Michal 395577850c IPv6 was never HA, and the WAN becoming HA is what exposed it ...

Reviewed the parked IPv6 task against the PPPoE-HA work of 2026-09-05/06. The
gate that parked it ("WI-8 before IPv6") is cleared, but the same work
invalidated the assumption the IPv6 design rested on.

Verified on the live routers: vyos002 has no tun0, no he-tunnel-follow, no
he-secrets, no VLAN 9 prefix and no route6 ::/0 -- only the pre-staged
default-deny v6 firewall, which is correctly on both. Failover is now automatic
and drill-proven, so every failover takes the whole v6 estate down for as long
as vyos002 holds the VIP.

Four things that came out of checking rather than reading:

- PPPOE-HA.md's "tun0 survived untouched and IPv6 stayed up at 15.5ms" does not
  follow from its own premise and is corrected in place. The endpoint address is
  stable, but it MOVES to vyos002, which has nothing to decapsulate protocol 41.
  wan-drill had no IPv6 check at all, which is why nobody caught it.
- A 22-second near-miss: vif53-pin-boot-disable bounced the 10 gig, he-tunnel-
  follow ticked once and saw the PPPoE address, and vyos-failover restored the
  route 22s before the second tick would have pointed HE at an address Vodafone
  reissues on every dial.
- VyOS does NOT leave a tunnel down when its source-address is absent (the
  override's stated reason for leaving IPv6 single-homed). Measured in labsim:
  it commits rc=0 and brings the link UP -- a blackhole that attracts the v6
  default route. The runtime gate is load-bearing, like the PPPoE gate.
- The RA link-mtu was pinned at 1480 while the tunnel correctly drops to 1472 on
  the PPPoE path.

Mechanism, mirroring PPPoE HA -- identical config on both, gated at runtime, no
commit in the failover path:

- vrrp-wan-reconcile: a v6 kernel plane. tun0 and radvd follow the VIP; radvd is
  stopped BEFORE the WAN goes so its farewell RA (router-lifetime 0) still has a
  path out. The WAN early-exits became if-blocks so the plane runs every tick.
  It deliberately does NOT call he-tunnel-follow: that would halve the
  hysteresis the near-miss above showed we depend on.
- he-tunnel-follow: a master guard reading the same vrrp-wan.conf VIP, so the
  backup copy cannot point HE at its own idle PPPoE line, plus a stubbable
  HE_UPDATE_URL.
- vrrp-wan-install carries both, so --check and the upgrade runbook cover IPv6.
- wan-drill measures IPv6 in both timing loops and asserts zero HE API calls
  across a router failover.

labsim finally has an HE endpoint, closing the gap the override itself cited as
why this was never rehearsed. Both ISP islands already share the libvirt network,
so that becomes the backbone and HE lives behind it on one address reachable over
either WAN. Proven in the sim: backup tun=DOWN radvd=inactive, master tun=UP
radvd=active, hysteresis then HE call then MTU 1480->1472, and VLAN 9 hosts
autoconfiguring from the RA. The end-to-end v6 datapath is NOT yet proven --
inter-island transit crosses libvirt NAT and the return path is lost. Recorded as
a KNOWN SIM GAP rather than papered over.

The model change is staged, not merged: another agent runs pulumi up on that
repo, and the gate must exist on vyos002 before the tunnel does.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DMVzWZgiKW2wquf5z8S1yH

2026-09-06 14:30:44 +01:00

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