AIS AI2524 user manual 2Sample Domain and Area Addresses, ISO Igrp Nsap Address

Chapter 9: AI2524 OSI/CLNP Configuration Steps

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:

zThe domai npart is of variable length and comes before the area address.

zThe area address is the 2 bytes before the system ID.

August 1997	Page 9-3
2524UM