Subject: [L2tpext] draft-ietf-l2tpext-failover-01 query

From: "Chris Hellberg" <[email-masked]>
Date: Sun, 27 Jul 2003 03:17:13 +1200

Hi,

Does anyone have any code or reports of trials with the mechanism? I've been having a few thoughts on the passing of state between a LAC and two LNSs. With the failover mechanism, there's a concept of hinting to the "backup" LNS on the session ID it would prefer to use. 

Would I be correct in thinking that the passing of upper-layer state information (such as IP address for an IPv4-encapsulated tunnel, DNS, WINS, etc) would need to be handled by upper-layer protocols such as PPP? 

Would this also mean that most PPP implementations would need to cope with suddenly having to start LCP again in the middle of a session, or does this capability happen with most stacks today anyway?

Cheers,

Chris

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From: Vipin Jain <[email-masked]>
Date: Mon, 28 Jul 2003 10:41:13 -0700 (PDT)

my comments inline..

> Does anyone have any code or reports of trials with the mechanism?
There were some (I worked on one) proprietary implementations circling around
the mechanism. The draft has also changed significantly from its first rev.

> I've been having a few thoughts on the passing of state between
> a LAC and two LNSs.
I assume. by 'state' you mean the state of an L2TP session, which is 'Idle',
'Established', 'Wait-Tunnel', 'Wait-Connect', or 'Wait-Reply'. Failover
mechanism described in the mentioned draft doesn't aim at recovering sessions
that were not in 'Established' state. Do you suggest we could preserve the
sessions that were in semi established state and recover them as well to help
the restart process?

> With the failover mechanism, there's a concept
> of hinting to the "backup" LNS on the session ID it would prefer to use.  The
draft today requires that the 'backup' LNS MUST use the same 'session ID'
otherwise the recovery of a session is not possible. Are you suggesting that
the mechanism to switch session ids would give some benefits? IMHO it would be
more messy, specially because failover node's peer would have to switch the
traffic to the new session id then.

> Would I be correct in thinking that the passing of upper-layer state
> information (such as IP address for an IPv4-encapsulated tunnel, DNS, WINS,
> etc) would need to be handled by upper-layer protocols such as PPP? 
If session id remains same, there is no need for PPP renegotiations. The sesion
would simply work as if nothing failed on the other side, except a small hiccup
in the data path.

> Would this also mean that most PPP implementations would need to cope with
> suddenly having to start LCP again in the middle of a session, or does this
> capability happen with most stacks today anyway?
I think it should be transparent to PPP layer. Why do you think there is a need
to restart LCP?

thanks,
-- vipin

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From: Vipin Jain <[email-masked]>
Date: Mon, 28 Jul 2003 10:41:13 -0700 (PDT)

my comments inline..

thanks,
-- vipin