Installing and Administering OSI Transport Services

78 Chapter 2
Planning Your Network
Determine the Network Structure
NOTE Information beyond the node name, such as X.25 subaddresses, network
addresses, and applications, can be kept separately by making copies of
the “Remote System Worksheet.” See chapter 4, “Gathering
Configuration Information.”
Determine the Addressing Scheme
Network Address
At this point, you have determined the layout of your network. Now
develop an addressing scheme that facilitates routing in your existing
network, as well as future expansion.
Most network address formats allow you to segment your network into
routing domains and areas. Examine your network map and consider:
• Areas should be defined as groups of subnets that are connected and
have common bandwidth capabilities. For example, if you have two
LAN subnetworks connected by an Intermediate System, you may
consider them to be in the same area.
• Do not assign the same area ID to subnets that are connected to one
another, but differ in bandwidth (for example, an X.25 subnetwork
and a LAN subnetwork, or two LANs connected via a modem link).
• Areas should not contain more than 10,000 nodes. This is dictated by
the IS to IS protocol.
• The assignment of domain identifiers is largely a policy decision. Any
number of areas may be assigned to a single domain. However, a
limitation of 10,000 areas per domain is a good rule.
You may assign a single domain ID to your entire network unless the
following criteria are true.
• Any area that is isolated from another area should have a
different Domain ID.
• If, for security reasons, you wish to distinguish between traffic in
different areas, you should assign different domain IDs to those
areas. For example, could assign “Finance” and “Research”
different domains.