP domains. In these scenarios,
>>> the flow label of draft-ietf-pwe3-fat-pw (inserted by a flow-
>> aware
>>> T-PE at the edge of an IP/MPLS domain) would potentially compete
>>> with GAL (inserted by a T-PE at the edge of an MPLS-TP domain,
>>> e.g., for relying a PW status message that it has received over a
>>> Targeted LDP session from the IP/MPLS domain to a static PW
>> status
>>> message to cross the MPLS-TP domain) for the bottom-of-stack
>>> position.
>>>
>>>
>>>
>>> The issue I am raising Is not new. It has been actively discussed
>>> on the PWE3 mailing list with regard to adoption of
>>> draft-nadeau-pwe3-vccv-2 as a WG document, with arguments for
>>> both the flow label and GAL taking the bottom-of-the-stack
>>> position. But, to the best of my understanding, consensus on this
>>> issue has not been reached.
>>>
>>>
>>>
>>> Hopefully this comment will be useful.
>>>
>>>
>>>
>>> Regards,
>>>
>>> Sasha
>>>
>>>
>>>
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