Overview

You can configure a bridged IP interface to manage IP packets that are encapsulated inside an Ethernet frame running over a permanent virtual circuit (PVC).

When you configure a bridged IP interface, it automatically performs proxy Address Resolution Protocol (ARP). You can also configure the router as a relay agent that forwards Dynamic Host Configuration Protocol (DHCP) broadcasts.

Proxy ARP

Proxy ARP allows your router to respond to ARP requests on behalf of an Ethernet end node.

The router performs proxy ARP for the ARP requests that come in over the bridged IP interface when both of the following conditions are met:

• The IP address in the ARP request matches an entry in the routing table.
• The route is on a different interface than the one on which the router received the ARP request.

If you specify that the bridged IP interface performs unrestricted proxy ARP, it also performs proxy ARP when the route is on the interface that received the ARP request.

In most situations, do not configure the router to perform unrestricted proxy ARP. Do so for special situations, such as when cable modems are used. When an IP client broadcasts the ARP request across the Ethernet wire, the end node with the correct IP address responds to the ARP request and provides the correct MAC address. If the unrestricted proxy ARP feature is enabled, the router response is redundant and might fool the IP client into determining that the destination MAC address within its own subnet is the same as the address of the router.

DHCP

DHCP provides a mechanism through which hosts using TCP/IP can obtain protocol configuration parameters automatically from a DHCP server on the network.

The most important configuration parameter carried by DHCP is the IP address. A host must be initially assigned a specific IP address that is appropriate to the network to which the computer is attached, and that is not assigned to any other host on that network. If you move a host to a new network, you must give it a new IP address.

DHCP also carries other important configuration parameters such as the subnet mask, default router, and Domain Name System (DNS) server.

An IP client contacts a DHCP server for configuration parameters. The DHCP server is typically centrally located and operated by the network administrator. Because a network administrator manages the server, DHCP clients can obtain reliable parameters appropriate to the current network architecture.

For information about DHCP, see DHCP Overview Information.