AIS AI2524 user manual 4IS-IS Nsap Addressing Structure Addressing Rules

Chapter 9: AI2524 OSI/CLNP Configuration Steps

The IS-IS routing protocol interprets the bytes from the AFI up to (but not including) the system ID field in the DSP as an area identifier. Th system ID specifies the system.

Figure 9-4 illustrates the IS-IS NSAP addressing structure. The maxi- mum address size is 20 bytes.

Figure 9-4:IS-IS NSAP Addressing Structure

Addressing Rules

All NSAP addresses must obey these constraints:

zNo two nodes can have addresses with the same NET; that is, ad- dresses that match all but the N-selector (S) field in the DSP.

zNo two nodes residing within the same area can have addresses in which the system ID fields are the same.

zISO IGRP requires at least 10 bytes of length: 1 byte for domain, 2 bytes for area, 6 bytes for system ID, and 1 byte for N-selector.

zISO IGRP and IS-IS should not be configured for the same area. Do not specify an NSAP address where all bytes up to (but not in- cluding) the system ID are the same when enabling both ISO IGRP and IS-IS routing.

zA router can have one or more area addresses. The concept of mul- tiple area addresses is described in Assign Multiple Area Address- es to IS-IS Areas.

zIS-IS requires at least 8 bytes: one byte for area, 6 bytes for system ID, and 1 byte for N-selector.

August 1997	Page 9-5
2524UM