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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
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Chapter 35 Configuring IP Unicast Routing
Configuring IP Addressing
To restore the default and have the switch forward packets destined for a subnet of a network with no
network default route to the best supernet route possible, use the ip classless global configuration
command.
Configuring Address Resolution Methods
You can control interface-specific handling of IP by using address resolution. A device usin g IP can have
both a local address or MAC address, which uniquely defines the device on its local segment or LAN,
and a network address, which identifies the network to which the device belongs.
The local address or MAC address is known as a data link address because it is contained in the data link
layer (Layer 2) section of the packet header and is read by data link (Layer 2) devices. To communicate
with a device on Ethernet, the software must learn the MAC address of the device. The process of
learning the MAC address from an IP address is called address resolution. The process of learning the
IP address from the MAC address is called reverse address resolution.
The switch can use these forms of address resolution:
• 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 the Cisco IOS Configuration Fundamentals Configuration Guide,
Release 12.2.
You can perform these tasks to configure address resolution:
• Define a Static ARP Cache, page 35-8
• Set ARP Encapsulation, page 35-10
• Enable Proxy ARP, page 35-10

Define 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
Step 4 show running-config Verify your entry.
Step 5 copy running-config startup-config (Optional) Save your entry in the configuration file.
Command Purpose