IS-IS Network Design Solutions

NSAP Format

NSAP addresses are not fixed in length and can be up to 160 bits (20 bytes) long compared to the fixed 32 bits (4 bytes) of IP addresses. ISO 8348/AD2 specifies a hierarchical scheme for defining global and public NSAP addresses. The following are the seven top-level addressing domains:

• X.121— International plan for public data networks

• ISO DCC— Data Country Code

• F.69— Telex

• E.163— Public Switched Telephone Network

• E.164— ISDN

• ISO 6523— International Code Designator (ICD) for organizations

• Local— For local use only within network domain

Even though format details differ for each top-level domain, all NSAP addresses conform to the generic format shown in Figure 4-3.

Figure 4-3. NSAP address format.

The NSAP format shows two main components: ...