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



Dave Thaler wrote:
From: Fred Templin [mailto:osprey67@yahoo.com]
[...]

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

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
ftemplin@iprg.nokia.com