Subject: RE: (ngtrans) I-D ACTION:draft-ietf-ngtrans-mech-v2-01.txt

From: "Dave Thaler" <[email-masked]>
Date: Thu, 14 Nov 2002 17:52:24 -0800

> From: Fred Templin [mailto:[email-masked]]
[...]
> Conclusion - the fixed interface MTU of 1280 bytes suggested in the
> MECH text is too small. I suggest it be changed to 1428 (1500 minus
> 72 for IPv4/VPN encaps).

I'm told by our VPN folks here that the MTU on our IPv4 VPN 
interfaces is 1400.  This was based on overhead for 
IP+AH+ESP+UDP+L2TP+PPP, and still fitting in an Ethernet MTU.

Hence to avoid gratuitous fragmentation, we'd want the MTU
inside an IPv6-over-IPv4 tunnel interface to be at most 1380.

-Dave

---

From: "Fred L. Templin" <[email-masked]>
Date: Fri, 15 Nov 2002 12:16:33 -0800

> inside an IPv6-over-IPv4 tunnel interface to be at most 1380.

Regarding the tunnel MTU, my conclusion was incorrect. Fragmentation
due to improperly-configured tunnel MTUs is a growing problem in the
Internet, thus it is very important that we get this right. Many thanks
to Dave Thaler and his colleagues for the accurate analysis.

Fred Templin
[email-masked]