Chapter 4 Is-Is Configuration; Figure 4-2 Nsap Address Architecture - Zte ZXR10 5900E Series Configuration Manual

The relation that can be established between routers is as follows:
L1 neighbor relation can be established between two L1 routers only when the
à
area IDs of them match each other.
L2 neighbor relation can be established between two L2 routers even if the area
à
IDs do not match each other.
L1 neighbor relation can be established between one L1 router and one L1/L2
à
router only when the area IDs of them match each other.
L2 neighbor relation can be established between one L2 router and one L1/L2
à
router even if the area IDs of the routers do not match each other.
L1 neighbor relation and L2 neighbor relation can be established between two
à
L1/L2 routers at the same time if the area IDs of them match each other.
L2 neighbor relation can be established between two L1/L2 routers if the ares IDs
à
of them do not match each other.
l
IS-IS address architecture
ISO address is a network address. It is used to indicate the area ID and the system ID.
The NET address format can be expanded. The system ID usually consists 6 bytes.
It is used to identify the interface MAC address.
NSAP
see Figure
similar to the subnet ID, host address, and the port in an IP address.

Figure 4-2 NSAP Address Architecture

The IDP is defined by the ISO. It consists of the Authority and Format Identifier (AFI)
and the Initial Domain Identifier (IDI). AFI refers to the address allocation organization
and the address format. The IDI is used to identify the domain.
The DSP consists of the High Order DSP, SystemID and the SEL.
The HODSP is used to divide areas.
à
The system ID is used to distinguish hosts.
à
The SEL is used to indicate service type.
à
The length of the IDP and the DSP can be changed. The NSAP can be up to 20 bytes
in length and at least 8 bytes. The system ID identifies a unique host or a router in an
area. Its length is 48 bit (6 bytes) invariably. The SEL (NSAP Selector, sometimes it is
SJ-20150114102049-003|2015-01-15 (R1.0)
consists of the Initial Domain Part (IDP) and the Domain Specific Part (DSP),
4-2. The IDP is similar to the network ID in an IP address, and the DSP is
4-3
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Chapter 4 IS-IS Configuration