Subject: Wildcard session management messages

From: Skip Booth <[email-masked]>
Date: Fri, 7 Sep 2001 16:38:09 -0400

In reading through the new L2TPv3 draft and the Martini draft
(draft-martini-l2circuit-trans-mpls-07.txt), I realized that in L2TP we
don't have anything analogous to the "wild card label withdraw procedure"
as defined in Martini.  Using L2TP terminology, the wildcard label
procedure effectively allows a LCCE to tear down a group of sessions using
an arbitrary group id.  The group id serves as a means to group a set of
sessions together.  Today, the only way to do this is to manage the set of
sessions in the same tunnel and send a STOPCCN to teardown all of the
sessions.

In L2TPv3 (or v2 for that matter), the private group id could certainly
suffice as the "group id" defined in the Martini draft.  However, the CDN
currently doesn't allow for a "wildcard" interpretation.  One suggestion
might be to send the private group id in the ICRQ/OCRQ message along with
the assigned session id.  A wildcard CDN would be sent with the assigned
session id avp either not present or set to 0, and the private group id set
to whatever group of sessions you wish to teardown.  The receiver of this
message would then perform a lookup on the group id to determine what
sessions need to be destroyed.

I don't believe using a STOPCCN is really a good solution for this problem
since it forces you to create multiple tunnels between the same two peers
to represent each group.

The alternative is to send a CDN for each session in the group.  This is
really a waste of messages when handling an event such as an interface
transition which affects every session on that interface.  Then again,
that's what we have been doing for a while now, so maybe the extra messages
are not that expensive.

One of my peers also asked whether we would want the ability to do wildcard
messages for other session management messages.  The usefulness of this
isn't as apparent to me but we can certainly debate this.

Comments?  Should this be incorporated into the L2TPv3 draft?

Thanks,
-Skip