Re: [Mpls-interop] MPLS over MPLS-TP

Well, there is a difference IMHO between screwed and screwed.

If you pop a label you may be perfectly happy to continue forwarding on the 
label underneath.
But if you pop the last label (i.e. EOS), you have to go somewhere else to 
find out what to do next.

Of course, that can be screwed as well, but it is perhaps a little less 
likely.

A

----- Original Message ----- 
From: "Ben Niven-Jenkins" <benjamin.niven-jenkins@bt.com>
To: "Malis, Andrew G. (Andy)" <andrew.g.malis@verizon.com>om>; "Adrian Farrel" 
<adrian@olddog.co.uk>uk>; "Drake, John E" <John.E.Drake2@boeing.com>om>; 
<mpls-interop@ietf.org>
Sent: Friday, December 12, 2008 9:40 AM
Subject: Re: [Mpls-interop] MPLS over MPLS-TP

> Andy,
>
> OK I see your point. If the network is screwed up all bets are off.
>
> Ben
>
>
>
> On 11/12/2008 20:11, "Malis, Andrew G. (Andy)" 
> <andrew.g.malis@verizon.com>
> wrote:
>
>> How is it any better for a PW? You still have a label at the top of the
>> stack. There are two scenarios:
>>
>> 1. A label is popped at the MPLS-TP layer that shouldn't have been
>>
>> That's either going to expose another label at that layer that won't be
>> have the proper context, or the start of an IP packet that'll be
>> misinterpreted as a label (since MPLS-TP switches presumably won't know
>> how to forward IP, at least in the fast path). In either case, if
>> there's a matching label allocation to the 20 bits in the header, then
>> it'll be forwarded out a random interface, or dropped if there's no
>> match.
>>
>> 2. An MPLS-TP label wasn't popped that should have been
>>
>> That'll expose (probably) the bottom-most MPLS-TP label to the IP/MPLS
>> client router. Again, what happens next depends on how that label is
>> interpreted by the router.
>>
>> Either way, how are things any better if you use a PW label?
>>
>> Cheers,
>> Andy
>>
>> -----Original Message-----
>> From: Ben Niven-Jenkins [mailto:benjamin.niven-jenkins@bt.com]
>> Sent: Thursday, December 11, 2008 3:03 PM
>> To: Malis, Andrew G. (Andy); Adrian Farrel; Drake, John E;
>> mpls-interop@ietf.org
>> Subject: Re: [Mpls-interop] MPLS over MPLS-TP
>>
>> Andy,
>>
>>
>> On 11/12/2008 15:31, "Malis, Andrew G. (Andy)"
>> <andrew.g.malis@verizon.com>
>> wrote:
>>> AM> The intention would be that the MPLS-TP EOS bit would only be
>>> encountered at boundary the MPLS-TP network, and the payload would
>>> delivered to the client to do with as it desires (and expects),
>> whether
>>> it's IP to forward, MPLS to switch using router-allocated labels, PW
>>> contents, or something else entirely. To the client, there should be
>> no
>>> difference (at some layer of abstraction above the interface details)
>>> between using MPLS-TP for transport and POS or GFP encapsulation for
>>> transport.
>>
>> Yes, but my concern is that IP & MPLS may well be 'recognised' in the
>> network core and if something happened (e.g. Erroneous label pop) to
>> expose
>> them they could be forwarded natively in error.  Other traffic types are
>> unlikely to have this happen as the network core is unlikely to support
>> natively forwarding them.
>>
>> Ben
>>
>
> 

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