DHCP Clients Not Receiving IP Addresses

DHCP CLIENTS

I was setting up a small branch network and used the ISR router as the DHCP server. Everything looked fine—DHCP pool was there, interfaces were up, and the router was hooked to a switch with clients behind it. But none of the devices got an IP. They all sat with those 169.254.x.x APIPA addresses, basically stuck off the network.

🔍 What I Saw

• Checked show ip dhcp binding → nothing listed.

• Ran debug ip dhcp server packet → saw DISCOVER messages coming in, but no OFFER going out.

• Looked at the config with show run | include dhcp → pool was defined correctly.

Then I dug into the interface config and realized the LAN interface didn’t have the ip helper-address. That’s why the requests weren’t being relayed properly.

✅ What Fixed It

1. Double-checked the DHCP pool:

   Code

   ip dhcp pool BRANCH_POOL
   network 192.168.10.0 255.255.255.0
   default-router 192.168.10.1
   dns-server 8.8.8.8
   

2. Added the helper address:

   Code

   interface GigabitEthernet0/1
   ip helper-address 192.168.10.1
   

3. Made sure no ACLs were blocking DHCP ports (67/68).

4. Cleared bindings to restart fresh:

   Code

   clear ip dhcp binding *
   

After that, clients immediately started pulling IPs. show ip dhcp binding showed active leases, and everything was reachable again.

📌 Lesson Learned

It wasn’t the pool config—it was the missing relay. Easy to overlook, but critical in multi-VLAN or routed setups. DHCP isn’t just about defining ranges; you’ve got to make sure the requests actually get to the server.