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Dell PowerEdge FN I/O Module Configuration Guide 9.10(0.0)

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IS-IS Addressing

IS-IS PDUs require ISO-style addressing called network entity title (NET).

For those familiar with name-to-network service mapping point (NSAP) addresses, the composition of the NET is identical to an NSAP address, except the last byte is always 0. The NET is composed of the IS-IS area address, system ID, and N-selector. The last byte is the N-selector. All routers within an area have the same area portion. Level 1 routers route based on the system address portion of the address, while the Level 2 routers route based on the area address.
The NET length is variable, with a maximum of 20 bytes and a minimum of 8 bytes. It is composed of the following:
  • area address — within your routing domain or area, each area must have a unique area value. The first byte is called the authority and format indicator (AFI).
  • system address — the router’s MAC address.
  • N-selector — this is always 0.
The following illustration is an example of the ISO-style address to show the address format IS-IS uses. In this example, the first five bytes (47.0005.0001) are the area address. The system portion is 000c.000a.4321 and the last byte is always 0.
Figure 1. ISO Address Format Illustration of the ISO address format.

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