TopicIT Networking →

⌚ About 3 min read

View my favorites

Real-world problem · V2

Quick troubleshooting view

What you are seeing

Customers no longer get lease after DHCP Snooping's DHCP.

Likely causes

infinite link non-RES.
STAT.
Option 82.

First checks

Limit the impact.
Collecting Evidence.
Test the the simplest hypothesis.

Recommended actions

Correct the confirmed cause rather than the symptom.
Document the change and result.
Establish supervision if the defect can recur.

Start Symptom → Cause →

BAOI

Contextual technician plan

Limit the impact.

Identify whether a position, service or entire site is affected.

Expected result

The client should receive a valid address, gateway and DNS from the intended scope/VLAN instead of APIPA or an unexpected network.

If OK

If the lease is correct, move to gateway/DNS/service reachability rather than changing DHCP.

If not OK

If the lease is missing or wrong, compare VLAN, relay, scope availability

RiskManual check

Collecting Evidence.

Keep the message accurate, time, and associated logs.

Expected result

The client should receive a valid address, gateway and DNS from the intended scope/VLAN instead of APIPA or an unexpected network.

If OK

If the lease is correct, move to gateway/DNS/service reachability rather than changing DHCP.

If not OK

If the lease is missing or wrong, compare VLAN, relay, scope availability and another client on the same access path.

RiskManual check

Test the the simplest hypothesis.

Compare with equipment or functional path.

Expected result

The client should receive a valid address, gateway and DNS from the intended scope/VLAN instead of APIPA or an unexpected network.

If OK

If the lease is correct, move to gateway/DNS/service reachability rather than changing DHCP.

If not OK

If the lease is missing or wrong, compare VLAN, relay, scope availability and another client on the same access path.

RiskManual check

Correct and validate.

Apply only one change at a time and retester.

Expected result

The client should receive a valid address, gateway and DNS from the intended scope/VLAN instead of APIPA or an unexpected network.

If OK

If the lease is correct, move to gateway/DNS/service reachability rather than changing DHCP.

If not OK

If the lease is missing or wrong, compare VLAN, relay, scope availability and another client on the same access path.

RiskManual check

✓

Validation after action

Repeat the same validation test after the correction and confirm the original symptom is gone. Validate stability before closing the incident.

↶

Change safety / rollback

Before changing configuration, record the current value and a way back.

When to escalate

Cadader if the impact extends, if the data are at risk or if the cause involves irreversible modification.

& Security NetworkIntermediate.

Customers no longer get lease after DHCP Snooping's DHCP.

Important: relevez toujours le message d’erreur exact et l’heure du problème avant de modifier la configuration. Les actions proposées doivent être adaptées à votre environnement.

Causes probables

infinite link non-RES.
STAT.
Option 82.

Diagnostic étape par étape

1
Limit the impact.
Identify whether a position, service or entire site is affected.
2
Collecting Evidence.
Keep the message accurate, time, and associated logs.
3
Test the the simplest hypothesis.
Compare with equipment or functional path.
4
Correct and validate.
Apply only one change at a time and retester.

Solutions possibles

Correct the confirmed cause rather than the symptom.
Document the change and result.
Establish supervision if the defect can recur.

Quand escalader ?

Cadader if the impact extends, if the data are at risk or if the cause involves irreversible modification.

← All les pannes Lancer un diagnostic guidé