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Troubleshoot — a DHCP server that has no pool for this LAN
Enterprise Beginner 4 devices 3 checked tasks 100 points Free lab
New PCs on the branch LAN get no address — or one with an address like 169.254. The DHCP server is a router in the next room and it is answering. Check what the router thinks the LAN is: a pool is only used for requests that arrive from a network it covers. You build it in a browser, type real commands at each device, and every task below is
checked against the running configuration — so you find out it is wrong before anybody else does.
Open this lab in the simulator
The simulator runs in your browser with nothing to install. This is a free lab: it stays open on the free plan. It needs an account, which keeps your progress.
The scenario
New PCs on the branch LAN get no address — or one with an address like 169.254. The DHCP server is a router in the next room and it is answering. Check what the router thinks the LAN is: a pool is only used for requests that arrive from a network it covers.
Your role: a network engineer on the enterprise team. Level: Beginner Done when: all 3 goals show as passed (100 points).
Network status
Devices: 1 router, 1 switch, 2 PCs, cabled as drawn. No Layer 1 or Layer 2 faults: every link is connected and up. R1-DHCP starts with addresses (G0/0 10.20.0.1/24) and a DHCP pool already configured. SW1 starts with an empty configuration. Known problems
The network worked and now does not: the scenario above says what users report. The cause is a configuration fault, not a cable. Find it with show commands (interfaces, routes, neighbours, running-config) before you change anything; fix only what is wrong. Goals
The pool covers the LAN the router is attached to (10.20.0.0/24) (40 pts) PC1 leases an address (30 pts) PC2 leases one and reaches the gateway (30 pts) The activity, in order
The pool covers the LAN the router is attached to (10.20.0.0/24) Why: This is the task that checks your configuration directly: the line must really be there, not just look right. Verify with: show running-config PC1 leases an address Why: If the host has no address, look at the pool, the exclusions and, across a router, the ip helper-address. Verify with: ipconfig PC2 leases one and reaches the gateway Why: If the host has no address, look at the pool, the exclusions and, across a router, the ip helper-address. Verify with: ipconfig Tips
Work in the order given: later goals depend on the earlier ones. After every change, run the verify command before moving on; do not guess. Stuck? Read the verify output first. It names the interface, neighbour or route that is wrong. Common mistake: Typing the right network on the wrong pool name Common mistake: Excluded addresses that cover the whole range Common mistake: A relay that points at the wrong server Why this matters
A DHCP pool is chosen by the subnet the request arrives from. A pool for the wrong network never matches, so clients get nothing or a 169.254 address.
What you will be able to do
Match a pool’s network to the interface it serves
Read show ip dhcp pool and binding
Renew a lease and verify address, mask, gateway and DNS
The network
ISR 2911, Catalyst 2960-24TT, PC — 4 devices in all, already cabled.
Fa0/1 Fa0 Fa0/2 Fa0 Gi0/1 Gi0/0 10.20.0.1/24 R1-DHCP SW1 PC1 PC2 Drawn from this lab: devices, cables, ports and the addresses already set. Device Model Address already set
R1-DHCP ISR 2911 configure it SW1 Catalyst 2960-24TT configure it PC1 PC configure it PC2 PC configure it
Cabling
SW1 Fa0/1 ↔ PC1 Fa0 SW1 Fa0/2 ↔ PC2 Fa0 SW1 Gi0/1 ↔ R1-DHCP Gi0/0
What is configured at the start
These are already configured when the lab opens — including, where this is a troubleshooting lab, the fault itself:
R1-DHCP interface g0/0
ip address 10.20.0.1 255.255.255.0
no shutdown
exit
ip dhcp excluded-address 10.20.0.1 10.20.0.9
ip dhcp pool BRANCH
network 10.21.0.0 255.255.255.0
default-router 10.21.0.1
dns-server 10.21.0.1
exit Tasks, and how each one is checked
Every task is decided by reading the live network — a neighbour in FULL, a ping that succeeds, a line in the running configuration — not by looking for a keyword you typed. The same command shows you what the lab sees.
# Task Pts How to verify it yourself
1 The pool covers the LAN the router is attached to (10.20.0.0/24) 40 On R1-DHCP: show running-config contains the line(s) matching ip dhcp pool BRANCH … network 10\.20\.0\.0 255\.255\.255\.0. 2 PC1 leases an address 30 On PC1: ipconfig shows an address. 3 PC2 leases one and reaches the gateway 30 On PC2: ipconfig shows an address. and On PC2: ping 10.20.0.1 must succeed.
Stuck? Ask the coach
Tell the coach what you see or what you tried. It gives you a hint, not the answer, the way a senior engineer would. Included with a free trial or any plan.
Ask the coach
Common mistakes
Typing the right network on the wrong pool name
Excluded addresses that cover the whole range
A relay that points at the wrong server
Reference solution
Try it yourself first — the lab checks your work either way. This is one configuration that makes every task pass, device by device:
R1-DHCP no ip dhcp pool BRANCH
ip dhcp pool BRANCH
network 10.20.0.0 255.255.255.0
default-router 10.20.0.1
dns-server 10.20.0.1
exit PC1 ipconfig /renew PC2 ipconfig /renew Where this is examined
CCNA (DHCP), Network+ (DHCP troubleshooting).
This lab practises these topics in the zNetLaB certification courses:
DHCP, DNS, NTP, SNMP, Syslog — CCNA · IP Services Troubleshooting DHCP, NAT, SNMP, syslog, IP SLA, NetFlow — CCNP Enterprise · ENARSI · Infrastructure Services Service problems: DNS, DHCP, NAT, ACLs — CompTIA Network+ · Network Troubleshooting
Related labs
Where to start
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