Subject: RE: How to Reorder/Detect packet loss in case of Payload L2TP pa ckets?

From: William Dixon <[email-masked]>
Date: Fri, 14 Apr 2000 20:46:19 -0700

Barney, I mistakenly thought we could agree on a convention, after rereading
the spec..., I now see that if requested they must be present, so for
interop I must support sequence numbers.  The other reason I had for packet
loss calculated in the IPSec module was to still get packet loss
measurements when implementing header compression.

From the L2TPHC draft:
The S bit MUST be set to 0, indicating no Nr/Ns fields.  Control
   packets are not passed via L2TPHC.  If sequencing of data packets is
   required, L2TPHC MUST NOT be used for those data packets.  

Clearly in this case, if you negotiated L2TPHC, then there are no L2TP
sequence numbers, yet packet loss figures could still be tracked for the
L2TP/IPSec sessions.

-----Original Message-----
From: Barney Wolff [mailto:[email-masked]]
Sent: Friday, April 14, 2000 6:41 PM
To: [email-masked]
Subject: RE: How to Reorder/Detect packet loss in case of Payload L2TP
pa ckets?

But the requirement is already there, that either side can insist on
sequence numbers in the data channel.  How is interoperability aided
by allowing some systems to evade requirements that other systems
count on?  I don't consider myself a layering purist, but imho
introducing an l2tp-lite that works only over ipsec would be a mistake.

Barney Wolff

> From: William Dixon <[email-masked]>
> Date: Fri, 14 Apr 2000 15:13:09 -0700
> 
> Don't forget that IPSec mandates sequence numbers as well for both AH &
ESP
> and anti-replay protection on the receiving SA, which uses either a 32 or
64
> packet window (sufficient to detect packet loss, since receiver must
discard
> outside of this window).  So if you want one general mechanism for both
> IPSec tunnels & L2TP/IPSec tunnels to detect packets loss, I'd put it in
> IPSec and have L2TP report it.  I realize this doesn't apply to L2TP clear
> packets, but I'd hate to see interop requirements develop to include L2TP
> sequence numbers just to detect packet loss.

---

From: "W. Mark Townsley" <[email-masked]>
Date: Wed, 19 Apr 2000 12:18:20 -0400

We could certainly *suggest* leaving sequence numbers off on the l2tp
data channel with ipsec, citing the reasons you have stated. This of
course would not be license to leave out support.

---

From: "W. Mark Townsley" <[email-masked]>
Date: Wed, 19 Apr 2000 13:50:55 -0400