I've had a look through and I have a few comments. Regarding smallest MTUs, I understand from Geoff Huston that it's common for IPv6 breakage to start at 1281 bytes.
I would find it easier to understand the recommendations if the requirements for responder and requester were separated. In particular I don't know how a responder can do MTU discovery (though a simplified version might be possible). Here's my understanding of your recommendations: Requester: * should have a default EDNS buffer size no more than 1500 bytes (smaller than the 4096 that is currently typical, but bigger than the flag day recommendation) * should probe to discover the real MTU per destination, which can be less than the default, and use the discovered MTU for the EDNS buffer size in queries (resolvers already do this) * at the moment UDP timeouts don't cause fallback to TCP, but this should be added to the list of recovery tactics * requesters are supposed to guess (how?) the size of response before sending a query, so that they can skip UDP and go straight to TCP * should set the DONTFRAG option, though it's unlikely they are sending a query big enough for this to matter. (UPDATE clients need to care, though.) Responder: * should have a default UDP response size limit of no more than 1500 bytes (smaller than the 4096 that is currently typical, but bigger than the flag day recommendation) * should limit response sizes by based on the minimum of the request's EDNS buffer size and the server's limit (servers already do this) * should use minimal responses * should set the DONTFRAG option on responses * should listen for ICMP frag needed packets, and react by re-sending the response (which is embedded in the ICMP packet) with a TC bit set Network: * should send rate-limited ICMP frag needed messages to DNS servers when appropriate Tony. -- f.anthony.n.finch <[email protected]> http://dotat.at/ Mull of Kintyre to Ardnamurchan Point: Southeast 4 to 6, occasionally 7 at first, then veering south 3 to 5 later. Slight or moderate, becoming moderate or rough near Tiree. Rain at times then fair, then showers later. Moderate or good. _______________________________________________ DNSOP mailing list [email protected] https://www.ietf.org/mailman/listinfo/dnsop
