How to Configure DHCP on a Cisco Router
To configure a Cisco router as a DHCP server: exclude any static addresses, create a pool with the network, default gateway and DNS server. Clients then lease addresses automatically.
A Cisco router can hand out IP addresses to a subnet via DHCP. This guide sets up a working pool. Practise in the DHCP lab.
Step 1: Exclude reserved addresses
configure terminalip dhcp excluded-address 192.168.1.1 192.168.1.10 | Keeps .1-.10 free for routers, servers, printers |
Step 2: Create the DHCP pool
ip dhcp pool LANnetwork 192.168.1.0 255.255.255.0 | Defines the addressable range for clients |
Step 3: Set gateway and DNS options
default-router 192.168.1.1dns-server 8.8.8.8 | Handed to clients so they can route out and resolve names |
Verification
Set client PCs to DHCP — they should lease addresses from .11 upward (respecting exclusions). show ip dhcp binding lists each lease with its MAC. For a DHCP server on another subnet, add ip helper-address on the client-side gateway.
Frequently asked questions
How do I configure DHCP on a Cisco router?
Exclude static addresses, then create a pool (ip dhcp pool NAME) specifying the network, default-router and dns-server.
Why exclude addresses before creating the pool?
So statically assigned devices (routers, servers, printers) never conflict with dynamically leased addresses.
How do I verify DHCP is working?
show ip dhcp binding lists active leases; on a client, check it received an address, gateway and DNS from the pool.
How does DHCP work across different subnets?
Configure ip helper-address on the client-facing gateway interface — it relays broadcast DHCP requests to a server on another subnet.
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