On 21 Aug 2007, at 22:54, Jun-ichiro itojun Hagino wrote:
IEEE 802 standards do not permit variation in the link MTU for Ethernet. Attempts to persuade IEEE 802 to approve use of jumbo-MTUs (e.g. 9180 bytes + Ethernet framing) have consistently failed within the IEEE 802.ok, then pls think about FDDI-to-ethernet bridge (i guess it is also spec conformant but there are products), and/or 802.11 bridges.
My understanding is that 802.11 has no difference in Link MTU size from 802.3. If someone thinks that is incorrect, citing the specific IEEE standards and the specific section numbers from those standards would be helpful. FDDI chipsets ceased manufacture around 2002, so FDDI has not been available for purchase for several years already. Almost all the FDDI in the world has already been removed by now. (US Navy had been a very large FDDI user and they started work on removing all of their FDDI around 2000/2001.) I think no one has FDDI in their house LAN or small-office LAN anyway; house LAN and SOHO LANwas the focus of my posting. Large company networks will not have difficulty obtaining a prefix shorter than /64 from a commercial ISP that supports IPv6, so those are not an issue either. Token Ring, FDDI, and Token Bus are almost non-existent today in the deployed world -- and never had significant deployment in home LANs or small-office LANs. So it seems the only potential issue with link MTU compatibility in the real world is from Jumbo Ethernet (9180 bytes + Ethernet framing overhead) -- and Jumbo Ethernet is explicitly violating the IEEE 802 standards. (Some very-lost-cost Ethernet switch/hub or router products can support Jumbo Ethernet, but I believe that feature defaults to OFF.) Cheers, Ran rja@xxxxxxxxxxxxxxxxxxx _______________________________________________ Ietf@xxxxxxxx https://www1.ietf.org/mailman/listinfo/ietf