[just discovered in my unsent messages queue from offline composition, probably not timely, but...] Iljitsch van Beijnum wrote:
We can't replace path MTU discovery (but hopefully people will start to realize ICMP messages were invented for another reason than job security for firewalls). But what we need is a way for 10/100 Mbps 1500 byte hosts to live with 1000 Mbps 9000 byte hosts on the same subnet. I thought IPv6 neighbor discovery supported this because ND can communicate the MTU between hosts on the same subnet, but unfortunately this is a subnet-wide MTU and not a per-host MTU, which is what we really need.
A decade ago, when I designed SIPP Neighbor Discovery, it saved per destination "maximum unfragmented datagram size" in the route cache, and each I-Am-Here message Heard specified Maximum Receive Unit (MRU) per host. Thus, once upon a time, IPv6 had what you need. Unfortunately, the IPv6 group stripped out such innovative features. I stopped paying attention after the new editor stated something like "it worked for ethernet, we really don't need any more than that." Well, we used IPv4 from '83, and designed SIPP (cum IPv6) in '93. IPv6 is a failure -- maybe it's time for this decade's design? Or maybe even some of the features some of us thought we needed a decade ago? -- William Allen Simpson Key fingerprint = 17 40 5E 67 15 6F 31 26 DD 0D B9 9B 6A 15 2C 32