Since about a week or so it's become impossible to reach wp.com content over IPv6.
IPv4 content does work fine, using the IPv6 literal returns a 404 which is small enough to fit in a smaller 1480 byte MTU.
I have another test site that has a clean 1500 byte mtu and I can fetch the s0.wp.com page from there.
It looks like tunneled IPv6 users might be in hurt here.
Yes, a middlebox is discarding PTB messages before they reach the webserver: $ scamper -F ipfw -I "tbit -u 'http://s0.wp.com/' 2606:2800:220:1c85:99b:1b56:207e:ea5" tbit from 2001:48d0:101:501:d267:e5ff:fe14:a701 to 2606:2800:220:1c85:99b:1b56:207e:ea5 server-mss 1440, result: pmtud-fail app: http, url: http://s0.wp.com/ [ 0.048] TX SYN 64 seq = 0:0 [ 0.061] RX SYN/ACK 64 seq = 0:1 [ 0.099] TX 60 seq = 1:1 [ 0.148] TX 228 seq = 1:1(168) [ 0.161] RX 60 seq = 1:169 [ 0.162] RX 1500 seq = 1:169(1440) [ 0.162] RX 1500 seq = 1441:169(1440) [ 0.162] RX 1500 seq = 2881:169(1440) [ 0.162] RX 1500 seq = 4321:169(1440) [ 0.162] RX 1500 seq = 5761:169(1440) [ 0.162] RX 914 seq = 7201:169(854) [ 0.198] TX PTB 1280 mtu = 1280 [ 0.248] TX 60 seq = 169:1 [ 3.173] RX 1500 seq = 1:169(1440) [ 3.173] TX PTB 1280 mtu = 1280 [ 6.044] RX FIN 60 seq = 8055:169 [ 6.044] TX 60 seq = 169:1 [ 9.183] RX 1500 seq = 1:169(1440) [ 9.183] TX PTB 1280 mtu = 1280 [ 21.204] RX 1500 seq = 1:169(1440) [ 21.204] TX PTB 1280 mtu = 1280 [ 45.254] RX 1500 seq = 1:169(1440)