IS-IS addressing

OSI uses connectionless network protocol addresses (CNLP)

When CLNP assigned to a router it becomes a Network Service Access Point address (NSAP)
or Net address

NSAP address can be up to 20 bytes

Original OSI implementation defines 5 fields in NSAP

Cisco implementation defines 3 fields:
1) The Area address
2)The system ID
3)The NSAP selector (NSEL)

NSEL - всегда 00, просто определяет, что это IS система.
System ID - всегда 6 байт. Идентификатор роутера. Должен быть уникален
Остальное - Area address

EX: 49.0003.4444.4444.4444.00

49.0003 - Area id

4444.4444.4444 - System ID

Best practice: System ID = Router MAC