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labsim: hard failover and reboot safety hold; runbook for the production apply Hard failover proven by destroying the master outright (virsh destroy -- no PADT, the case a graceful stop cannot cover): the survivor took the VIPs, dialled, and the access concentrator showed exactly ONE simdsl session from its MAC for the whole seven minutes. When the destroyed router came back it did NOT dial -- ConditionResult=no, ActiveState=inactive, NRestarts=0, pppoe0 absent, may_dial=no -- and the AC session count stayed at 1. That is the gate doing the one job it exists for, on the path that previously had no protection at all. Two more harness bugs of the same family as the last three, both of which reported a working system as broken: - ppp_on() returned an EMPTY string for an unreachable router, and `[ "" = 0 ]` is false, so the hard-failover wait sat for its full timeout waiting for a DESTROYED box to report zero -- long after the survivor had taken over correctly. Absent now means 0. - a VM restart recreates its taps under new names and the OVS bond keeps the old ones: lacp dies, VLAN 1 goes with it, and the box returns reachable on some VLANs and not others. That looked exactly like a failed failover. It is the same stale-membership fault ovs_bond_router already detects, but nothing ran it after a restart; the harness now does. migration/PPPOE-HA.md is the runbook: what the design is, why `disable` cannot work, the measured numbers, the deploy order (vyos002 first, on its own commit, verified on the wire with tcpdump rather than from state), and the one-line rollback. It also records a model hazard found while writing it. The imported baseline captures the RUNNING state, not the safe one -- vyos001 has no `vif 53 disable` because it happens to be master, vyos002 does. An apply performed while vyos002 held the VIP would therefore enable vyos001's WAN too, putting the cloned MAC on both boxes. An override must assert `vif 53 disable` on BOTH, accepting that an apply then briefly disables the current master's 10 gig until the reconciler restores it. Still not applied to production. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01DMVzWZgiKW2wquf5z8S1yH
2026-09-05 19:21:13 +01:00
# PPPoE high availability
Proven in labsim. **Not applied to production.**
## What it does
One consumer ISP account, two routers. The 10 gig lease is bound to a cloned MAC
(`f0:9f:c2:12:9b:4f`, the retired USG's) and the Vodafone line to a single
credential, so neither may be live on both boxes. The WAN follows VRRP
mastership — but the two halves use different control planes, and that is the
whole design:
| | plane | why |
|---|---|---|
| `bond0.53` (10 gig) | VyOS **config** (`disable`) | only config can move a MAC |
| `pppoe0` (Vodafone) | **systemd** unit gate | see below |
## Why PPPoE cannot live on the config plane
`interfaces_pppoe.py` treats `disable` and `delete` identically: both **unlink
`/etc/ppp/peers/pppoe0`**, call `PPPoEIf.remove()` (withdrawing the FRR default
route) and stop the unit. That path is pppd's own options file
(`ExecStart=/usr/sbin/pppd call %I`), so the resting state destroyed exactly what
the promotion path needed. `ppp@pppoe0` then restart-looped against the missing
file — 47 restarts observed, zero sessions at the access concentrator — and
never tripped systemd's limiter, because `RestartSec=5s` against the default
10s/5-burst window is only two restarts per interval.
It also made op-mode `connect interface pppoe0` unusable (it refuses without the
peers file), and put every failover behind a priority-322 commit where one
unrelated invalid node fails the whole thing.
## The gate
`pppoe0` is configured identically and **enabled on both** routers, so the peers
file always exists. Dialling is gated by
`/etc/systemd/system/ppp@pppoe0.service.d/10-vrrp-wan-gate.conf`:
```ini
ConditionPathExists=/run/vrrp-wan/may-dial
ConditionPathExists=/etc/ppp/peers/pppoe0
StartLimitIntervalSec=600
StartLimitBurst=6
```
`/run` is tmpfs, so the gate is shut at boot and neither box can dial before VRRP
has decided. **This is load-bearing, not a nicety:** with the node enabled,
`interfaces_pppoe.py` restarts ppp on *every* commit touching the pppoe subtree
when the daemon is not running — so the backup actively tries to dial whenever
anything commits (`pulumi up`, a hand commit, the boot-time config load). The
gate is the only thing making that a no-op, which is why `vrrp-wan-reconcile`
**refuses to bless a box whose drop-in is missing**: `/etc` is per-image, so a
VyOS upgrade silently removes the protection, and failing closed turns that into
"PPPoE never dials" rather than "both routers dial".
`may-dial` is a **lease, not a flag**. `ConditionPathExists` is evaluated at
start only — it can prevent a dial, never revoke one. `vrrp-wan-reconcile`
renews it every 30s; `vrrp-wan-guard` runs every 5s and only ever revokes, on
either "I do not hold the VIP" or "the lease is stale".
## Measured in labsim
| | |
|---|---|
PPPOE-HA: record the two failure modes found by running the thing Both were invisible to inspection and only appeared under the hard matrix: the flap damper tearing down an established session via the lease it stopped renewing, and a missing peers file being completely silent. The second has a production edge worth spelling out -- an unsaved commit reverts on reboot and takes pppoe0 with it, leaving a standby that can never take over while looking perfectly healthy.
2026-09-06 00:11:32 +01:00
| Clean failover (`force-fault`) | `pppoe0` moves in **20-26s**, reproducible |
labsim: hard failover and reboot safety hold; runbook for the production apply Hard failover proven by destroying the master outright (virsh destroy -- no PADT, the case a graceful stop cannot cover): the survivor took the VIPs, dialled, and the access concentrator showed exactly ONE simdsl session from its MAC for the whole seven minutes. When the destroyed router came back it did NOT dial -- ConditionResult=no, ActiveState=inactive, NRestarts=0, pppoe0 absent, may_dial=no -- and the AC session count stayed at 1. That is the gate doing the one job it exists for, on the path that previously had no protection at all. Two more harness bugs of the same family as the last three, both of which reported a working system as broken: - ppp_on() returned an EMPTY string for an unreachable router, and `[ "" = 0 ]` is false, so the hard-failover wait sat for its full timeout waiting for a DESTROYED box to report zero -- long after the survivor had taken over correctly. Absent now means 0. - a VM restart recreates its taps under new names and the OVS bond keeps the old ones: lacp dies, VLAN 1 goes with it, and the box returns reachable on some VLANs and not others. That looked exactly like a failed failover. It is the same stale-membership fault ovs_bond_router already detects, but nothing ran it after a restart; the harness now does. migration/PPPOE-HA.md is the runbook: what the design is, why `disable` cannot work, the measured numbers, the deploy order (vyos002 first, on its own commit, verified on the wire with tcpdump rather than from state), and the one-line rollback. It also records a model hazard found while writing it. The imported baseline captures the RUNNING state, not the safe one -- vyos001 has no `vif 53 disable` because it happens to be master, vyos002 does. An apply performed while vyos002 held the VIP would therefore enable vyos001's WAN too, putting the cloned MAC on both boxes. An override must assert `vif 53 disable` on BOTH, accepting that an apply then briefly disables the current master's 10 gig until the reconciler restores it. Still not applied to production. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01DMVzWZgiKW2wquf5z8S1yH
2026-09-05 19:21:13 +01:00
| 10 gig down → PPPoE | route falls to `pppoe0`; LAN back online in **5s** |
| Stale lease | guard hangs up within ~5s |
| Missing peers file | `NRestarts=0` — no loop |
PPPOE-HA: record the two failure modes found by running the thing Both were invisible to inspection and only appeared under the hard matrix: the flap damper tearing down an established session via the lease it stopped renewing, and a missing peers file being completely silent. The second has a production edge worth spelling out -- an unsaved commit reverts on reboot and takes pppoe0 with it, leaving a standby that can never take over while looking perfectly healthy.
2026-09-06 00:11:32 +01:00
| Flap holdoff vs live session | session survives a forged 900s holdoff |
labsim: hard failover and reboot safety hold; runbook for the production apply Hard failover proven by destroying the master outright (virsh destroy -- no PADT, the case a graceful stop cannot cover): the survivor took the VIPs, dialled, and the access concentrator showed exactly ONE simdsl session from its MAC for the whole seven minutes. When the destroyed router came back it did NOT dial -- ConditionResult=no, ActiveState=inactive, NRestarts=0, pppoe0 absent, may_dial=no -- and the AC session count stayed at 1. That is the gate doing the one job it exists for, on the path that previously had no protection at all. Two more harness bugs of the same family as the last three, both of which reported a working system as broken: - ppp_on() returned an EMPTY string for an unreachable router, and `[ "" = 0 ]` is false, so the hard-failover wait sat for its full timeout waiting for a DESTROYED box to report zero -- long after the survivor had taken over correctly. Absent now means 0. - a VM restart recreates its taps under new names and the OVS bond keeps the old ones: lacp dies, VLAN 1 goes with it, and the box returns reachable on some VLANs and not others. That looked exactly like a failed failover. It is the same stale-membership fault ovs_bond_router already detects, but nothing ran it after a restart; the harness now does. migration/PPPOE-HA.md is the runbook: what the design is, why `disable` cannot work, the measured numbers, the deploy order (vyos002 first, on its own commit, verified on the wire with tcpdump rather than from state), and the one-line rollback. It also records a model hazard found while writing it. The imported baseline captures the RUNNING state, not the safe one -- vyos001 has no `vif 53 disable` because it happens to be master, vyos002 does. An apply performed while vyos002 held the VIP would therefore enable vyos001's WAN too, putting the cloned MAC on both boxes. An override must assert `vif 53 disable` on BOTH, accepting that an apply then briefly disables the current master's 10 gig until the reconciler restores it. Still not applied to production. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01DMVzWZgiKW2wquf5z8S1yH
2026-09-05 19:21:13 +01:00
| Invariant | AC never showed two `simdsl` sessions |
PPPOE-HA: record the two failure modes found by running the thing Both were invisible to inspection and only appeared under the hard matrix: the flap damper tearing down an established session via the lease it stopped renewing, and a missing peers file being completely silent. The second has a production edge worth spelling out -- an unsaved commit reverts on reboot and takes pppoe0 with it, leaving a standby that can never take over while looking perfectly healthy.
2026-09-06 00:11:32 +01:00
## Two failure modes found by running it, not by reading it
**The flap damper tore down a healthy WAN.** `ppp_dial()` checked the hold-off
and returned *before* renewing `may-dial`. That file is a lease the guard
expires after `LEASE_TTL`, so tripping the damper stopped the renewal and the
guard hung up `pppoe0` **on the master** ~80s later:
```
DIAL FLAP: >=6 attempts in 600s -- holding off 900s
GUARD: lease stale (81s > 75s) -- hanging up pppoe0
```
A damper meant to suppress repeated *dials* was destroying an established
session instead. An active session now renews the lease and returns before
every other check; everything below only decides whether to start a **new**
session. T12 is the regression test.
**A missing peers file is silent.** `/etc/ppp/peers/pppoe0` is both pppd's
options file and the gate's second condition, and it is only written by a commit
that touches the pppoe subtree. Without it systemd logs
`skipped because of an unmet condition check` exactly once and then nothing —
a router that cannot dial at all looks identical to a healthy backup.
`ppp_dial()` now says so on every tick, and distinguishes the two causes:
configured-but-not-rendered (re-commit the subtree) versus no `pppoe0` in the
config at all.
The second cause is the one to watch in production: **a commit that was never
`save`d reverts on reboot and takes `pppoe0` with it.** That is exactly how the
sim secondary lost its WAN and spent hours looking like an ISP problem. After
any hand commit to the pppoe subtree, `save` — or the next reboot produces a
standby that can never take over.
labsim: hard failover and reboot safety hold; runbook for the production apply Hard failover proven by destroying the master outright (virsh destroy -- no PADT, the case a graceful stop cannot cover): the survivor took the VIPs, dialled, and the access concentrator showed exactly ONE simdsl session from its MAC for the whole seven minutes. When the destroyed router came back it did NOT dial -- ConditionResult=no, ActiveState=inactive, NRestarts=0, pppoe0 absent, may_dial=no -- and the AC session count stayed at 1. That is the gate doing the one job it exists for, on the path that previously had no protection at all. Two more harness bugs of the same family as the last three, both of which reported a working system as broken: - ppp_on() returned an EMPTY string for an unreachable router, and `[ "" = 0 ]` is false, so the hard-failover wait sat for its full timeout waiting for a DESTROYED box to report zero -- long after the survivor had taken over correctly. Absent now means 0. - a VM restart recreates its taps under new names and the OVS bond keeps the old ones: lacp dies, VLAN 1 goes with it, and the box returns reachable on some VLANs and not others. That looked exactly like a failed failover. It is the same stale-membership fault ovs_bond_router already detects, but nothing ran it after a restart; the harness now does. migration/PPPOE-HA.md is the runbook: what the design is, why `disable` cannot work, the measured numbers, the deploy order (vyos002 first, on its own commit, verified on the wire with tcpdump rather than from state), and the one-line rollback. It also records a model hazard found while writing it. The imported baseline captures the RUNNING state, not the safe one -- vyos001 has no `vif 53 disable` because it happens to be master, vyos002 does. An apply performed while vyos002 held the VIP would therefore enable vyos001's WAN too, putting the cloned MAC on both boxes. An override must assert `vif 53 disable` on BOTH, accepting that an apply then briefly disables the current master's 10 gig until the reconciler restores it. Still not applied to production. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01DMVzWZgiKW2wquf5z8S1yH
2026-09-05 19:21:13 +01:00
## Deploying (not yet done)
1. `sudo /config/vyos-known-good save` on both.
2. `migration/vrrp-wan-install --vip 192.168.1.1 --host vyos@10.0.1.253` then the
same for `.252`. Then `--check` on both. **No config change yet** — verify
nothing dials.
3. Confirm `/config/wan-secrets` is present and identical on both.
4. **vyos002 first** (the non-master), on its own commit — `interfaces pppoe` is
priority 322 and one bad node fails everything:
`delete interfaces pppoe pppoe0 disable`, `commit-confirm 10`.
5. Verify vyos002 did **not** dial — check on the wire, not from state:
`sudo tcpdump -i bond0.51 -nn pppoed` should show no PADI. Then `confirm`; `save`.
6. vyos001: nothing to change; it already has `pppoe0` enabled.
7. Confirm `vif 53 disable` is in **both** `config.boot`s.
vrrp-wan: size GRACE from the measured hostile failover, not the theory With the matrix actually setting session-control, T4 timed a destroyed master's takeover at: replace 26s deny 148s <-- sizing case disable 21s `deny` is the case GRACE exists for: the AC refuses the survivor until its own dead-peer timer frees the dead session. The session poller caught it happening -- the destroyed router's session stayed in the table while the survivor's dials appeared and were rejected, twice, before one took at 148s. 148s is well past the lcp-echo-interval(30) x failure(3) = 90s budget that 180 was sized against, leaving 32s of margin. GRACE=300 is ~2x the worst observed. Treat 148s as a floor, not a worst case: these are idle 2-vCPU VMs, and the AC shares an OVS bridge with the routers, so `virsh destroy` removes the port and accel-ppp sees the peer vanish. A real BRAS over DSL never learns our router died and waits out longer timers of its own. The cost is stated in the conf: GRACE is also how long an alive-but-unroutable master holds every VIP before yielding. bond0.53 covers most of that -- a DHCP lease satisfies the check in seconds -- so GRACE only dominates when PPPoE is the last path. Kept the health check's fallback in step, since keepalived runs it with no environment and that number decides mastership if the conf is ever missing. check_invariant no longer fails blind on the AC's session count. That count is only a proxy for "two of our routers dialled", and only while the AC enforces single-session; under `disable` it does not, so a destroyed router's session lingers and the count reads 2 with exactly one live router dialled. The real invariant -- at most one router holds pppoe0 -- is now the failing one, and the stale session is reported as a WARN rather than silenced, because it still occupies the slot at a real ISP and is precisely what made `deny` take 148s.
2026-09-06 00:25:00 +01:00
8. **Only now** merge `migration/pulumi-override-pppoe-gated.json` into
`kubernetes-deployment` `infra/vyos/subtrees/overrides.json`. It is staged
here, unapplied, on purpose: another agent runs `pulumi up` on that repo, so
merging it *is* a production change made by someone else at a time you do not
choose. Removing `pppoe0 disable` from vyos002 before the gate exists there
lets it dial on the next commit and take the single Vodafone session off
vyos001. Run `npm run vyos:export && npm run vyos:render` first so the model
follows whichever router actually holds the WAN.
9. Add the drop-in re-install to the VyOS image-upgrade runbook.
Step 4 is the one that matters most and is worth stopping on. vyos002 has been
in **FAULT on all six groups for over three days** — verified again while
writing this, alongside vyos001 holding `192.168.1.1` on `bond0.1` and
`pppoe0` up on `83.106.5.72`. Until vyos002 reaches BACKUP there is no standby
at all: if vyos001 died today nothing would pick up the gateway VIPs. The
existing `vrrp-health-check-wan-present` override predicted exactly this in its
own reason text — *"with the primary genuinely dead the secondary stays FAULT
and nothing holds the gateway. The fix for that is WAN-follows-master, which is
a separate change."* This is that change.
labsim: hard failover and reboot safety hold; runbook for the production apply Hard failover proven by destroying the master outright (virsh destroy -- no PADT, the case a graceful stop cannot cover): the survivor took the VIPs, dialled, and the access concentrator showed exactly ONE simdsl session from its MAC for the whole seven minutes. When the destroyed router came back it did NOT dial -- ConditionResult=no, ActiveState=inactive, NRestarts=0, pppoe0 absent, may_dial=no -- and the AC session count stayed at 1. That is the gate doing the one job it exists for, on the path that previously had no protection at all. Two more harness bugs of the same family as the last three, both of which reported a working system as broken: - ppp_on() returned an EMPTY string for an unreachable router, and `[ "" = 0 ]` is false, so the hard-failover wait sat for its full timeout waiting for a DESTROYED box to report zero -- long after the survivor had taken over correctly. Absent now means 0. - a VM restart recreates its taps under new names and the OVS bond keeps the old ones: lacp dies, VLAN 1 goes with it, and the box returns reachable on some VLANs and not others. That looked exactly like a failed failover. It is the same stale-membership fault ovs_bond_router already detects, but nothing ran it after a restart; the harness now does. migration/PPPOE-HA.md is the runbook: what the design is, why `disable` cannot work, the measured numbers, the deploy order (vyos002 first, on its own commit, verified on the wire with tcpdump rather than from state), and the one-line rollback. It also records a model hazard found while writing it. The imported baseline captures the RUNNING state, not the safe one -- vyos001 has no `vif 53 disable` because it happens to be master, vyos002 does. An apply performed while vyos002 held the VIP would therefore enable vyos001's WAN too, putting the cloned MAC on both boxes. An override must assert `vif 53 disable` on BOTH, accepting that an apply then briefly disables the current master's 10 gig until the reconciler restores it. Still not applied to production. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01DMVzWZgiKW2wquf5z8S1yH
2026-09-05 19:21:13 +01:00
**Rollback**, from either box: `set interfaces pppoe pppoe0 disable` on both and
`rm /run/vrrp-wan/may-dial`. That restores today's behaviour exactly.
## What the sim cannot prove
vrrp-wan: size GRACE from the measured hostile failover, not the theory With the matrix actually setting session-control, T4 timed a destroyed master's takeover at: replace 26s deny 148s <-- sizing case disable 21s `deny` is the case GRACE exists for: the AC refuses the survivor until its own dead-peer timer frees the dead session. The session poller caught it happening -- the destroyed router's session stayed in the table while the survivor's dials appeared and were rejected, twice, before one took at 148s. 148s is well past the lcp-echo-interval(30) x failure(3) = 90s budget that 180 was sized against, leaving 32s of margin. GRACE=300 is ~2x the worst observed. Treat 148s as a floor, not a worst case: these are idle 2-vCPU VMs, and the AC shares an OVS bridge with the routers, so `virsh destroy` removes the port and accel-ppp sees the peer vanish. A real BRAS over DSL never learns our router died and waits out longer timers of its own. The cost is stated in the conf: GRACE is also how long an alive-but-unroutable master holds every VIP before yielding. bond0.53 covers most of that -- a DHCP lease satisfies the check in seconds -- so GRACE only dominates when PPPoE is the last path. Kept the health check's fallback in step, since keepalived runs it with no environment and that number decides mastership if the conf is ever missing. check_invariant no longer fails blind on the AC's session count. That count is only a proxy for "two of our routers dialled", and only while the AC enforces single-session; under `disable` it does not, so a destroyed router's session lingers and the count reads 2 with exactly one live router dialled. The real invariant -- at most one router holds pppoe0 -- is now the failing one, and the stale session is reported as a WARN rather than silenced, because it still occupies the slot at a real ISP and is precisely what made `deny` take 148s.
2026-09-06 00:25:00 +01:00
- **Vodafone's `session-control`.** The matrix now brackets it properly.
Destroying the master and timing the survivor's session:
| policy | takeover |
|---|---|
| `replace` (accel-ppp default) | 26s |
| **`deny`** (hostile) | **148s** |
| `disable` | 21s |
`deny` is the sizing case: the AC refuses the survivor until its own
dead-peer timer frees the dead session, and the poller caught two dial
attempts being rejected before one succeeded. `GRACE` is set from that — see
`migration/vrrp-wan.conf`. This still cannot tell you which policy Vodafone
runs, and account rate-limiting or lockout on repeated dials has no sim
analogue at all; the flap damper (6 dials / 600s → 15 min hold-off) exists
for that.
Treat the 148s as a floor rather than a worst case. These are idle 2-vCPU
VMs, and the AC shares an OVS bridge with the routers, so `virsh destroy`
removes the port and accel-ppp sees the peer physically vanish. A real BRAS
reached over DSL does not learn that our router died — it waits out its own
timers, which are longer and not ours to know.
Worth knowing how close this came to being missed: until 2026-09-06 the
matrix set the policy with `vbash -c 'source script-template; configure;
...; commit'`, which never starts a config session. `commit` failed to
stderr, the helper discarded it, and all three iterations ran against the
default while printing the mode they were supposedly testing. It reported
`deny` at 25s. The real figure is 148s.
labsim: hard failover and reboot safety hold; runbook for the production apply Hard failover proven by destroying the master outright (virsh destroy -- no PADT, the case a graceful stop cannot cover): the survivor took the VIPs, dialled, and the access concentrator showed exactly ONE simdsl session from its MAC for the whole seven minutes. When the destroyed router came back it did NOT dial -- ConditionResult=no, ActiveState=inactive, NRestarts=0, pppoe0 absent, may_dial=no -- and the AC session count stayed at 1. That is the gate doing the one job it exists for, on the path that previously had no protection at all. Two more harness bugs of the same family as the last three, both of which reported a working system as broken: - ppp_on() returned an EMPTY string for an unreachable router, and `[ "" = 0 ]` is false, so the hard-failover wait sat for its full timeout waiting for a DESTROYED box to report zero -- long after the survivor had taken over correctly. Absent now means 0. - a VM restart recreates its taps under new names and the OVS bond keeps the old ones: lacp dies, VLAN 1 goes with it, and the box returns reachable on some VLANs and not others. That looked exactly like a failed failover. It is the same stale-membership fault ovs_bond_router already detects, but nothing ran it after a restart; the harness now does. migration/PPPOE-HA.md is the runbook: what the design is, why `disable` cannot work, the measured numbers, the deploy order (vyos002 first, on its own commit, verified on the wire with tcpdump rather than from state), and the one-line rollback. It also records a model hazard found while writing it. The imported baseline captures the RUNNING state, not the safe one -- vyos001 has no `vif 53 disable` because it happens to be master, vyos002 does. An apply performed while vyos002 held the VIP would therefore enable vyos001's WAN too, putting the cloned MAC on both boxes. An override must assert `vif 53 disable` on BOTH, accepting that an apply then briefly disables the current master's 10 gig until the reconciler restores it. Still not applied to production. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01DMVzWZgiKW2wquf5z8S1yH
2026-09-05 19:21:13 +01:00
- **Whether Vodafone honours our LCP Terminate / PADT** on a graceful stop.
- **The cloned-MAC lease** — whether the 10 gig ISP re-issues `87.192.101.48` to
`f0:9f:c2:12:9b:4f` arriving on a different switch port. That risk belongs to
`bond0.53`, not PPPoE, and is the largest untested item in the failover.
- **Real dial time and MTU/MSS under load.** PPPoE was proven on the *USG*;
VyOS dialling Vodafone has never been done.
- **Timing under load.** The sim routers are idle 2-vCPU VMs; commit latency on
the VP2440s under kea + BGP + conntrack will be worse, and commit latency is
the dominant term in the `bond0.53` half of a failover.
## A model hazard to fix before applying
The imported baseline records the **running** state, not the safe one: vyos001
has no `vif 53 disable` (it is master), vyos002 does. So an apply performed while
vyos002 held the VIP would enable vyos001's WAN as well, putting the cloned MAC
on both boxes. An override must assert `vif 53 disable` on **both** routers, with
the reconciler re-enabling whichever holds the VIP. Note the consequence: an
apply then briefly disables the current master's 10 gig until the reconciler
restores it (≤30s).
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