3Com 2500 manual Routing with, Classical IP over

4-10 CHAPTER 4: ROUTING WITH IP TECHNOLOGY

Routing with	LANPlex Extended Switching software supports classical IP routing over ATM
Classical IP over	ARP in an ATM network. Classical IP over ATM uses Logical IP Subnets (LISs)
ATM	to forward packets within the network environment.
	See the LANplex® 2500 Operation Guide for detailed information about the
	ATM protocol architecture. See the LANplex® 2500 Administration Console
	User Guide for information about how to configure ATM ports.
About Logical IP	An LIS is a group of IP nodes that belong to the same subnet, and which are
Subnets (LISs)	directly connected to a single ATM network. When you add a node to a LIS
	through the Administration Console IP interface menu, you define its IP
	address, subnet mask, and the address an ATM ARP server that supports it.
ATM ARP Servers	An ATM ARP server maintains a table of IP addresses and their
	corresponding ATM addresses and circuit information. To forward IP
	packets over an ATM interface, the network node learns the ATM address for
	the corresponding IP address from the ATM ARP server.
	Each ATM ARP server supports a single LIS. You can associated two or more
	LISs with the same ATM network, but each LIS operates independently of
	other LISs on the network.

Several types of network nodes can function as ATM ARP servers:

■Any LANplex system with revision 8.1.0 or later of Extended Switching software

■An ATM switch

■A UNIX® workstation

The following sequence describes how the ATM ARP server learns and stores information about the IP and ATM addresses of nodes in the network.

■A node establishes a connection to the ATM ARP server

■The ATM ARP server sends an inverse ATM ARP request to the node, requesting its IP and ATM address

■When the node returns this information, the ATM ARP server stores, or caches, it in the ATM ARP server table.