BSCI Exam Cram™ 2 (Exam 642-801)

Developing an Effective Addressing Plan for IS-IS Deployment

Integrated IS-IS implements a CLNP node-based address structure to identify routers (even within pure IP environments). These CLNP addresses are called Network Service Access Points (NSAPs) and comprise three components: an area identifier (area ID) prefix, followed by a system identifier (SysID), and an N-selector, as shown in Table 6.3.

Table 6.3. The NSAP Addressing Structure

IDP		DSP
AFI	IDI	High Order DSP	SysID (6 bytes)	NSEL (1 byte)

The NSAP address shown in Table 6.3 is like a combination of an IP address and the upper-layer protocol in the IP header. The following list explains the different elements:

• AFI— This is the 1-byte authority and format ID that designates the formatting as ...