HP 200 Series Services And Applications page 116

Internet Protocol Routing Service
IP Routing Decisions
IP Routing Decisions
IP routing decisions are based upon the destination network-layer address
contained in each data packet that is traveling through the IP network. The
most significant bits of the address identify the destination subnetwork,
while the least significant bits identify a specific node (host, router, HP
managed hub, HP managed bridge, etc.) on that subnetwork. The subnet
mask is used to distinguish these parts of the 32-bit IP address.
In figure 2, the subnet mask 255.255.255.0 determines that the most signifi-
cant 24 bits of each IP address will identify the subnetwork, leaving 8 bits on
each subnetwork to identify individual hosts and router interfaces. All
addresses will be of the form 128.1.sss.hhh, where "sss" is a number (1–254)
identifying the subnetwork and "hhh" is a number (1254) identifying a node
(host) on that subnetwork. Note that each port (network interface) on the
router resides on a different subnetwork and requires a unique IP address.
For more information on IP addressing, refer to the student workbook in the
HP course "HP Internet Routing Products", or to the reference manual for
the HP routers.
The router bases IP packet-routing decisions on the following:
The network and subnetwork portion of the destination IP address
contained in each packet.
The information it has about the network's topology. This topology
information is maintained in the "IP routing table".
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