An IS-IS router has been assigned the NSAP address: 49.00F0.0100.5012.3010.00. What is the Area ID to which the router belongs?

The IS-IS Network Service Access Point (NSAP) address is structured into three parts: the Area ID, the System ID, and the N-Selector (NSEL). According to the ISO/IEC 10589 standard, the NSEL is the last byte (octet), and the System ID is a fixed length of six bytes that precedes the NSEL. The remainder of the address at the beginning constitutes the Area ID.

Given the address 49.00F0.0100.5012.3010.00:

NSEL: 00 (the last byte)

System ID: 0100.5012.3010 (the preceding six bytes)

Area ID: 49.00F0 (the remaining part)

B. 49.00F0.0100: This is incorrect because it would imply the System ID is only four bytes long (5012.3010), which violates the standard six-byte length for a router's System ID.

C. 5012.3010.00: This is incorrect as it represents the last four bytes of the System ID combined with the one-byte NSEL, not the Area ID.

D. 00F0 0100: This is incorrect as it is a fragment containing parts of both the Area ID (00F0) and the System ID (0100).

1. Medhi

D.

& Ramasamy

K. (2017). Network Routing: Algorithms

Protocols

and Architectures (2nd ed.). Morgan Kaufmann.

Reference: Chapter 5

Section 5.4.1

"Addressing in an OSI Environment

" describes the NSAP address format used by IS-IS. It specifies that the System ID is a 6-byte identifier and the NSEL is a 1-byte field

with the variable-length Area ID preceding them.

2. ISO/IEC 10589:2002

"Information technology -- Telecommunications and information exchange between systems -- Intermediate System to Intermediate System intra-domain routeing information exchange protocol..."

Reference: Section 7.4

"NSAP addresses

" defines the components of the NSAP address. It specifies that the System ID field has a fixed length throughout a routing domain (conventionally 6 octets) and is followed by a single octet NSEL.

3. Ericsson IP Operating System (IPOS) Software

Command Reference.

Reference: In the documentation for the router isis command set

the net command syntax is defined as area-id.system-id.sel. Examples provided

such as net 49.0001.0000.0000.1001.00

consistently show a 6-byte System ID (0000.0000.1001)

reinforcing the standard structure.