Mat Kowalski 15a8ca3881 optional DAD skip for managed VIP addresses ...

This PR adds an explicit configuration option `vip_skipdad`. This allows
for a proper behaviour in IPv6 networks with RT mode and ECMP. Without
this option only one node can ever hold the same IPv6 VIP what defeats
the purpose of ECMP.

While the ARP mode currently has a recovery mode for failed DAD, RT mode
misses it. It is also more feasible to use config option, as recovery
mode in RT mode would always introduce a ~5s blackholing (we know there
will be a conflict, so first attempt to add a VIP will fail and only the
next one will force IFA_F_NODAD).

For simplicitly we ignore IPv4/IPv6 checks, as kernel transparently
strips IFA_F_NODAD from v4 addresses without throwing errors.

For systems with IPv4 duplicate detection (called ACD and used e.g. in
RHEL10's NetworkManager) this code has no effect as it's only userspace
action and addresses we add via netlink bypass any check.

First discovered on a dual-stack cluster with two routing-table-mode
advertisers: the ingress VIP answered or timed out depending on which
ECMP path the flow hashed to; with NODAD both advertisers accept
traffic.

Signed-off-by: Mat Kowalski <mko@redhat.com>

2026-08-07 13:40:23 +02:00

..

instance.go

optional DAD skip for managed VIP addresses

2026-08-07 13:40:23 +02:00