HP HPE FlexNetwork 7500 series, Configuration Manual

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Figure 35 NSAP address format
Area address
The area address comprises the IDP and the HO-DSP of the DSP, which identify the area and the
routing domain. Different routing domains cannot have the same area address.
Typically, a router only needs one area address, and all nodes in the same area must have the same
area address. To support smooth area merging, partitioning, and switching, a router can have a
maximum of three area addresses.
System ID
A system ID uniquely identifies a host or router. It has a fixed length of 48 bits (6 bytes).
The system ID of a device can be generated from the router ID. For example, suppose a router uses
the IP address 168.10.1.1 of Loopback 0 as the router ID. The system ID can be obtained in the
following steps:
1. Extend each decimal number of the IP address to three digits by adding 0s from the left, such as
168.010.001.001.
2. Divide the extended IP address into three sections that each has four digits to get the system ID
1680.1000.1001.
If you use other methods to define a system ID, make sure that it can uniquely identify the host or
router.
SEL
The N-SEL, or the NSAP selector (SEL), is similar to the protocol identifier in IP. Different transport
layer protocols correspond to different SELs. All SELs in IP are 00.
Routing method
The IS-IS address format identifies the area, so a Level-1 router can easily identify packets destined
to other areas. IS-IS routers perform routing as follows:
•
A Level-1 router performs intra-area routing according to the system ID. If the destination
address of a packet does not belong to the local area, the Level-1 router forwards it to the
nearest Level-1-2 router.
•
A Level-2 router performs inter-area routing according to the area address.
NET
A network entity title (NET) identifies the network layer information of an IS. It does not include
transport layer information. A NET is a special NSAP address with the SEL being 0. The length of a
NET is in the range of 8 to 20 bytes, same as a NSAP address.
A NET includes the following parts:
•
Area ID —Has a length of 1 to 13 bytes.
•
System ID —A system ID uniquely identifies a host or router in the area and has a fixed length
of 6 bytes.
•
SEL —Has a value of 0 and a fixed length of 1 byte.
For example, for a NET ab.cdef.1234.5678.9abc.00, the area ID is ab.cdef, the system ID is
1234.5678.9abc, and the SEL is 00.
AFI IDI HO-DSP System ID (6 octet) SEL (1 octet)
IDP
DSP
Area address