User Guide

16 Server Communications Administration Guide
Server Communications Administration Guide
103-000145-001
August 30, 2001
Novell Confidential
Manual 99a38 July 17, 2001
IPX Addressing
IPX defines its own internetwork and intranode (or intranetwork) addressing.
For intranode addressing, IPX uses the physical address assigned to the
network board. The IPX network address uniquely identifies an IPX server on
an IPX network and individual processes within the server. A complete IPX
network address is a 12-byte hexadecimal number comprising the following
components:
 A 4-byte network number (server)
 A 6-byte node number (server)
 A 2-byte socket number (server process)
The following is an example of a complete IPX network address:
FEDCBA98 1A2B3C5D7E9F 0453
Each number in an IPX address is contained in a field in the IPX header and
represents a source or destination network, node, or socket. The network
number is used only for network-layer operations, namely routing. The node
number is used for local, or same-segment, packet transmission. The socket
number directs a packet to a process operating within a node.
ARP
Unlike IPX, IP addresses are not the same as the hardware address of the
network board, so there must be a way to discover the physical, or media
access control (MAC) address. The Address Resolution Protocol (ARP)
performs this task. When an IP address is mapped to a MAC address, ARP is
used on broadcast networks such as Ethernet, token ring, and ARCnet. When
a node uses IP to send a packet, it must determine which physical address on
the network corresponds to the destination IP address. To find the physical
address, the node broadcasts an ARP packet containing the destination IP
address. The node with the specified destination IP address sends its physical
address back to the requesting node.To speed packet transmissions and reduce
the number of broadcast requests that must be examined by every node on the
network, each node keeps an address resolution cache, or ARP table. Each
time the node broadcasts an ARP request and receives a response, it creates an
entry in its address resolution cache. The entry maps the IP address to the
physical address. When the node sends an IP packet, it looks up the IP address
in its cache and uses the physical address, if found. The node broadcasts an
ARP request only if the IP address is not in its cache.