Chapter 9: AI2524 OSI/CLNP Configuration Steps
August 1997 Page 9-3
2524UM
The area address uniquely identifies the routing area and the system ID
identifies each node.
Figure 9-2:Sample Domainand Area Addresses
The key difference between the ISO IGRP and IS-IS NSAP addressing
schemes is in the definition of area addresses. Both use the system ID
for Level1 routing (routing within an area). However, they differ in
the way addresses are specified for area routing. An ISO IGRP NSAP
address includes three separate fields for routing: the domain, area,
and system ID. An IS-IS address includes two fields: a single contin
uous area fie ld (comprising the domainand area fields) and the system
ID.
ISO IGRP NSAP Address
The ISO IGRP NSAP address is divided into three parts: a
domai npart, an area address, and a system ID. D omainrouting is per-
formed on the doma inpart of the address. Area routing for a given
domai nuses the area address. System routing for a g iven area uses the
system ID part. The NSAP address is laid out as:
zThe domainpart is of variable length and comes before the area
address.
zThe area address is the 2 bytes before the system ID.