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Re: [PWE3] [mpls] Response to Liaison on Clarifying P2MP Combinations

Eric Gray <eric.gray@ericsson.com> Tue, 26 November 2013 14:45 UTC

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From: Eric Gray <eric.gray@ericsson.com>
To: Loa Andersson <loa@pi.nu>, "huubatwork@gmail.com" <huubatwork@gmail.com>, "Bocci, Matthew (Matthew)" <matthew.bocci@alcatel-lucent.com>, "pwe3@ietf.org" <pwe3@ietf.org>
Thread-Topic: [mpls] [PWE3] Response to Liaison on Clarifying P2MP Combinations
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Date: Tue, 26 Nov 2013 14:45:28 +0000
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References: <CEB45EA6.580D2%matthew.bocci@alcatel-lucent.com> <5290BEFC.20308@gmail.com> <5292A5F7.3010609@pi.nu> <48E1A67CB9CA044EADFEAB87D814BFF6329A3272@eusaamb107.ericsson.se> <529420AD.5080405@pi.nu>
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Subject: Re: [PWE3] [mpls] Response to Liaison on Clarifying P2MP Combinations
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Loa,

	I think you mean on a per-segment basis, where a group of PW-branches
would traverse the segment using the same segment-ingress/egress pair, right?

	If so, this is not logically different from having the same set of PW-branches
traversing a common link.  I guess it is possible that a P2MP MS-PW would only use 
P2P LSPs in every segment; that would require every branching point to be at the
points where the P2P LSP in one domain terminates and two or more P2P LSPs are
used to forward distinct subsets of the P2MP PW through the next domain.  This
seems likely (to me, anyway) only if the LSR at the domain boundary belongs to
both domains (not the common case, I believe).  

	If there was no branching at domain boundaries, and no P2MP LSPs in any 
domain, it beggars the imagination as to why a P2MP PW would be used in the first 
place, so the overall set of LSPs would effectively be P2MP - wouldn't they?

	But, if you think transport of a P2MP PW over a set of P2P LSPs exclusively 
is a valid scenario to consider, why include the text in question at all?

	Since you snipped it, I am adding back the text in question.  It says:

  " The only current valid case for P2MP PWs is when used with corresponding P2MP 
    LSPs, as described in the draft referenced above."

	The primary message in this text is that carrying a P2MP PW over anything 
other than a P2MP LSP is invalid.  If that is not the clarification we want to provide,
then we need to change this text, or remove it.

--
Eric

-----Original Message-----
From: Loa Andersson [mailto:loa@pi.nu] 
Sent: Monday, November 25, 2013 11:17 PM
To: Eric Gray; huubatwork@gmail.com; Bocci, Matthew (Matthew); pwe3@ietf.org
Cc: mpls@ietf.org
Subject: Re: [mpls] [PWE3] Response to Liaison on Clarifying P2MP Combinations
Importance: High



<snip>
> 2) use of a P2MP PW in conjunction with one or more P2P LSPs is definitely not
>       valid.
>
snip>

Well a MS-PW could do P2MP over P2P LSPs, right?

/Loa

-- 


Loa Andersson                        email: loa@mail01.huawei.com
Senior MPLS Expert                          loa@pi.nu
Huawei Technologies (consultant)     phone: +46 739 81 21 64

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