Subject: RE: VPN Identifiers

From: [email-masked]
Date: Wed, 13 Aug 2003 07:50:35 +0100

> Eric:
> With regard to the requirements you've  stated, I don't think 
> it matters how many different methods there are for  producing 
> VPN-ids, as long as there is no ambiguity introduced into the 
> encodings. 

I agree, but only if the same encodings are supported by all the VPN drafts.
For example, lets say a network operator decides that they want to deploy a
VPLS service today using BGP auto-discovery along with LDP signalling. BGP
auto-discovery has an 8 byte field that can be used to encode an RFC2685 VPN
ID, but the LDP signalling draft currently uses has a 4 byte VC ID to
identify a VPN. So what VPN ID format should the operator use? The
alternatives seem to be i) use 4 byte VPN ID in both, or ii) use two
different VPN IDs and map/translate between the two. Option i) has
scalability/global uniqueness issues and option ii) requires multiple VPN
IDs to be provisioned/managed. If there are operators that have deployed
VPLS using a combination of these two mechanisms or there are alternative
options then I would be interested in hearing about them.

Looking at things from a vendors perspective specifying a single VPN ID
format would make implementation simpler/cheaper. Looking at things from an
operators perspective as long as ALL the VPN ID formats are supported by ALL
the VPN protocols/systems that need to use VPN IDs then there is no issue.
The provider can just select whichever VPN ID meets their requirements
without having to worry about which mechanisms support which VPN ID format.
The issues arises when the operator has to manage multiple VPN IDs or
perform VPN ID translation because the mechanisms/systems the operator wants
to implement use different VPN ID formats.

Richard

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From: "W. Mark Townsley" <[email-masked]>
Date: Wed, 13 Aug 2003 14:46:37 +0200

> to implement use different VPN ID formats.

Ambiguity between VPN ID formats or not, isn't the real point that you can't 
turn 8 octets into 4 without losing a significant amount of information? The 
showstopper I see here is with the unacceptably low common denominator 
introduced by the 4 octet VCID used by LDP signaling today more than anything else.

draft-rosen-ppvpn-l2-signaling-03.txt addresses the current LDP limitation, and 
L2TPv3 has used a variable length endpoint identifier since day one. Perhaps the 
4-octet IDs should be banished to manual setup only, and the 8+ octet format(s) 
used for pseudowires setup via auto-discovery.

- Mark