DHCP troubleshooting: scopes, leases and relay
For network and systems administrators and MSP technicians who look after DHCP servers and the routers or layer 3 switches that relay DHCP between subnets. You should already know the discover, offer, request and acknowledge exchange and how a scope is built (see DHCP server design and DHCP from the client side); for reading packet captures in depth, see the Wireshark course. This course works from the server side: placing a fault on the client, relay path or server, checking a server's service, authorization, bindings and scope statistics, reading the Windows DHCP audit log, verifying relays through giaddr and scope selection, and calculating lease timers so you can predict who an outage will affect. Grounded in RFC 2131, 2132, 1542 and 3046 and Microsoft's DHCP troubleshooting guidance; your change process decides who may change scopes and relays. Ends with a supervisor-graded troubleshooting case.
- Level
- Intermediate
- Length
- About 95 minutes
- Contents
- 5 lessons · final exam
- Status
- Published · updated 10 Oct 2026
Skills you'll practise
- Narrow a DHCP fault to the client, the relay path or the server by asking who is affected, since when and what changed
- Check a DHCP server's service, authorization, bindings and scope statistics, and identify an exhausted or conflicting scope
- Interpret DHCP audit log events and lease messages such as address-in-use, pool exhausted, DECLINE and NAK
- Verify a DHCP relay (IP helper) using giaddr, and explain how the server chooses the scope for a relayed client
- Calculate renewal (T1), rebinding (T2) and expiry times and predict which clients a DHCP server outage will affect
Course outline
- 1.Narrow a DHCP fault: client, relay path or serverLesson · 16 min
- 2.Check the DHCP server: service, authorization, bindings and scope statisticsLesson · 16 min
- 3.Interpret DHCP audit log events and lease messagesLesson · 15 min
- 4.Verify a DHCP relay using giaddr and scope selectionLesson · 16 min
- 5.Calculate lease timers and predict the impact of a server outageLesson · 14 min
- 6.DHCP troubleshooting: scopes, leases and relay: knowledge checkKnowledge check · 15 questions
- 7.DHCP troubleshooting: scopes, leases and relay: practical exerciseKnowledge check · 1 question
- 8.Final exam10 questions · passing it completes the course, so people who already know the material can test out
Sources it draws on
The lessons and questions are written from these references, so learners can go back to the original.
- RFC 2131: Dynamic Host Configuration Protocol (giaddr, scope selection, NAK and DECLINE handling, T1/T2 timers, lease expiry)
- RFC 2132: DHCP Options and BOOTP Vendor Extensions (router, DNS server, lease time, message type, server identifier, T1/T2 options)
- RFC 1542: Clarifications and Extensions for the Bootstrap Protocol (relay agent behaviour: giaddr, hops, destinations)
- RFC 3046: DHCP Relay Agent Information Option (option 82, circuit ID and remote ID)
- Microsoft Learn: DHCP troubleshooting guidance (checklist, server and client checks, two-sided network trace)
- Microsoft Learn: Troubleshooting guide for DHCP (components, renew at 50% and rebind at 87.5% of the lease, UDP 67 and 68)
- Microsoft Learn (previous versions, Windows Server 2008 R2): More About DHCP Audit and Event Logging (log format and event IDs)
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