Subject: Re: PWE3 requirements

From: "Andrew G. Malis" <[email-masked]>
Date: Tue, 01 Apr 2003 11:01:30 -0500

Stewart,

>Yes, it's a difficult call. I don't want to disrupt the document
>and I too am concerned about how late in the day we realised the
>need to do this. On the other hand I am also concerned that folks
>could argue that the issue is OOS because it unless it is in the
>requirements.

Was the realization for this need as a result of experience in the field 
with core routers with ECMP enabled?  If so, reporting the field experience 
would help to scope the requirement.

Thanks,
Andy

---

From: Mustapha Aissaoui <[email-masked]>
Date: Thu, 03 Apr 2003 12:31:52 -0500

Tom,

"Thomas D. Nadeau" wrote:
> 
> >The Requirements document says nothing about the issue
> >of a PW aliasing an IP packet (the CW PID issue). It
> >is clear from comments on the list that a PW that
> >does not take this into account will be subject to
> >disruption when traversing an ECMP enabled MPLS core, and
> >I raised concerns about psamp/ipfix.
> >
> >I think that there needs to be a requirement added to
> >to the effect that a PW must operate correctly over a PSN
> >that provides ECMP, and a possibly a requirement that
> >allows IP flow monitoring. Whether this gets resolved in
> >PWE3 or in MPLS is OoS, but as PWE3 is the first payload
> >that he IETF has defined that has this problem, it
> >generates the requirement.
> >
> >Something like:
> >
> >"If the PSN uses an ECMP or IP flow recognition method,
> >then the PW encapsulation must use a method discriminating
> >between itself and an IP flow"
> 
>          I think that it is hard to determine if the PSN
> employs an ECMP or flow recognition method other
> that knowing a priori that they might exist.  I think it
> might be more straight-forward to just state,
> 
>          "The PW encapsulation must use a method whereby
> any PW can be distinguished from other flows traversing the
> PSN."
> 
>          That seems to cover all the cases.

Your sentence generalizes the issue beyond what the stated issue
was. What was stated was to make sure that the PSN does not
misinterpret a PW payload for a IPv4 or IPv6 packet in some specific
situations (ECMP was one). We are not saying that the core nodes
require to distinguish a PW from some other TBD payload, which may
not be relevant to it (e.g., OAM messages).

Therefore, I suggest that we stick to Stewart's original sentence.

Regards,
Mustapha.

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From: "Thomas D. Nadeau" <[email-masked]>
Date: Thu, 03 Apr 2003 13:43:51 -0500

>not be relevant to it (e.g., OAM messages).

         My suggestion says nothing about core or edge or otherwise
nodes and neityher does the original one. The implicit assumption is
that the PW encapsulation not violate the forwarding behavior of
existing MPLS or IP P routers.

         --Tom

>_______________________________________________
>pwe3 mailing list
>[email-masked]
>https://www1.ietf.org/mailman/listinfo/pwe3

http://www.elsevier-international.com/catalogue/title.cfm?ISBN=155860751X

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From: Mustapha Aissaoui <[email-masked]>
Date: Thu, 03 Apr 2003 14:27:37 -0500

> existing MPLS or IP P routers.

Yes, but your statement says that a router has to be able to
distinguish a PW from any other payload type, not just IP. This is
not required at all.

---

From: "Thomas D. Nadeau" <[email-masked]>
Date: Thu, 03 Apr 2003 14:47:35 -0500

>distinguish a PW from any other payload type, not just IP. This is

         Again, I don't see how the original statement or my refined
one say anything about any router or packet handling. They both
state that the format must allow for the packet to be self-describing
so that it can be distinguished from other types of traffic.

         --Tom

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From: Stewart Bryant <[email-masked]>
Date: Fri, 04 Apr 2003 11:38:25 +0100

> distinguish a PW from any other payload type, not just IP. This is

At the moment we only have 3 payload types, IPv4, IPv6 and PW.
We cannot make the assumption that there will not be another
of interest to a core router at some time in the future.

This issue arrises in PWE3, not because PWs are special, but
because they are the first non-IP MPLS payload standardised
by the IETF.

Stewart

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From: Mustapha Aissaoui <[email-masked]>
Date: Fri, 04 Apr 2003 12:41:48 -0500

Stewart,

> because they are the first non-IP MPLS payload standardised

I agree that we cannot make that assumption. This is why I suggest
that we resolve the issue of protocol identification in broader
context than the current IP aliasing issue. 

So far I have seen the following three issues raised:

1. IP aliasing: making sure that PW wire traffic does not get
mistaken for an IPv4 or an IPv6 packet when ECMP or some sort of
load-balancing is applied.

2. Making sure that PW OAM messages are identified properly from
user packets in a PE. Then make sure they traverses the same path as
user traffic, again in the case of ECMP or load-balancing.

3. Allow for more than one protocol in the pseudo-wire. I have
customers telling me that their customers have a mix of protocols in
the same VC in the current FR/ATM L2 services (mix of bridged and
routed PDUs where bridged does not mean it is always Ethernet). In
many cases, these service providers cannot make assumptions about
what their customers are carrying in a VC (this is what a L2 service
is about in the first place).

Regards,
Mustapha.