How to configure Cisco Router as DHCP Relay Agent

Asalam o alikum , brothers & sisters, today we will learn How to configure Cisco Router as DHCP Relay Agent.

A DHCP relay agent is any host that forwards DHCP packets between clients and servers. Relay agents are used to forward requests and replies between clients and servers when they are not on the same physical subnet.

When do you need a Relay Agent?

When your DHCP server and clients are on different networks, you need a relay agent to forward DHCP packets from Clients to server and vice versa. Because Router does not forward broadcast packets, so clients in one subnet will not be able to get IP addresses from DHCP Server in another subnet.

In our lab scenario , we have a Router with 2 networks attached to it (192.168.10.0/24 and 192.168.11.0/24). We have a DHCP Server connected in the 192.168.11.0/24 subnet , with IP 192.68.11.6. and 2 PC’s attached, 1 in each subnet

first step is to establish connectivity between all devices. next we will configure DHCP Server .

in DHCP server we will configure 2 pools(192.168.10.0/24 & 192.168.11.0/24) with range of 100 hosts in each subnet.

When we start DHCP services, you will notice that PC’s in 11.0/24 will auto assign IP using DHCP, but PC’s in 10.0/24 will fail.

next step is to configure relay agent on Router .

Run command “ip helper-address 192.168.11.6” on interface connected to 10.0/24 subnet.

(config)#int g0/0

(config-if)#ip helper-address 192.168.11.6

after this step you will notice that , now PC’s in 10.0/24 subnet will also obtain IP Address via DHCP