5. DHCP Configuration - metrafonic/Cisco-Cheatsheet GitHub Wiki

IP relaying of DHCP (IPHELPER)

Challenge I have not managed to figure out how this can be done to request an ip over multiple routers. As of right now i am only able to do this on a router that is connected to both subnets directly. In the topology above, we have one DHCP server in the middle, three relays and three clients, though only two of the relay servers work correctly.

Enable IPHELPER on router

# conf t
(config)# int [interface to relay to]
(config-if)# ip helper [dhcp server address]

Check IPHELPER configuration

# show ip int [interface]

DHCP Server Configuration

Creating the pool

(config)# ip dhcp pool [nameofpool]
(dhcp-config)# network [nettID] [subnet]

Note that the nettID where the client request is coming from will be checked against the nettID and subnet set here. if the two do not match, an address will not be allocated.

(dhcp-config)# default-router [dafault router]
(dhcp-config)# dns-server [dafault dns]
(dhcp-config)# domain-name [example.com]
(dhcp-config)# lease [days]
(dhcp-config)# exit

Excluding Addresses

(config)# ip dhcp excluded-address [start reserved ip] [end reseved ip]

Debugging

View DHCP address leases

# show ip dhcp binding

View DHCP pool statistics

# show ip dhcp server statistics

View DHCP pool settings

# show ip dhcp pool