Hi! I noticed that IPv6 fragments (even the short ones) are not passing from some remote (i.e. Frankfurt, London, US) networks back to me. Interestingly I can send fragments outside.
Here is an example (home host is connected over CATV DS-lite in Bülach), target is in a Frankfurt data center (traceroute goes apparently over Tinet and ZenLayer) but I observed the same behavior with many different targets across the globe:
[th@home ~]$ ip addr
...
20: enp6s0f4u1u4u4: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
link/ether 34:d0:b8:c0:b5:34 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.93/24 brd 192.168.1.255 scope global dynamic noprefixroute enp6s0f4u1u4u4
valid_lft 77800sec preferred_lft 77800sec
inet6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6/64 scope global dynamic noprefixroute
valid_lft 1209598sec preferred_lft 604798sec
inet6 fe80::172:7df6:3d7:565b/64 scope link noprefixroute
valid_lft forever preferred_lft forever
[th@home ~]$ ping 2602:fb2b:110:1::a001 -s 1452
PING 2602:fb2b:110:1::a001 (2602:fb2b:110:1::a001) 1452 data bytes
1460 bytes from 2602:fb2b:110:1::a001: icmp_seq=1 ttl=54 time=21.0 ms
1460 bytes from 2602:fb2b:110:1::a001: icmp_seq=2 ttl=54 time=16.6 ms
1460 bytes from 2602:fb2b:110:1::a001: icmp_seq=3 ttl=54 time=16.8 ms
^C
--- 2602:fb2b:110:1::a001 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2001ms
rtt min/avg/max/mdev = 16.559/18.125/20.983/2.023 ms
[th@hroch ~]$ ping 2602:fb2b:110:1::a001 -s 1453
PING 2602:fb2b:110:1::a001 (2602:fb2b:110:1::a001) 1453 data bytes
^C
--- 2602:fb2b:110:1::a001 ping statistics ---
6 packets transmitted, 0 received, 100% packet loss, time 5130ms
root@home:/home/th# tcpdump -i enp6s0f4u1u4u4 -n host 2602:fb2b:110:1::a001 and port ! 22
dropped privs to tcpdump
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on enp6s0f4u1u4u4, link-type EN10MB (Ethernet), snapshot length 262144 bytes
12:13:49.521870 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: ICMP6, echo request, id 127, seq 1, length 1460
12:13:49.542825 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: ICMP6, echo reply, id 127, seq 1, length 1460
12:13:50.522269 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: ICMP6, echo request, id 127, seq 2, length 1460
12:13:50.538785 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: ICMP6, echo reply, id 127, seq 2, length 1460
12:13:51.523356 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: ICMP6, echo request, id 127, seq 3, length 1460
12:13:51.540131 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: ICMP6, echo reply, id 127, seq 3, length 1460
12:13:53.643286 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (0|1448) ICMP6, echo request, id 128, seq 1, length 1448
12:13:53.643310 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (1448|13)
12:13:54.676579 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (0|1448) ICMP6, echo request, id 128, seq 2, length 1448
12:13:54.676609 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (1448|13)
12:13:55.700630 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (0|1448) ICMP6, echo request, id 128, seq 3, length 1448
12:13:55.700658 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (1448|13)
12:13:56.724805 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (0|1448) ICMP6, echo request, id 128, seq 4, length 1448
12:13:56.724835 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (1448|13)
12:13:57.748646 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (0|1448) ICMP6, echo request, id 128, seq 5, length 1448
12:13:57.748677 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (1448|13)
12:13:58.772828 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (0|1448) ICMP6, echo request, id 128, seq 6, length 1448
12:13:58.772878 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (1448|13)
^C
18 packets captured
18 packets received by filter
0 packets dropped by kernel
root@fr1:/home/thlavacek# tcpdump -i enp6s19 -n host 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 and port ! 22
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on enp6s19, link-type EN10MB (Ethernet), snapshot length 262144 bytes
10:13:49.530779 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: ICMP6, echo request, id 127, seq 1, length 1460
10:13:49.530842 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: ICMP6, echo reply, id 127, seq 1, length 1460
10:13:50.528156 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: ICMP6, echo request, id 127, seq 2, length 1460
10:13:50.528214 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: ICMP6, echo reply, id 127, seq 2, length 1460
10:13:51.529777 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: ICMP6, echo request, id 127, seq 3, length 1460
10:13:51.529804 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: ICMP6, echo reply, id 127, seq 3, length 1460
10:13:53.653446 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (0|1448) ICMP6, echo request, id 128, seq 1, length 1448
10:13:53.656702 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (1448|13)
10:13:53.656739 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: frag (0|1448) ICMP6, echo reply, id 128, seq 1, length 1448
10:13:53.656748 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: frag (1448|13)
10:13:54.685428 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (0|1448) ICMP6, echo request, id 128, seq 2, length 1448
10:13:54.688970 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (1448|13)
10:13:54.689029 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: frag (0|1448) ICMP6, echo reply, id 128, seq 2, length 1448
10:13:54.689049 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: frag (1448|13)
10:13:55.709356 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (0|1448) ICMP6, echo request, id 128, seq 3, length 1448
10:13:55.713307 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (1448|13)
10:13:55.713337 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: frag (0|1448) ICMP6, echo reply, id 128, seq 3, length 1448
10:13:55.713346 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: frag (1448|13)
10:13:56.735380 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (0|1448) ICMP6, echo request, id 128, seq 4, length 1448
10:13:56.738622 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (1448|13)
10:13:56.738682 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: frag (0|1448) ICMP6, echo reply, id 128, seq 4, length 1448
10:13:56.738699 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: frag (1448|13)
10:13:57.757374 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (0|1448) ICMP6, echo request, id 128, seq 5, length 1448
10:13:57.762591 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (1448|13)
10:13:57.762651 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: frag (0|1448) ICMP6, echo reply, id 128, seq 5, length 1448
10:13:57.762671 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: frag (1448|13)
10:13:58.779440 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (0|1448) ICMP6, echo request, id 128, seq 6, length 1448
10:13:58.782589 IP6 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 > 2602:fb2b:110:1::a001: frag (1448|13)
10:13:58.782620 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: frag (0|1448) ICMP6, echo reply, id 128, seq 6, length 1448
10:13:58.782628 IP6 2602:fb2b:110:1::a001 > 2a02:aa11:380:300:8039:5fbc:b93a:bbc6: frag (1448|13)
^C
30 packets captured
30 packets received by filter
0 packets dropped by kernel
[th@home ~]$ traceroute 2602:fb2b:110:1::a001
traceroute to 2602:fb2b:110:1::a001 (2602:fb2b:110:1::a001), 30 hops max, 80 byte packets
1 2a02:aa11:380:300::1 (2a02:aa11:380:300::1) 0.936 ms 1.116 ms 1.244 ms
2 2a02:aa04:0:1030::1 (2a02:aa04:0:1030::1) 12.881 ms 23.713 ms 23.720 ms
3 cargos101-bundle-ether1119-1301.v6.aorta.net (2a02:aa00:1:302::1) 19.879 ms 21.590 ms 23.424 ms
4 * * *
5 * * *
6 2001:1700:100::1 (2001:1700:100::1) 23.372 ms 16.299 ms *
7 * * *
8 2001:668:0:2:ffff:0:d5c8:74e1 (2001:668:0:2:ffff:0:d5c8:74e1) 29.327 ms 27.781 ms 29.250 ms
9 2001:668:0:3:ffff:1:0:1ce (2001:668:0:3:ffff:1:0:1ce) 26.357 ms 26.205 ms 27.720 ms
10 2a0b:21c0:1001:14f::2 (2a0b:21c0:1001:14f::2) 35.534 ms 2a0b:21c0:1001:150::2 (2a0b:21c0:1001:150::2) 37.116 ms 2a0b:21c0:1001:14f::2 (2a0b:21c0:1001:14f::2) 37.053 ms
11 2a0b:21c0:1002:15::6 (2a0b:21c0:1002:15::6) 32.455 ms 32.487 ms 2a0b:21c0:1002:15::2 (2a0b:21c0:1002:15::2) 26.470 ms
12 2602:fb2b:110:1::a001 (2602:fb2b:110:1::a001) 22.579 ms 23.979 ms 27.289 ms
root@fr1:/home/thlavacek# traceroute 2a02:aa11:380:300:8039:5fbc:b93a:bbc6
traceroute to 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 (2a02:aa11:380:300:8039:5fbc:b93a:bbc6), 30 hops max, 80 byte packets
1 2602:fb2b:110:1::1001 (2602:fb2b:110:1::1001) 0.711 ms 0.566 ms 0.658 ms
2 2a0b:21c0:1002:15::1 (2a0b:21c0:1002:15::1) 10.797 ms 10.964 ms 11.289 ms
3 2a0b:21c0:1001:15c::1 (2a0b:21c0:1001:15c::1) 1.575 ms 2a0b:21c0:1001:14f::1 (2a0b:21c0:1001:14f::1) 0.386 ms 0.356 ms
4 2404:ff40:1:151::1 (2404:ff40:1:151::1) 0.242 ms 2a0b:21c0:1001:166::1 (2a0b:21c0:1001:166::1) 0.475 ms 2404:ff40:1:151::1 (2404:ff40:1:151::1) 0.205 ms
5 2404:ff40:1:3c::1 (2404:ff40:1:3c::1) 0.378 ms 2404:ff40:1:3d::1 (2404:ff40:1:3d::1) 0.539 ms 2404:ff40:1:3b::1 (2404:ff40:1:3b::1) 0.416 ms
6 2404:ff40:1:38::2 (2404:ff40:1:38::2) 0.534 ms 2404:ff40:1:37::2 (2404:ff40:1:37::2) 0.640 ms 0.609 ms
7 de-fra11b-ri1-ae58-0.v6.aorta.net (2001:730:2d04:a::d52e:b001) 0.549 ms 0.637 ms 0.628 ms
8 de-fra11b-rc1-lo0-0.v6.aorta.net (2001:730:2d00::5474:80d4) 9.637 ms 9.592 ms 9.563 ms
9 ch-zrh03a-rc2-lo0-0.v6.aorta.net (2001:730:2c00::5474:801d) 9.688 ms 9.587 ms 9.417 ms
10 * * *
11 cargos101-lo1.v6.aorta.net (2001:730:2700::5474:faa0) 9.679 ms 9.825 ms 9.883 ms
12 2a02:aa00:1:302::2 (2a02:aa00:1:302::2) 13.789 ms 13.794 ms 13.727 ms
13 2a02:aa04:0:1030:1c61:2328:474b:def7 (2a02:aa04:0:1030:1c61:2328:474b:def7) 20.507 ms 28.361 ms 23.327 ms
14 2a02:aa11:380:300:8039:5fbc:b93a:bbc6 (2a02:aa11:380:300:8039:5fbc:b93a:bbc6) 28.261 ms 28.236 ms 23.050 ms