IPv6 fragments get partially blocked (CATV DS-lite in Bülach)

Tthlavacek · 2. Sept 2024

UPC

Giga Connect Box

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

Daniele_Sunrise · 2. Sept 2024

thlavacek To check your modem, please send us your customer number, address and date of birth via private message. We will then be happy to check the configuration of your modem.

Greetings
Daniele

Tthlavacek · 4. Sept 2024

Quick update for the record: It was not the modem issue. Based on help and advice from @Daniele_Sunrise I will escalate it to the Sunrise Tech support directly.

Btw. this measurement history actually shows that it is a long-running problem, but it is so well hidden by MSS-clamp that nobody noticed it: https://stats.labs.apnic.net/v6frag/AS6730?a=6730&c=CH&ll=1&ss=thiss&xx=1&w=1&d=1

Daniele_Sunrise · 5. Sept 2024

thlavacek Thank you for the details!

I have just forwarded your findings to our technicians. I will get back to you as soon as I have received feedback.

Greetings
Daniele

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