[solved] Router cannot ping some local IPV6 addresses

CharlesJC · April 29, 2020, 6:08pm

When I ping a known local IPV6 address from the router, it sometimes fails. However, when I ping the same address from a different machine on my network, it is available. There's hints that it's not consistent over time, but I'll have to monitor again in the morning to prove that.

I'm running OpenWRT 19.07.02 on a TP-Link Archer C2600. What diagnostics should I run to isolate this issue? Are there any logs that I should review?

I did go through the system log from luci, however spotted nothing of interest. I'm comfortable with command line but far from an expert, so my starting point is usually luci.

To prove this issue, I gathered a list of local IPV6 addresses from various machines on my network using
ip -f inet6 neigh

or equivalents on other linux distros. Then compiled and sorted these addresses into a list of
ping -c 1 x

commands, and ran the same script both on the router and on another machine. Finally processed the output results to demonstrate the issue

The results from the router

fe80::211:32ff:fe26:f0c5        1 packets received, 0% packet loss
fe80::215:5dff:fe01:aa0b        1 packets received, 0% packet loss
**fe80::215:5dff:fe01:aa0c        0 packets received, 100% packet loss**
fe80::215:5dff:fe01:aa0f        1 packets received, 0% packet loss
fe80::62e3:27ff:fec8:4a10       1 packets received, 0% packet loss
fe80::94c9:2915:3b6:b3e1        1 packets received, 0% packet loss
fe80::9c03:f49d:9a2:ce05        1 packets received, 0% packet loss
fe80::cb3:edb1:cace:4385        1 packets received, 0% packet loss
fda6:w:x::1     1 packets received, 0% packet loss
**fda6:w:x::2     0 packets received, 100% packet loss**
**fda6:w:x::8888:8888     0 packets received, 100% packet loss**
**fda6:w:x::aaaa:aaaa     0 packets received, 100% packet loss**
fda6:w:x::bbbb:bbbb     1 packets received, 0% packet loss
fda6:w:x::ffff:253      1 packets received, 0% packet loss
**fda6:w:x:0:211:32ff:fe26:f0c5   0 packets received, 100% packet loss**
**fda6:w:x:0:215:5dff:fe01:aa0b   0 packets received, 100% packet loss**
**fda6:w:x:0:215:5dff:fe01:aa0f   0 packets received, 100% packet loss**
fda6:w:x:0:6093:cc1c:a761:406a  1 packets received, 0% packet loss
fda6:w:x:0:94c9:2915:3b6:b3e1   0 packets received, 100% packet loss
fda6:w:x:0:bebb:d81a:e585:ecad  1 packets received, 0% packet loss
**2401:y:z:3861::8888:8888        0 packets received, 100% packet loss**
**2401:y:z:3861::aaaa:aaaa        0 packets received, 100% packet loss**
2401:y:z:3861::bbbb:bbbb        1 packets received, 0% packet loss
**2401:y:z:3861::ffff:253 0 packets received, 100% packet loss**
**2401:y:z:3861:211:32ff:fe26:f0c5        0 packets received, 100% packet loss**
**2401:y:z:3861:215:5dff:fe01:aa0b        0 packets received, 100% packet loss**
**2401:y:z:3861:215:5dff:fe01:aa0f        0 packets received, 100% packet loss**
2401:y:z:3861:6093:cc1c:a761:406a       1 packets received, 0% packet loss
**2401:y:z:3861:94c9:2915:3b6:b3e1        0 packets received, 100% packet loss**
2401:y:z:3861:cfd:33c8:d82:e383 1 packets received, 0% packet loss
2401:y:z:3861:e229:9706:6bbc:e7b5       1 packets received, 0% packet loss

And from another machine, all addresses are pingable

fe80::211:32ff:fe26:f0c5        1 received, 0% packet loss
fe80::215:5dff:fe01:aa0b        1 received, 0% packet loss
**fe80::215:5dff:fe01:aa0c        1 received, 0% packet loss**
fe80::215:5dff:fe01:aa0f        1 received, 0% packet loss
fe80::62e3:27ff:fec8:4a10       1 received, 0% packet loss
fe80::94c9:2915:3b6:b3e1        1 received, 0% packet loss
fe80::9c03:f49d:9a2:ce05        1 received, 0% packet loss
fe80::cb3:edb1:cace:4385        1 received, 0% packet loss
fda6:w:x::1     1 received, 0% packet loss
**fda6:w:x::2     1 received, 0% packet loss**
**fda6:w:x::8888:8888     1 received, 0% packet loss**
**fda6:w:x::aaaa:aaaa     1 received, 0% packet loss**
fda6:w:x::bbbb:bbbb     1 received, 0% packet loss
fda6:w:x::ffff:253      1 received, 0% packet loss
**fda6:w:x:0:211:32ff:fe26:f0c5   1 received, 0% packet loss**
**fda6:w:x:0:215:5dff:fe01:aa0b   1 received, 0% packet loss**
**fda6:w:x:0:215:5dff:fe01:aa0f   1 received, 0% packet loss**
fda6:w:x:0:6093:cc1c:a761:406a  1 received, 0% packet loss
fda6:w:x:0:94c9:2915:3b6:b3e1   1 received, 0% packet loss
fda6:w:x:0:bebb:d81a:e585:ecad  1 received, 0% packet loss
**2401:y:z:3861::8888:8888        1 received, 0% packet loss**
**2401:y:z:3861::aaaa:aaaa        1 received, 0% packet loss**
2401:y:z:3861::bbbb:bbbb        1 received, 0% packet loss
**2401:y:z:3861::ffff:253 1 received, 0% packet loss**
**2401:y:z:3861:211:32ff:fe26:f0c5        1 received, 0% packet loss**
**2401:y:z:3861:215:5dff:fe01:aa0b        1 received, 0% packet loss**
**2401:y:z:3861:215:5dff:fe01:aa0f        1 received, 0% packet loss**
2401:y:z:3861:6093:cc1c:a761:406a       1 received, 0% packet loss
**2401:y:z:3861:94c9:2915:3b6:b3e1        1 received, 0% packet loss**
2401:y:z:3861:cfd:33c8:d82:e383 1 received, 0% packet loss
2401:y:z:3861:e229:9706:6bbc:e7b5       1 received, 0% packet loss

trendy · April 29, 2020, 10:50pm

Run a tcpdump on the router:
tcpdump -i br-lan icmp6
Change the eth0 to the physical interface of your lan interface, if it is not the default.
Then from another terminal ping the host. Stop the tcpdump with Ctrl-c and post here the results.

CharlesJC · April 30, 2020, 1:43am

Here's the output. I left it run a while after I stopped the ping to see if there are more interesting packets.
Regarding the names router.lan and dc1.chas.home, I have a conditional forwarder set up for my windows AD DC domain.

tcpdump -i eth1 icmp6
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth1, link-type EN10MB (Ethernet), capture size 262144 bytes
09:20:55.605241 IP6 dc1.chas.home > router.lan: ICMP6, echo request, seq 1, length 64
09:20:55.605483 IP6 router.lan > dc1.chas.home: ICMP6, echo reply, seq 1, length 64
09:20:56.607018 IP6 dc1.chas.home > router.lan: ICMP6, echo request, seq 2, length 64
09:20:56.607226 IP6 router.lan > dc1.chas.home: ICMP6, echo reply, seq 2, length 64
09:20:57.608721 IP6 dc1.chas.home > router.lan: ICMP6, echo request, seq 3, length 64
09:20:57.608920 IP6 router.lan > dc1.chas.home: ICMP6, echo reply, seq 3, length 64
09:20:58.610427 IP6 dc1.chas.home > router.lan: ICMP6, echo request, seq 4, length 64
09:20:58.610635 IP6 router.lan > dc1.chas.home: ICMP6, echo reply, seq 4, length 64
09:20:59.612399 IP6 dc1.chas.home > router.lan: ICMP6, echo request, seq 5, length 64
09:20:59.612605 IP6 router.lan > dc1.chas.home: ICMP6, echo reply, seq 5, length 64
09:21:00.612311 IP6 router.lan > dc1.chas.home: ICMP6, neighbor solicitation, who has dc1.chas.home, length 32
09:21:00.613513 IP6 dc1.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is dc1.chas.home, length 24
09:21:03.502331 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:21:03.502741 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:21:05.738644 IP6 fe80::215:5dff:fe01:aa0f > router.lan: ICMP6, neighbor solicitation, who has router.lan, length 32
09:21:05.738851 IP6 router.lan > fe80::215:5dff:fe01:aa0f: ICMP6, neighbor advertisement, tgt is router.lan, length 24
09:21:07.661998 IP6 fe80::1c6c:3fd4:7860:d935 > fe80::83a:1f4b:c665:cab8: ICMP6, neighbor solicitation, who has fe80::83a:1f4b:c665:cab8, length 32
09:21:07.681170 IP6 fe80::83a:1f4b:c665:cab8 > fe80::1c6c:3fd4:7860:d935: ICMP6, neighbor advertisement, tgt is fe80::83a:1f4b:c665:cab8, length 24
09:21:10.772855 IP6 router.lan > fe80::215:5dff:fe01:aa0f: ICMP6, neighbor solicitation, who has fe80::215:5dff:fe01:aa0f, length 32
09:21:10.773961 IP6 fe80::215:5dff:fe01:aa0f > router.lan: ICMP6, neighbor advertisement, tgt is fe80::215:5dff:fe01:aa0f, length 24
09:21:11.516925 IP6 fe80::83a:1f4b:c665:cab8 > fe80::1c6c:3fd4:7860:d935: ICMP6, neighbor solicitation, who has fe80::1c6c:3fd4:7860:d935, length 32
09:21:11.517769 IP6 fe80::1c6c:3fd4:7860:d935 > fe80::83a:1f4b:c665:cab8: ICMP6, neighbor advertisement, tgt is fe80::1c6c:3fd4:7860:d935, length 24
09:21:43.892244 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:21:43.892639 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:21:48.004696 IP6 fe80::83a:1f4b:c665:cab8 > fe80::1c6c:3fd4:7860:d935: ICMP6, neighbor solicitation, who has fe80::1c6c:3fd4:7860:d935, length 32
09:21:48.005654 IP6 fe80::1c6c:3fd4:7860:d935 > fe80::83a:1f4b:c665:cab8: ICMP6, neighbor advertisement, tgt is fe80::1c6c:3fd4:7860:d935, length 24
09:21:48.506835 IP6 :: > ff02::1:ff00:10: ICMP6, neighbor solicitation, who has ATV.chas.home, length 32
09:21:49.183459 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 32
09:21:49.183478 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 32
09:21:50.185384 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 32
09:21:50.185394 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 32
09:21:51.186517 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 32
09:21:51.186536 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 32
09:21:53.342940 IP6 router.lan > ip6-allnodes: ICMP6, router advertisement, length 176
09:21:53.343935 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is 2401:7400:c802:3861:e229:9706:6bbc:e7b5, length 32
09:21:53.343949 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is fda6:3ce8:c11:0:bebb:d81a:e585:ecad, length 32
09:21:53.572306 IP6 router.lan > fe80::1c6c:3fd4:7860:d935: ICMP6, neighbor solicitation, who has fe80::1c6c:3fd4:7860:d935, length 32
09:21:53.573215 IP6 fe80::1c6c:3fd4:7860:d935 > router.lan: ICMP6, neighbor advertisement, tgt is fe80::1c6c:3fd4:7860:d935, length 24
09:21:54.212581 IP6 router.lan > fe80::9c03:f49d:9a2:ce05: ICMP6, neighbor solicitation, who has fe80::9c03:f49d:9a2:ce05, length 32
09:21:54.212979 IP6 fe80::9c03:f49d:9a2:ce05 > router.lan: ICMP6, neighbor advertisement, tgt is fe80::9c03:f49d:9a2:ce05, length 24
09:21:54.345401 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is 2401:7400:c802:3861:e229:9706:6bbc:e7b5, length 32
09:21:54.345422 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is fda6:3ce8:c11:0:bebb:d81a:e585:ecad, length 32
09:21:55.346515 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is 2401:7400:c802:3861:e229:9706:6bbc:e7b5, length 32
09:21:55.346532 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is fda6:3ce8:c11:0:bebb:d81a:e585:ecad, length 32
09:21:56.290170 IP6 fe80::1c6c:3fd4:7860:d935 > fe80::83a:1f4b:c665:cab8: ICMP6, neighbor solicitation, who has fe80::83a:1f4b:c665:cab8, length 32
09:21:56.292228 IP6 fe80::83a:1f4b:c665:cab8 > fe80::1c6c:3fd4:7860:d935: ICMP6, neighbor advertisement, tgt is fe80::83a:1f4b:c665:cab8, length 24
09:21:58.312524 IP6 fe80::1c6c:3fd4:7860:d935 > router.lan: ICMP6, neighbor solicitation, who has router.lan, length 32
09:21:58.312696 IP6 router.lan > fe80::1c6c:3fd4:7860:d935: ICMP6, neighbor advertisement, tgt is router.lan, length 24
09:22:24.212424 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:22:24.213050 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:22:43.902316 IP6 router.lan > fe80::211:32ff:fe26:f0c5: ICMP6, neighbor solicitation, who has fe80::211:32ff:fe26:f0c5, length 32
09:22:43.902727 IP6 fe80::211:32ff:fe26:f0c5 > router.lan: ICMP6, neighbor advertisement, tgt is fe80::211:32ff:fe26:f0c5, length 24
09:22:48.916665 IP6 fe80::211:32ff:fe26:f0c5 > router.lan: ICMP6, neighbor solicitation, who has router.lan, length 32
09:22:48.916824 IP6 router.lan > fe80::211:32ff:fe26:f0c5: ICMP6, neighbor advertisement, tgt is router.lan, length 24
09:23:04.613089 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:23:04.613508 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:23:45.012815 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:23:45.013289 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:24:25.414279 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:24:25.414773 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:25:05.812555 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:25:05.813082 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:25:11.334457 IP6 router.lan > fe80::215:5dff:fe01:aa0f: ICMP6, neighbor solicitation, who has fe80::215:5dff:fe01:aa0f, length 32
09:25:11.335450 IP6 fe80::215:5dff:fe01:aa0f > router.lan: ICMP6, neighbor advertisement, tgt is fe80::215:5dff:fe01:aa0f, length 24
09:25:16.362528 IP6 fe80::215:5dff:fe01:aa0f > router.lan: ICMP6, neighbor solicitation, who has router.lan, length 32
09:25:16.362752 IP6 router.lan > fe80::215:5dff:fe01:aa0f: ICMP6, neighbor advertisement, tgt is router.lan, length 24
09:25:46.052311 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:25:46.052798 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:25:58.638324 IP6 fe80::211:32ff:fe26:f0c5 > router.lan: ICMP6, neighbor solicitation, who has router.lan, length 32
09:25:58.638542 IP6 router.lan > fe80::211:32ff:fe26:f0c5: ICMP6, neighbor advertisement, tgt is router.lan, length 24
09:26:02.852247 IP6 router.lan > fe80::215:5dff:fe01:aa0b: ICMP6, neighbor solicitation, who has fe80::215:5dff:fe01:aa0b, length 32
09:26:02.853207 IP6 fe80::215:5dff:fe01:aa0b > router.lan: ICMP6, neighbor advertisement, tgt is fe80::215:5dff:fe01:aa0b, length 24
09:26:03.653193 IP6 router.lan > fe80::211:32ff:fe26:f0c5: ICMP6, neighbor solicitation, who has fe80::211:32ff:fe26:f0c5, length 32
09:26:03.653636 IP6 fe80::211:32ff:fe26:f0c5 > router.lan: ICMP6, neighbor advertisement, tgt is fe80::211:32ff:fe26:f0c5, length 24
09:26:07.865450 IP6 fe80::215:5dff:fe01:aa0b > router.lan: ICMP6, neighbor solicitation, who has router.lan, length 32
09:26:07.865645 IP6 router.lan > fe80::215:5dff:fe01:aa0b: ICMP6, neighbor advertisement, tgt is router.lan, length 24
09:26:26.452338 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:26:26.452779 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:26:39.144793 IP6 fe80::1c6c:3fd4:7860:d935 > fe80::83a:1f4b:c665:cab8: ICMP6, neighbor solicitation, who has fe80::83a:1f4b:c665:cab8, length 32
09:26:39.395819 IP6 fe80::83a:1f4b:c665:cab8 > fe80::1c6c:3fd4:7860:d935: ICMP6, neighbor advertisement, tgt is fe80::83a:1f4b:c665:cab8, length 24
09:26:45.183013 IP6 fe80::83a:1f4b:c665:cab8 > fe80::1c6c:3fd4:7860:d935: ICMP6, neighbor solicitation, who has fe80::1c6c:3fd4:7860:d935, length 32
09:26:45.184013 IP6 fe80::1c6c:3fd4:7860:d935 > fe80::83a:1f4b:c665:cab8: ICMP6, neighbor advertisement, tgt is fe80::1c6c:3fd4:7860:d935, length 24
09:27:06.772697 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:27:06.773115 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:27:47.093077 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:27:47.093478 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:28:44.883263 IP6 router.lan > ip6-allnodes: ICMP6, router advertisement, length 176
09:28:44.884264 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is 2401:7400:c802:3861:e229:9706:6bbc:e7b5, length 32
09:28:44.884283 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is fda6:3ce8:c11:0:bebb:d81a:e585:ecad, length 32
09:28:45.885670 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is 2401:7400:c802:3861:e229:9706:6bbc:e7b5, length 32
09:28:45.885689 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is fda6:3ce8:c11:0:bebb:d81a:e585:ecad, length 32
09:28:46.533364 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:28:46.533772 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:28:46.886835 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is 2401:7400:c802:3861:e229:9706:6bbc:e7b5, length 32
09:28:46.886854 IP6 fe80::9c03:f49d:9a2:ce05 > ip6-allnodes: ICMP6, neighbor advertisement, tgt is fda6:3ce8:c11:0:bebb:d81a:e585:ecad, length 32
09:28:58.488359 IP6 fe80::211:32ff:fe26:f0c5 > router.lan: ICMP6, neighbor solicitation, who has router.lan, length 32
09:28:58.488536 IP6 router.lan > fe80::211:32ff:fe26:f0c5: ICMP6, neighbor advertisement, tgt is router.lan, length 24
09:29:03.493562 IP6 router.lan > fe80::211:32ff:fe26:f0c5: ICMP6, neighbor solicitation, who has fe80::211:32ff:fe26:f0c5, length 32
09:29:03.494016 IP6 fe80::211:32ff:fe26:f0c5 > router.lan: ICMP6, neighbor advertisement, tgt is fe80::211:32ff:fe26:f0c5, length 24
09:29:48.132295 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:29:48.132709 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:30:48.612810 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:30:48.613235 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:31:05.422133 IP6 fe80::1c6c:3fd4:7860:d935 > fe80::83a:1f4b:c665:cab8: ICMP6, neighbor solicitation, who has fe80::83a:1f4b:c665:cab8, length 32
09:31:05.663193 IP6 fe80::83a:1f4b:c665:cab8 > fe80::1c6c:3fd4:7860:d935: ICMP6, neighbor advertisement, tgt is fe80::83a:1f4b:c665:cab8, length 24
09:31:50.132283 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:31:50.132720 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:31:55.122359 IP6 fe80::1c6c:3fd4:7860:d935 > fe80::83a:1f4b:c665:cab8: ICMP6, neighbor solicitation, who has fe80::83a:1f4b:c665:cab8, length 32
09:31:56.133531 IP6 fe80::1c6c:3fd4:7860:d935 > fe80::83a:1f4b:c665:cab8: ICMP6, neighbor solicitation, who has fe80::83a:1f4b:c665:cab8, length 32
09:31:57.144626 IP6 fe80::1c6c:3fd4:7860:d935 > fe80::83a:1f4b:c665:cab8: ICMP6, neighbor solicitation, who has fe80::83a:1f4b:c665:cab8, length 32
09:31:58.338452 IP6 fe80::211:32ff:fe26:f0c5 > router.lan: ICMP6, neighbor solicitation, who has router.lan, length 32
09:31:58.338687 IP6 router.lan > fe80::211:32ff:fe26:f0c5: ICMP6, neighbor advertisement, tgt is router.lan, length 24
09:31:59.355294 IP6 fe80::83a:1f4b:c665:cab8 > fe80::1c6c:3fd4:7860:d935: ICMP6, neighbor advertisement, tgt is fe80::83a:1f4b:c665:cab8, length 32
09:31:59.355357 IP6 fe80::83a:1f4b:c665:cab8 > fe80::1c6c:3fd4:7860:d935: ICMP6, neighbor advertisement, tgt is fe80::83a:1f4b:c665:cab8, length 32
09:31:59.355998 IP6 fe80::83a:1f4b:c665:cab8 > fe80::1c6c:3fd4:7860:d935: ICMP6, neighbor advertisement, tgt is fe80::83a:1f4b:c665:cab8, length 32
09:32:03.412904 IP6 router.lan > fe80::211:32ff:fe26:f0c5: ICMP6, neighbor solicitation, who has fe80::211:32ff:fe26:f0c5, length 32
09:32:03.413339 IP6 fe80::211:32ff:fe26:f0c5 > router.lan: ICMP6, neighbor advertisement, tgt is fe80::211:32ff:fe26:f0c5, length 24
09:32:50.692419 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:32:50.692822 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:33:51.332347 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:33:51.332770 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:34:51.812737 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:34:51.813193 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:34:58.332530 IP6 fe80::211:32ff:fe26:f0c5 > router.lan: ICMP6, neighbor solicitation, who has router.lan, length 32
09:34:58.332722 IP6 router.lan > fe80::211:32ff:fe26:f0c5: ICMP6, neighbor advertisement, tgt is router.lan, length 24
09:35:03.412468 IP6 router.lan > fe80::211:32ff:fe26:f0c5: ICMP6, neighbor solicitation, who has fe80::211:32ff:fe26:f0c5, length 32
09:35:03.412881 IP6 fe80::211:32ff:fe26:f0c5 > router.lan: ICMP6, neighbor advertisement, tgt is fe80::211:32ff:fe26:f0c5, length 24
09:35:35.318868 IP6 fe80::1c6c:3fd4:7860:d935 > ff02::1:ff65:cab8: ICMP6, neighbor solicitation, who has fe80::83a:1f4b:c665:cab8, length 32
09:35:35.324635 IP6 fe80::83a:1f4b:c665:cab8 > fe80::1c6c:3fd4:7860:d935: ICMP6, neighbor advertisement, tgt is fe80::83a:1f4b:c665:cab8, length 32
09:35:52.373371 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:35:52.373793 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:36:04.520855 IP6 fe80::83a:1f4b:c665:cab8 > fe80::1c6c:3fd4:7860:d935: ICMP6, neighbor solicitation, who has fe80::1c6c:3fd4:7860:d935, length 32
09:36:04.521800 IP6 fe80::1c6c:3fd4:7860:d935 > fe80::83a:1f4b:c665:cab8: ICMP6, neighbor advertisement, tgt is fe80::1c6c:3fd4:7860:d935, length 24
09:36:46.515767 IP6 :: > ff02::1:ff00:10: ICMP6, neighbor solicitation, who has ATV.chas.home, length 32
09:36:51.572885 IP6 router.lan > fe80::1c6c:3fd4:7860:d935: ICMP6, neighbor solicitation, who has fe80::1c6c:3fd4:7860:d935, length 32
09:36:51.573946 IP6 fe80::1c6c:3fd4:7860:d935 > router.lan: ICMP6, neighbor advertisement, tgt is fe80::1c6c:3fd4:7860:d935, length 24
09:36:52.852495 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
09:36:52.852921 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24
09:36:56.629342 IP6 fe80::1c6c:3fd4:7860:d935 > router.lan: ICMP6, neighbor solicitation, who has router.lan, length 32
09:36:56.629471 IP6 router.lan > fe80::1c6c:3fd4:7860:d935: ICMP6, neighbor advertisement, tgt is router.lan, length 24
09:36:58.651555 IP6 fe80::1c6c:3fd4:7860:d935 > fe80::83a:1f4b:c665:cab8: ICMP6, neighbor solicitation, who has fe80::83a:1f4b:c665:cab8, length 32

CharlesJC · April 30, 2020, 2:26am

I tried an experiment that may show the issue directly. I ran tcpdump in the background then pinged a host that showed packet loss, then from that host pinged the router

root@router:~# tcpdump -i br-lan icmp6 &
root@router:~# tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on br-lan, link-type EN10MB (Ethernet), capture size 262144 bytes
root@router:~# ping -c 2 fda6:3ce8:c11::2
PING fda6:3ce8:c11::2 (fda6:3ce8:c11::2): 56 data bytes
10:19:08.956814 IP6 router.lan > ff02::1:ff00:2: ICMP6, neighbor solicitation, who has fda6:3ce8:c11::2, length 32
10:19:09.972191 IP6 router.lan > ff02::1:ff00:2: ICMP6, neighbor solicitation, who has fda6:3ce8:c11::2, length 32
10:19:11.012958 IP6 router.lan > ff02::1:ff00:2: ICMP6, neighbor solicitation, who has fda6:3ce8:c11::2, length 32
10:19:19.013967 IP6 router.lan > S2.chas.home: ICMP6, neighbor solicitation, who has S2.chas.home, length 32
10:19:19.014378 IP6 S2.chas.home > router.lan: ICMP6, neighbor advertisement, tgt is S2.chas.home, length 24

--- fda6:3ce8:c11::2 ping statistics ---
2 packets transmitted, 0 packets received, 100% packet loss
10:19:20.704341 IP6 fda6:3ce8:c11:0:6093:cc1c:a761:406a > router.lan: ICMP6, echo request, seq 23, length 40
10:19:20.704574 IP6 router.lan > ff02::1:ff61:406a: ICMP6, neighbor solicitation, who has fda6:3ce8:c11:0:6093:cc1c:a761:406a, length 32
10:19:21.732824 IP6 router.lan > ff02::1:ff61:406a: ICMP6, neighbor solicitation, who has fda6:3ce8:c11:0:6093:cc1c:a761:406a, length 32
10:19:22.773000 IP6 router.lan > ff02::1:ff61:406a: ICMP6, neighbor solicitation, who has fda6:3ce8:c11:0:6093:cc1c:a761:406a, length 32
10:19:25.381371 IP6 fda6:3ce8:c11:0:6093:cc1c:a761:406a > router.lan: ICMP6, neighbor solicitation, who has router.lan, length 32
10:19:25.381642 IP6 router.lan > fda6:3ce8:c11:0:6093:cc1c:a761:406a: ICMP6, neighbor advertisement, tgt is router.lan, length 24
10:19:25.397454 IP6 fda6:3ce8:c11:0:6093:cc1c:a761:406a > router.lan: ICMP6, echo request, seq 24, length 40
10:19:25.397670 IP6 router.lan > fda6:3ce8:c11:0:6093:cc1c:a761:406a: ICMP6, echo reply, seq 24, length 40
10:19:26.413398 IP6 fda6:3ce8:c11:0:6093:cc1c:a761:406a > router.lan: ICMP6, echo request, seq 25, length 40
10:19:26.413515 IP6 router.lan > fda6:3ce8:c11:0:6093:cc1c:a761:406a: ICMP6, echo reply, seq 25, length 40
10:19:27.429639 IP6 fda6:3ce8:c11:0:6093:cc1c:a761:406a > router.lan: ICMP6, echo request, seq 26, length 40
10:19:27.429862 IP6 router.lan > fda6:3ce8:c11:0:6093:cc1c:a761:406a: ICMP6, echo reply, seq 26, length 40
10:19:30.452544 IP6 router.lan > fda6:3ce8:c11:0:6093:cc1c:a761:406a: ICMP6, neighbor solicitation, who has fda6:3ce8:c11:0:6093:cc1c:a761:406a, length 32
10:19:30.453409 IP6 fda6:3ce8:c11:0:6093:cc1c:a761:406a > router.lan: ICMP6, neighbor advertisement, tgt is fda6:3ce8:c11:0:6093:cc1c:a761:406a, length 32
10:19:53.715496 IP6 router.lan > ff02::1:ffaa:aaaa: ICMP6, neighbor solicitation, who has S1.chas.home, length 32
l10:19:54.772332 IP6 router.lan > ff02::1:ffaa:aaaa: ICMP6, neighbor solicitation, who has S1.chas.home, length 32
10:19:55.812265 IP6 router.lan > ff02::1:ffaa:aaaa: ICMP6, neighbor solicitation, who has S1.chas.home, length 32
ps10:19:58.530712 IP6 fe80::211:32ff:fe26:f0c5 > router.lan: ICMP6, neighbor solicitation, who has router.lan, length 32
10:19:58.530900 IP6 router.lan > fe80::211:32ff:fe26:f0c5: ICMP6, neighbor advertisement, tgt is router.lan, length 24
10:20:00.723564 IP6 router.lan > ff02::1:ffaa:aaaa: ICMP6, neighbor solicitation, who has S1.chas.home, length 32
10:20:01.732286 IP6 router.lan > ff02::1:ffaa:aaaa: ICMP6, neighbor solicitation, who has S1.chas.home, length 32
10:20:02.772325 IP6 router.lan > ff02::1:ffaa:aaaa: ICMP6, neighbor solicitation, who has S1.chas.home, length 32
10:20:03.572718 IP6 router.lan > fe80::211:32ff:fe26:f0c5: ICMP6, neighbor solicitation, who has fe80::211:32ff:fe26:f0c5, length 32
10:20:03.573168 IP6 fe80::211:32ff:fe26:f0c5 > router.lan: ICMP6, neighbor advertisement, tgt is fe80::211:32ff:fe26:f0c5, length 24

29 packets captured
29 packets received by filter
0 packets dropped by kernel
68 packets dropped by interface

trendy · April 30, 2020, 9:29am

Why not open a second terminal?

From the first capture I don't see any issue. Host replied immediately.
In the second one the router sends 3 neighbor solicitations, but doesn't get any reply. You need to verify why the host is not responding to the solicitations with an advertisement.

CharlesJC · April 30, 2020, 9:53am

because I wanted to demonstrate the issue and show it interleaved? I'll keep it separate next time

The issue that I'm facing is that, from the router, pinging these IPV6 hosts does not work.
However, from the other hosts, pinging each other on these IPV6 addresses does work

These appear to be the failed pings.
I'm not sure why there are 3 when I requested a count of 2 - maybe there's an additional routing discovery prior to the actual pings?

trendy · April 30, 2020, 10:53am

It is mixed and hard to read, better keep separate terminals.

These are not pings, these are neighbor solicitations, the equivalent of arp-who-has in IPv4.

dlakelan · April 30, 2020, 2:36pm

@CharlesJC, exactly, the router is trying to find out which MAC address is associated to the ipv6 address, but is not getting a reply. therefore it can't send the ping, since it doesn't know what MAC to send it to.

try tcp dump on the other machine. does it see the neighbor solicitations? does it send replies?

on this network do you have fancy managed switches? sometimes these have neighbor discovery filtering...

CharlesJC · April 30, 2020, 4:10pm

Yes, though hardly fancy. A quick google search for the switch model and icmpv6 quickly indicates that I must turn off IGMP snooping. As soon as I did that, everying else started to work.

Thank-you @dlakelan and @trendy for your help. I learned quite a bit on the way.

dlakelan · April 30, 2020, 4:12pm

incidentally, which switch model is it?

CharlesJC · April 30, 2020, 4:14pm

TP-Link TL-SG108PE

dlakelan · April 30, 2020, 4:15pm

Hmm.. I have several of those on my network, with IGMP snooping, and haven't had issues. However I immediately first thing out of the box update the firmware on them. You might try the same.

CharlesJC · April 30, 2020, 4:17pm

Exactly. Did that when I first got it.

dlakelan · April 30, 2020, 4:42pm

Well, for me it hasn't been an issue, but I have one additional switch the GS1900-24e from zyxel, and I believe it's the IGMP querier, so it might be that some function you are seeing be problematic is bypassed in my network.

tmomas · May 10, 2020, 4:42pm

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