DHCP Relay Application Notes
DHCP Relay Application Notes
The following are application notes for DHCP relay:
•The IP address in the Internal profile must be on the same network as that of the DHCP clients.
•A firewall configuration (where there is an Internal profile and LAN IP address) does not work with DHCP relay.
•A configuration where PAT is on and DHCP relay is enabled is not valid. DHCP relay will attempt to cross from a public to a private domain. PAT prevents access to the private domain. DHCP relay fails because it must reference the router’s private address.
•DHCP relay and DHCP server are mutually exclusive. The Cisco 700 series router can function as one or the other, but not both.
PAT Description
Cisco 700 series routers provide PAT, enabling local hosts on a private IP network to communicate externally.
Packets destined for an external address have their private IP address plus port number translated to the router’s external IP address before the IP packet is forwarded to the WAN. IP packets returning to the router have their external IP addresses (plus port number) translated back to the private IP addresses, and the packets are forwarded to the LAN.
When PAT is enabled, the transmission of RIP packets is automatically disabled to prevent a broadcast of the private IP addresses externally.
PAT Application Notes
A configuration where PAT is on and DHCP relay is enabled is not valid. DHCP relay will attempt to cross from a public to a private domain. PAT prevents access to the private domain. DHCP relay fails because it must reference the router’s private address.
Configuring DHCP Relay, DHCP Server, and PAT