It would be informative to understand what interface MTU the hosts providing DNS use, in the roots. This is not to suggest there has to be a defined one, but it would help understand how people interact in the UDP/TCP shift under TC=1, because of the lack of ICMP/ICMPv6 signal (ICMP filters) and the effect of the server-side in TCP setting a lower MSS avoiding the problem. Could the caucus act as a channel to get this data? -George