PMTUD issues with certain CloudFlare hosts (may be region dependent): (destiny:10:21)% wget http://wiki.cyanogenmod.com/w/Main_Page --2015-01-25 10:21:11-- http://wiki.cyanogenmod.com/w/Main_Page Resolving wiki.cyanogenmod.com (wiki.cyanogenmod.com)... 2400:cb00:2048:1::681c:1640, 2400:cb00:2048:1::681c:1740, 104.28.23.64, ... Connecting to wiki.cyanogenmod.com (wiki.cyanogenmod.com)|2400:cb00:2048:1::681c:1640|:80... connected. HTTP request sent, awaiting response... 301 Moved Permanently Location: http://wiki.cyanogenmod.org/w/Main_Page [following] --2015-01-25 10:21:12-- http://wiki.cyanogenmod.org/w/Main_Page Resolving wiki.cyanogenmod.org (wiki.cyanogenmod.org)... 2400:cb00:2048:1::a29f:f568, 2400:cb00:2048:1::a29f:f468, 162.159.244.104, ... Connecting to wiki.cyanogenmod.org (wiki.cyanogenmod.org)|2400:cb00:2048:1::a29f:f568|:80... connected. HTTP request sent, awaiting response... (dax:13:20)% sudo tcpdump -i em0 -ns0 ip6 and net 2400:cb00::/32 Password: tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on em0, link-type EN10MB (Ethernet), capture size 65535 bytes capability mode sandbox enabled 13:21:12.054852 IP6 2001:48c8:1:105:21c:c0ff:feb2:8dbd.44028 > 2400:cb00:2048:1::681c:1640.80: Flags [S], seq 1130519030, win 14400, options [mss 1440,sackOK,TS val 2440917347 ecr 0,nop,wscale 7], length 0 13:21:12.078479 IP6 2400:cb00:2048:1::681c:1640.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.44028: Flags [S.], seq 1220943112, ack 1130519031, win 28800, options [mss 1440,nop,nop,sackOK,nop,wscale 10], length 0 13:21:12.154972 IP6 2001:48c8:1:105:21c:c0ff:feb2:8dbd.44028 > 2400:cb00:2048:1::681c:1640.80: Flags [.], ack 1, win 113, length 0 13:21:12.154999 IP6 2001:48c8:1:105:21c:c0ff:feb2:8dbd.44028 > 2400:cb00:2048:1::681c:1640.80: Flags [P.], seq 1:130, ack 1, win 113, length 129 13:21:12.179439 IP6 2400:cb00:2048:1::681c:1640.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.44028: Flags [.], ack 130, win 30, length 0 13:21:12.313569 IP6 2400:cb00:2048:1::681c:1640.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.44028: Flags [P.], seq 1:678, ack 130, win 30, length 677 13:21:12.313572 IP6 2400:cb00:2048:1::681c:1640.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.44028: Flags [P.], seq 678:683, ack 130, win 30, length 5 13:21:12.391046 IP6 2001:48c8:1:105:21c:c0ff:feb2:8dbd.44028 > 2400:cb00:2048:1::681c:1640.80: Flags [.], ack 678, win 124, length 0 13:21:12.391071 IP6 2001:48c8:1:105:21c:c0ff:feb2:8dbd.44028 > 2400:cb00:2048:1::681c:1640.80: Flags [.], ack 683, win 124, length 0 13:21:12.396902 IP6 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285 > 2400:cb00:2048:1::a29f:f568.80: Flags [S], seq 1608603731, win 14400, options [mss 1440,sackOK,TS val 2440917436 ecr 0,nop,wscale 7], length 0 13:21:12.421060 IP6 2400:cb00:2048:1::a29f:f568.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285: Flags [S.], seq 31775464, ack 1608603732, win 28800, options [mss 1440,nop,nop,sackOK,nop,wscale 10], length 0 13:21:12.499321 IP6 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285 > 2400:cb00:2048:1::a29f:f568.80: Flags [.], ack 1, win 113, length 0 13:21:12.499439 IP6 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285 > 2400:cb00:2048:1::a29f:f568.80: Flags [P.], seq 1:130, ack 1, win 113, length 129 13:21:12.522726 IP6 2400:cb00:2048:1::a29f:f568.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285: Flags [.], ack 130, win 30, length 0 13:21:12.657065 IP6 2400:cb00:2048:1::a29f:f568.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285: Flags [.], seq 1:1441, ack 130, win 30, length 1440 13:21:12.657108 IP6 2001:48c8:1:2::2 > 2400:cb00:2048:1::a29f:f568: ICMP6, packet too big, mtu 1280, length 1240 13:21:12.657188 IP6 2400:cb00:2048:1::a29f:f568.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285: Flags [.], seq 1441:2881, ack 130, win 30, length 1440 13:21:12.657190 IP6 2400:cb00:2048:1::a29f:f568.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285: Flags [.], seq 2881:4321, ack 130, win 30, length 1440 13:21:12.657192 IP6 2400:cb00:2048:1::a29f:f568.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285: Flags [.], seq 4321:5761, ack 130, win 30, length 1440 13:21:12.657194 IP6 2400:cb00:2048:1::a29f:f568.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285: Flags [.], seq 5761:7201, ack 130, win 30, length 1440 13:21:12.657195 IP6 2400:cb00:2048:1::a29f:f568.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285: Flags [P.], seq 7201:8641, ack 130, win 30, length 1440 13:21:12.657196 IP6 2400:cb00:2048:1::a29f:f568.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285: Flags [.], seq 8641:10081, ack 130, win 30, length 1440 13:21:12.657198 IP6 2400:cb00:2048:1::a29f:f568.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285: Flags [.], seq 10081:11521, ack 130, win 30, length 1440 13:21:12.657199 IP6 2400:cb00:2048:1::a29f:f568.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285: Flags [.], seq 11521:12961, ack 130, win 30, length 1440 13:21:12.657202 IP6 2400:cb00:2048:1::a29f:f568.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285: Flags [.], seq 12961:14401, ack 130, win 30, length 1440 13:21:12.657325 IP6 2001:48c8:1:2::2 > 2400:cb00:2048:1::a29f:f568: ICMP6, packet too big, mtu 1280, length 1240 13:21:12.657327 IP6 2001:48c8:1:2::2 > 2400:cb00:2048:1::a29f:f568: ICMP6, packet too big, mtu 1280, length 1240 13:21:12.657328 IP6 2001:48c8:1:2::2 > 2400:cb00:2048:1::a29f:f568: ICMP6, packet too big, mtu 1280, length 1240 13:21:12.657330 IP6 2001:48c8:1:2::2 > 2400:cb00:2048:1::a29f:f568: ICMP6, packet too big, mtu 1280, length 1240 13:21:12.657331 IP6 2001:48c8:1:2::2 > 2400:cb00:2048:1::a29f:f568: ICMP6, packet too big, mtu 1280, length 1240 13:21:12.657333 IP6 2001:48c8:1:2::2 > 2400:cb00:2048:1::a29f:f568: ICMP6, packet too big, mtu 1280, length 1240 13:21:12.657334 IP6 2001:48c8:1:2::2 > 2400:cb00:2048:1::a29f:f568: ICMP6, packet too big, mtu 1280, length 1240 13:21:12.657335 IP6 2001:48c8:1:2::2 > 2400:cb00:2048:1::a29f:f568: ICMP6, packet too big, mtu 1280, length 1240 13:21:12.657337 IP6 2001:48c8:1:2::2 > 2400:cb00:2048:1::a29f:f568: ICMP6, packet too big, mtu 1280, length 1240 13:21:13.153889 IP6 2400:cb00:2048:1::a29f:f568.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285: Flags [.], seq 1:1441, ack 130, win 30, length 1440 13:21:13.153944 IP6 2001:48c8:1:2::2 > 2400:cb00:2048:1::a29f:f568: ICMP6, packet too big, mtu 1280, length 1240 13:21:13.753885 IP6 2400:cb00:2048:1::a29f:f568.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285: Flags [.], seq 1:1441, ack 130, win 30, length 1440 13:21:13.753933 IP6 2001:48c8:1:2::2 > 2400:cb00:2048:1::a29f:f568: ICMP6, packet too big, mtu 1280, length 1240 13:21:14.953890 IP6 2400:cb00:2048:1::a29f:f568.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285: Flags [.], seq 1:1441, ack 130, win 30, length 1440 13:21:14.953944 IP6 2001:48c8:1:2::2 > 2400:cb00:2048:1::a29f:f568: ICMP6, packet too big, mtu 1280, length 1240 13:21:17.353890 IP6 2400:cb00:2048:1::a29f:f568.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285: Flags [.], seq 1:1441, ack 130, win 30, length 1440 13:21:17.353940 IP6 2001:48c8:1:2::2 > 2400:cb00:2048:1::a29f:f568: ICMP6, packet too big, mtu 1280, length 1240 13:21:22.163879 IP6 2400:cb00:2048:1::a29f:f568.80 > 2001:48c8:1:105:21c:c0ff:feb2:8dbd.60285: Flags [.], seq 1:1441, ack 130, win 30, length 1440 13:21:22.163937 IP6 2001:48c8:1:2::2 > 2400:cb00:2048:1::a29f:f568: ICMP6, packet too big, mtu 1280, length 1240 But, from a similar tunnel in a different location (east coast USA vs. west coast USA; differernt AAAAs from CloudFlare), this works fine: (nox:19:35)% wget -O /dev/null http://wiki.cyanogenmod.org/w/Main_Page --2015-01-25 19:35:59-- http://wiki.cyanogenmod.org/w/Main_Page Resolving wiki.cyanogenmod.org (wiki.cyanogenmod.org)... 2400:cb00:2048:1::a29f:f468, 2400:cb00:2048:1::a29f:f568, 162.159.244.104, ... Connecting to wiki.cyanogenmod.org (wiki.cyanogenmod.org)|2400:cb00:2048:1::a29f:f468|:80... connected. HTTP request sent, awaiting response... 200 OK Length: unspecified [text/html] Saving to: ‘/dev/null’ /dev/null [ <=> ] 44.33K --.-KB/s in 0.1s 2015-01-25 19:36:00 (409 KB/s) - ‘/dev/null’ saved [45398]