Arch Linux

mcloaked

Member

From: Yorkshire, UK

Registered: 2012-02-02

Posts: 1,360

[SOLVED]ip6 ping/ssh between two machines with ULA fails after updates

I have machines on my LAN which have ipv6 including each machine with a ULA that has worked without problems, including WAN ipv6, for some years.  After recent updates, possibly the system 256 update, communication between machines on the LAN using ipv6 such as ping and ssh commands no longer work.

I have a ULA ipv6 address set in the .network file in the [ADDRESS] stanza on each machine, and run systemd-networkd with iwd for wireless. Using ping to the name or ULA address of another machine in the LAN fails, but ping -4 and ssh -4 work fine.

I have been battling this and trying to find a solution for some time, and yesterday came across these two system issue reports that suggest ipv6 forwarding is broken in systemd 256: https://github.com/systemd/systemd/issues/33414 and https://github.com/systemd/systemd/pull/33457 and although I am not running my machines as routers, it seems possible that the handling of ipv6 in systemd has bugs that are yet to be fixed.

If I use systemctl restart iwd, with IPv6Forwarding=yes in networkd.conf then once only the ping command works to another machine on my LAN, and repeating the command fails consistently unless I restart iwd again, which leads to the ping command to the second machine working once, and once only, again.

Does anyone else have an issue with ipv6 handling within the LAN for ULA addresses?  If so is there  any workaround for the current ipv6 problems in systemd-networkd?

Last edited by mcloaked (2024-06-29 13:37:39)

---

Mike C

mcloaked

Member

From: Yorkshire, UK

Registered: 2012-02-02

Posts: 1,360

Re: [SOLVED]ip6 ping/ssh between two machines with ULA fails after updates

I appear to have solved this by a change that I did not think was important - all I did was to change the ULA addresses in all the machines from fd00:xxxx:xxxx:xxxx::y/64 to  fd00:xxxx:xxxx:xxxx::y/48 in the address stanza of the asscoiated .network files, and restart systemd-networkd.  That change alone seems to have got it working consistently again, so perhaps it was just my misunderstanding of how ipv6 works!

---

Mike C