3Com 3C840 manual IP Routing, Information the router uses to make these assessments is

IP Routing A-9

Once the packet is received by the Router A, attached to LAN 1, it strips off the network header (refer to Figure above) and examines the Layer 3 header information. It then reviews its routing tables in order to establish where to forward the data packet. It is possible that the LAN 1 router has multiple outgoing ports that would allow different transmission routes to the destination network. In our example using Figure A-3, a packet could go via Router D to get to Router B, or it could go more directly across a single direct link between Router A and Router B.

	Figure A–5Data Packet Containing Hardware and Software Addresses
IP Routing	The local router contains, within its routing table, information that will
	allow it to determine the best data transmission route. The type of
	information the router uses to make these assessments is
	protocol-dependent, and some communications protocols may employ a
	range of routing algorithms, and accompanying routing protocols. In the
	case of the TCP/IP protocol suite, the OfficeConnect Remote 840 utilizes
	RIP. RIP is also known as a distance vector protocol.
	Different protocols use different networking characteristics or metrics
	when making routing decisions. The metric employed by RIP is a hop
	count. A hop count is defined by the number of routing nodes there are
	between the source and destination units. In our example, there are two
	hops between LAN 1 and LAN 2 going via Routers A and B. If traffic was
	directed via Routers A,D, and then B, this would be three hops.