Hi, There was quite a bit discussion on IPv6 PMTUD on the v6ops list within the past couple of weeks. Studies have shown that PTB messages can be dropped due to filtering even for ICMPv6. There was also concern for the one (or more) RTTs required for PMTUD to work, and for dealing with bogus PTB messages.
The concerns were explicitly linked to IPv6 tunnels, so I drafted a proposed solution: https://datatracker.ietf.org/doc/draft-generic-v6ops-tunmtu/ In this proposal the tunnel ingress performs the following treatment of packets of various sizes: 1) For IPv6 packets no larger than 1280, admit the packet into the tunnel w/o fragmentation. Assumption is that all IPv6 links have to support a 1280 MinMTU, so the packet will get through. 2) For IPv6 packets larger than 1500, admit the packet into the tunnel w/o fragmentation. Assumption is that the sender would only send a 1501+ packet if it has some way of policing the PMTU on its own, e.g. through the use of RC4821. 3) For IPv6 packets between 1281-1500, break the packet into two (roughly) equal-sized pieces and admit each piece into the tunnel. (In other words, intentionally violate the IPv6 deprecation of router fragmentation.) Assumption is that the final destination can reassemble at least 1500, and that the 32-bit Identification value inserted by the tunnel provides sufficient assurance against reassembly mis-associations. I presume no one here would object to clauses 1) and 2). Clause 3) is obviously a bit more controversial - but, what harm would it cause from an operational standpoint? Thanks - Fred fred.l.temp...@boeing.com
