AIS AI2524 user manual 3ISO Igrp Nsap Addressing Structure IS-IS Nsap Address

AI2524 Router Card User’s Manual

zThe system ID is the 6 bytes before the N-selector.

zThe N-selector (S) is the last byte of the NSAP address.

Cisco's ISO IGRP routing implementation interprets the bytes from the AFI up to (but not including) the area field in the DSP as domai nidentifier. The area field specifies the area, and the system ID specifies the system.

Figure 9-3 illustrates the ISO IGRP NSAP addressing structure. The maximum address size is 20 bytes.

Figure 9-3:ISO IGRP NSAP Addressing Structure

IS-IS NSAP Address

An IS-IS NSAP address is divided into two parts: an area address and a system ID. Level 2 routing (routing between areas) uses the area ad- dress. Leve l1 routing (routing within an area) uses the system ID ad- dress. The NSAP address is laid out as:

zThe area address is the NSAP address, not including the system ID and N-selector.

zThe system ID is found between the area address and the N-selec- tor byte.

zThe N-selector (S) is the last byte of the NSAP address.

Page 9-4	August 1997
	2524UM