What's really needed is a service that looks up a given web page over IPv6 from behind a 1280 byte MTU link and reports if all the elements load or not. It dumps a list of elements with success/fail.
This would be useful to send the idiots that block ICMPv6 PTB yet send packets bigger than 1280 bytes out too.
http://www.wand.net.nz/scamper/ Works on MacOS X and FreeBSD. It uses IPFW and rules 1-500 as necessary. Example below, showing a website sending > 1280 but ignoring PTBs sent to it. $ sudo scamper -F ipfw -I "tbit -t pmtud -u 'http://www.sapo.pt/' 2001:8a0:2104:ff:213:13:146:140" tbit from 2001:470:d:4de:21f:3cff:fe20:bf4e to 2001:8a0:2104:ff:213:13:146:140 server-mss 1460, result: pmtud-fail app: http, url: http://www.sapo.pt/ [ 0.048] TX SYN 64 seq = 0:0 [ 0.254] RX SYN/ACK 64 seq = 0:1 [ 0.255] TX 60 seq = 1:1 [ 0.255] TX 230 seq = 1:1(170) [ 0.450] RX 60 seq = 1:171 [ 0.469] RX 1460 seq = 1:171(1400) [ 0.469] TX PTB 1280 mtu = 1280 [ 0.470] RX 1460 seq = 1401:171(1400) [ 3.467] RX 1460 seq = 1:171(1400) [ 3.467] TX PTB 1280 mtu = 1280 [ 9.468] RX 1460 seq = 1:171(1400) [ 9.468] TX PTB 1280 mtu = 1280 [ 21.471] RX 1460 seq = 1:171(1400) [ 21.471] TX PTB 1280 mtu = 1280 [ 31.933] RX RST 60 seq = 1:4294923802