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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 Domain and 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 Level 1 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 field (comprising the doma inand 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 given area uses the
system ID part. The NSAP address is laid out as:
z
The domai npart is of variable length and comes before the area
address.
z
The area address is the 2 bytes before the system ID.