Cisco Systems 3560 사용자 설명서

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. 

You can control interface-specific handling of IP by using address resolution. A device using 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 under Documentation > Cisco IOS Software > 12.2 Mainline > Configuration Guides 
from the Cisco.com page.

You can perform these tasks to configure address resolution:

Verify your entry.

(Optional) Save your entry in the configuration file.