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Linux flushes an interface's IPv6 addresses when the link goes down, so `Iface::link_up` failed with EHOSTUNREACH when re-adding the v6 default route on any dual-stack device: the gateway was no longer on-link. We now set `keep_addr_on_down=1` in every namespace so global addresses survive the transition. The kernel drops link-local addresses regardless of that sysctl, so `link_up` re-adds the seeded link-local as well. Closes #46
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Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
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Iface::link_upfailed with EHOSTUNREACH on any dual-stack device afterlink_down, because Linux flushes IPv6 addresses when a link goes down and the v6 default route then has no on-link gateway. Every namespace now setskeep_addr_on_down=1so global addresses survive the transition. The kernel drops link-local addresses regardless of that sysctl, solink_upalso re-adds the seeded link-local. Addresses and the default routes come back; routes added outside patchbay do not.We keep addresses with the sysctl instead of re-adding the ones patchbay tracks. The sysctl also preserves addresses patchbay does not know about, and it makes an admin down issued from user code recoverable. Re-adding tracked addresses covers neither case and would still need the link-local special case.
The sysctl changes kernel behavior in every namespace, routers included. Nothing in patchbay takes router interfaces down, so in practice this only affects device
link_down, which did not work on dual-stack before.With
Ipv6Profile::Realistic, the kept addresses rerun duplicate address detection afterlink_up, so v6 is usable about two seconds later. That matches initial setup in that profile, and thelink_updocs now say so.The new
link_down_up_dual_stacktest reproduces the failure from the issue and checks that both v6 addresses and v6 connectivity are back after the flap. TheRouterPreset::Homescenario from the issue and the realistic profile were also checked by hand.Closes #46
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