Cisco IE 4000, Software Configuration Manual

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804
Configuring IP Unicast Routing
Configuring IP Addressing

Address Resolution Protocol (ARP) is used to associate IP address with MAC addresses. Taking an IP address as
input, ARP learns the associated MAC address and then stores the IP address/MAC address association in an ARP
cache for rapid retrieval. Then the IP datagram is encapsulated in a link-layer frame and sent over the network.
Encapsulation of IP datagrams and ARP requests or replies on IEEE 802 networks other than Ethernet is specified by
the Subnetwork Access Protocol (SNAP).

Proxy ARP helps hosts with no routing tables learn the MAC addresses of hosts on other networks or subnets. If the
switch (router) receives an ARP request for a host that is not on the same interface as the ARP request sender, and
if the router has all of its routes to the host through other interfaces, it generates a proxy ARP packet giving its own
local data link address. The host that sent the ARP request then sends its packets to the router, which forwards them
to the intended host.
The switch also uses the Reverse Address Resolution Protocol (RARP), which functions the same as ARP does, except
that the RARP packets request an IP address instead of a local MAC address. Using RARP requires a RARP server on the
same network segment as the router interface. Use the
ip rarp-server address interface configuration command to
identify the server.
For more information on RARP, see IP Addressing: ARP Configuration Guide, Cisco IOS Release 15M&T .
You can perform these tasks to configure address resolution:

Defining a Static ARP Cache, page 804

Setting ARP Encapsulation, page 805

Enabling Proxy ARP, page 806
Defining a Static ARP Cache
ARP and other address resolution protocols provide dynamic mapping between IP addresses and MAC addresses.
Because most hosts support dynamic address resolution, you usually do not need to specify static ARP cache entries. If
you must define a static ARP cache entry, you can do so globally, which installs a permanent entry in the ARP cache that
the switch uses to translate IP addresses into MAC addresses. Optionally, you can also specify that the switch respond
to ARP requests as if it were the owner of the specified IP address. If you do not want the ARP entry to be permanent,
you can specify a timeout period for the ARP entry.
BEFORE YOU BEGIN
Review the Configuring Address Resolution Methods, page 803 .