Here is an example of a PAP structure that may either be used with a current
allocation format that allows the PAP to be defined (such as ANSI), or with a
temporary AP.
The last portion of the PAP should have the following structure:
The above PAP allocation follows the structure used by the IS-IS protocol. It
allows areas to be created that contain multiple subnetworks.
The User Defined portion may be comprised of one or more of the following
fields:
A version or DSP format identifier. This allows the format of the PAP to be
redefined at some later point in time. These fields are usually two octets in length,
but any size may be chosen. For most NSAP spaces, one octet will often be
sufficient.
A reserved field. It is often a good idea to reserve a few octets of space for future
use.
If any of these fields are used, they should be defined in the order, left to
right in the PAP, as they are listed above.
Network Identifiers (Network ID) |
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Because of the hierarchical definition of NSAP formats, a prefix portion of
an NSAP may be used to identify a group of systems that reside in the same
routing domain, the same area, or the same subnetwork. This prefix portion
is called an "NSAP Prefix," or a "Network ID."
As an example, suppose Joe's Grommet Shop, whose AP value is
39840F010101, decides to use the Recommendation 1 format for its PAP.
It has two areas in routing domain 0000 that are assigned Area ID values:
0001 and 0002. The corresponding Network IDs for these areas are:
39840F01010100000001 and 39840F01010100000002.
Network IDs may be used in OTS to simplify the configuration of routing
information. Rather than configuring a route to every remote system, OTS
allows network administrators to configure a route to a distant routing
domain, area, or subnetwork by using its Network ID. It also allows local
subnetworks to have their Network IDs configured to help the routing
protocols with local network traffic.
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