AII differences between PW routing and l2vpn signalling draft provisionong methods.

Luca Martini <lmartini@cisco.com> Fri, 02 December 2005 18:09 UTC

Message-ID: <43908DBC.8000000@cisco.com>
Date: Fri, 02 Dec 2005 11:09:00 -0700
From: Luca Martini <lmartini@cisco.com>
User-Agent: Mail/News 1.4 (X11/20050929)
MIME-Version: 1.0
To: L2VPN <l2vpn@ietf.org>
Content-Type: text/plain; charset="ISO-8859-1"; format="flowed"
Content-Transfer-Encoding: 7bit
Content-Transfer-Encoding: 7bit
Cc: David McDysan <dave.mcdysan@mci.com>, bsd@cisco.com
Subject: AII differences between PW routing and l2vpn signalling draft provisionong methods.
Precedence: list
Sender: l2vpn-bounces@ietf.org
Errors-To: l2vpn-bounces@ietf.org

WG,

After a good discussion with Bruce Davie,  we came up with the following 
explanation on why we need to have different AII type int he PW setup 
and maintenance protocol.
This note explains why draft-ietf-l2vpn-signaling-06.txt (the L2VPN 
Signaling draft) and draft-balus-bocci-martini-dyn-ms-pwe3-00.txt (the 
MS PW draft) make use of different AII types, as defined in 
draft-metz-aii-aggregate-01.txt.
 In a nutshell, the two drafts use different AII types because they are 
tackling different problems. Specifically, L2VPN Signaling draft is 
concerned with setting up all the PWs for a given L2VPN, while the MS PW 
draft is concerned with setting up individual PWs.
 Because it is concerned with building L2VPNs, the L2VPN Signaling draft 
makes use of the AGI (the contents of which effectively identify the 
VPN) plus the AII to identify a particular PW. Hence, the AII only needs 
to identify a "pool" or a VSI relative to a particular AGI. Hence a 
simple 32 bit AII is sufficient.
By contrast, because the MS PW draft is concerned with setting up 
individual PWs, not L2VPNs, it has no use for the AGI - there is no 
"group" concept. Hence it fully identifies the PW in the AII. Because 
there may be many PWs connected to a given U-PE device, it is necessary 
to identify the PWs relative to a given U-PE. And it is necessary to 
identify the U-PE within the AII so that the signaling message can be 
routed toward the correct U-PE. Hence the requirements for the AII are 
quite different, and it makes sense to use an AII type that is designed 
to meet these requirements.
It is obvious that the simple AII type could be encoded in the more 
complex AII type by leaving various fields set to zero, but this does 
not seem to serve any useful purpose.

Luca

AII differences between PW routing and l2vpn sign… Luca Martini
RE: AII differences between PW routing and l2vpn … Mustapha Aissaoui