Is-Is Address Structure - H3C S7500 Series Operation Manual

Operation Manual – Routing Protocol
H3C S7500 Series Ethernet Switches
Area 2
L1
Figure 5-2 An example of the IS-IS topology II
Note:
The IS-IS backbone does not need to be a particular Area.
In IS-IS, SPF algorithm is used to generate the shortest path tree (SPT) regardless of
the Level-1 or Level-2 router.

5.1.3 IS-IS Address Structure

I. Address structure
1) NSAP
The ISO uses the NSAP address format shown in
consists of the initial domain part (IDP) and the domain specific part (DSP). The IDP
equals to the network id field in the IP address, and the DSP equals to the subnet and
host id field.
The IDP, defined by OSI, includes the authority and format identifier (AFI) and the
initial domain identifier (IDI).
The DSP includes the high order DSP (HODSP), the System ID and SEL, where the
HODSP identifies the area, the System ID identifies the host, and the SEL indicates
the type of service.
The length of IDP and DSP is variable. The maximum length of the NSAP address is
20 bytes.
Area 1
L1
L1/L2
L2
L2
Area 4
L1/L2
L1
Area 3
Figure
5-4
Chapter 5 IS-IS Configuration
5-3. The NSAP address