rtsold: specific cases maybe not send signals to dhcp6c

[wevsty]

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Describe the bug

When the ISP forcibly updates the IPV6 prefix, rtsold does not seem to notify dhcp6c to handle it.

My ISP seems to force a new IPV6 prefix to be released every so often, and the ISP doesn't seem to be keeping to its time agreement with its customers. When a new prefix is released, all machines on the LAN are disconnected. Normally, we would think that rtsold would send a SIGHUP to dhcp6c, and that dhcp6c would receive the notification and resend a DHCPv6 request to update the prefix.

However, this does not seem to be the case in my case. This eventually causes all devices to disconnect from the network for a period of time (about 10 minutes in my case).

The results and system logs of capturing packets when a problem is sent can be found in the: https://github.com/opnsense/dhcp6c/issues/37#issuecomment-2261198621 and https://github.com/opnsense/dhcp6c/issues/37#issuecomment-2295244001

Since rtsold gives limited debug information, if there is a way to get more useful information please let me know and I will try to get more information. And if there are any other suggestions to help diagnose the problem, I'd be more than happy to try them.

Tip: to validate your setup was working with the previous version, use opnsense-revert (https://docs.opnsense.org/manual/opnsense_tools.html#opnsense-revert)

To Reproduce

Waiting for ISPs to issue new IPV6 prefixes

Expected behavior

rtsold should notify dhcp6c within a few seconds so that the disconnection should only take a few seconds.

Describe alternatives you considered

None.

Screenshots

None.

Relevant log files

None.

Additional context

Add any other context about the problem here.

Environment

OPNsense 24.7.1-amd64 Dell Optiplex 3070 MFF Intel(R) Core(TM) i3-8100T CPU @ 3.10GHz (4 cores, 4 threads) Network card: Intel I210 (WAN) Realtek NIC (LAN)