the odhcp6c is suffering from instabiliy in reading the ADVERTISE response from SOLICIT requests.
It is probably the cause of another issue reported here in Apr 2022
I have detected by tcpdump that in spite of the upstream server immediately sending the ADVERTISE response odhcp6c does not read it. Typically after a restart the ADVERTISE is not read until 2-3 SOLICITS have been sent (and been responded to by the server).
It is also occurring after quite a number of SOLICITs or never.
In the mean time Router Advertisements are received and processed without problems
Below is a log displaying the behaviour. I have only modified the odhcp6c by inserting som better logging, not changing the internal logic at all.
I have failed in detecting any reason e.g. other programs listening on the same port.
The platform used is Linux Fedora 36 kernel 5.18.13
"Resource temporary available" means no data received before timeout.
Jul 31 01:31:21 ns4 odhcp6c[704]: Sent SOLICIT message to ff02::1:2 err=0, Success)
Jul 31 01:31:21 ns4 odhcp6c[704]: Receive rounds len=-1 <0, rs= 14801534 < re=14927546
Jul 31 01:33:31 ns4 odhcp6c[704]: Receive cycle sock=4 len=-1 tv=126,12000 err=11,Resource temporarily unavailable
Jul 31 01:33:31 ns4 odhcp6c[704]: Sent SOLICIT message to ff02::1:2 err=0, Success)
Jul 31 01:33:31 ns4 odhcp6c[704]: Receive rounds len=-1 <0, rs= 14931070 < re=15055066
Jul 31 01:35:38 ns4 odhcp6c[704]: Receive cycle sock=4 len=-1 tv=123,996000 err=11,Resource temporarily unavailable
Jul 31 01:35:38 ns4 odhcp6c[704]: Sent SOLICIT message to ff02::1:2 err=0, Success)
Jul 31 01:35:38 ns4 odhcp6c[704]: Receive rounds len=-1 <0, rs= 15058046 < re=15178262
Jul 31 01:37:13 ns4 odhcp6c[704]: Receive cycle sock=4 len=-1 tv=120,216000 err=4,Interrupted system call
Jul 31 01:37:13 ns4 odhcp6c[704]: ra_pr: Receive RA sock=5 len=64 err=0,Success
Jul 31 01:37:13 ns4 odhcp6c[704]: ra_pr: Receive RA sock=5 len=-1 err=11,Resource temporarily unavailable
Jul 31 01:37:14 ns4 odhcp6c[135392]: SCRIPT call /usr/sbin/odhcp6c-update eth0 ra-updated 2
Jul 31 01:37:14 ns4 odhcp6c[135392]: ENTER /usr/sbin/odhcp6c-update eth0 ra-updated 2
Jul 31 01:37:14 ns4 odhcp6c[135392]: DONE /usr/sbin/odhcp6c-update eth0 ra-updated 2 rc=0
Jul 31 01:37:14 ns4 odhcp6c[704]: Receive cycle sock=4 len=-1 tv=24,831000 err=4,Interrupted system call
Jul 31 01:37:38 ns4 odhcp6c[704]: Receive cycle sock=4 len=-1 tv=23,720000 err=11,Resource temporarily unavailable
Jul 31 01:37:38 ns4 odhcp6c[704]: Sent SOLICIT message to ff02::1:2 err=0, Success)
Jul 31 01:37:38 ns4 odhcp6c[704]: Receive rounds len=-1 <0, rs= 15178366 < re=15296806
Jul 31 01:39:40 ns4 odhcp6c[704]: Receive cycle sock=4 len=-1 tv=118,440000 err=11,Resource temporarily unavailable
Jul 31 01:39:40 ns4 odhcp6c[704]: Sent SOLICIT message to ff02::1:2 err=0, Success)
Jul 31 01:39:40 ns4 odhcp6c[704]: Receive rounds len=-1 <0, rs= 15299710 < re=15429430
Jul 31 01:41:51 ns4 odhcp6c[704]: Receive cycle sock=4 len=-1 tv=129,720000 err=11,Resource temporarily unavailable
Jul 31 01:41:51 ns4 odhcp6c[704]: Sent SOLICIT message to ff02::1:2 err=0, Success)
Jul 31 01:41:51 ns4 odhcp6c[704]: Receive rounds len=-1 <0, rs= 15430782 < re=15552666