ipconfig /all on an affected machine is the first evidence: address, lease times and the
"DHCP Server" field say whether this is no answer, the wrong answerer or the wrong answer.
Climb the Troubleshooting Ladder base skill first: past DHCP or "no network" tickets and
what changed (new AP or ISP router, VLAN work, a lease cleanup), then the documented design
— DHCP servers, scope ranges, failover, IP helper/relay location, reservation conventions.
Where Liongard covers it, use its inspector data and timeline (Inspector Read Discipline
base skill). Then release and renew and watch what answers; read scope stats, the event log
(1020, 1046, failover) and the lease list.
Branch:
1. APIPA or no answer at a site or VLAN — service down, scope deactivated, or a broken
relay. Broadcasts don't cross VLANs without an IP helper: if the server's own VLAN leases
fine and a remote one doesn't, it's the relay — the network owner's if they manage it.
2. Exhaustion (new devices fail, stats near 100%) — compare lease duration to churn; an
8-day default on a guest or BYOD VLAN exhausts fast, and outages leave stale leases. In
order: shorten the lease, widen the range, clear expired leases — never active ones,
which forces conflicts. Re-addressing escalates.
3. Wrong answer (unexpected range, wrong gateway/DNS) — read the "DHCP Server" field.
Unsanctioned means a rogue, usually a consumer router or an AP in router mode: trace its
MAC in the switch table, repatch it, recommend DHCP snooping. An untraceable rogue is the
network owner's, with the MAC evidence. If sanctioned, fix the scope options — wrong DNS
pairs with the internal DNS playbook.
4. Failover unhealthy — read both partners' state. Communication-interrupted with both up is
connectivity or time between them; partner-down means one is truly gone, and the survivor
takes full control only after the MCLT elapses or an operator confirms. Never rebuild or
deconfigure failover as a quick fix, and never add an overlapping scope — a
self-inflicted rogue.
5. Reservation vs exclusion — a reservation pins one IP to one MAC (device stays on DHCP);
an exclusion just stops the server handing that range out. Still leasing elsewhere after
a reservation: wrong MAC or another scope. Conflicts on "static" gear: the address sits
in the pool unexcluded. Fix per the documented convention.
Never restart the DHCP service or deactivate a scope to test a theory, and let the network
owner approve scope-option changes; a typo in gateway or DNS is a site outage. AD
authorization guards only against rogue Windows DHCP servers — consumer gear never asks AD.
Verify: the machine renews the right address and options from a sanctioned server, or scope
stats show headroom. Note it (PSA Note Discipline base skill): symptom, evidence, branch,
action or handoff, verification.
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