Templin, Fred L wrote:
I wish you luck in getting your host IP stacks to work properly without ICMP, especially as you deploy IPv6.
From what I've heard, ICMPv6 is already being filtered, including PTBs.
As v6 PTBs are specified to be generated even against multicast packets, it is of course that they are dropped to prevent ICMP implosions. But, it is a very serious problem of not only tunnels but entire IPv6. That is, if PMTUD is unavailable, IPv6 hosts are prohibited to send packets larger than 1280B. Then, ignoring the prohibition, tunnel end points may send packets a little larger than 1280B, which means physical link MTU of 1500B or a little smaller than that is enough for nested tunnels. Thus, no new tunneling protocol is necessary. The harder part of the job is to disable PMTUD on all the IPv6 implementations.
I have also heard that IPv6 fragments are also being dropped unconditionally along some paths.
Again, it is not a problem of tunnels only. If that is the operational reality, specifications on fragmentation must be dropped from IPv6 specification. Masataka Ohta