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