Defining Areas - Nortel Alteon OS 42C4911 Application Manual

Alteon OS Application Guide

Defining Areas

If you are configuring multiple areas in your OSPF domain, one of the areas must be desig-
nated as area 0, known as the backbone. The backbone is the central OSPF area and is usually
physically connected to all other areas. The areas inject routing information into the backbone
which, in turn, disseminates the information into other areas.
Since the backbone connects the areas in your network, it must be a contiguous area. If the
backbone is partitioned (possibly as a result of joining separate OSPF networks), parts of the
AS will be unreachable, and you will need to configure virtual links to reconnect the parti-
tioned areas (see
Up to three OSPF areas can be connected to the GbE Switch Module with Alteon OS software.
To configure an area, the OSPF number must be defined and then attached to a network inter-
face on the switch. The full process is explained in the following sections.
An OSPF area is defined by assigning two pieces of information—an area index and an area
ID. The command to define an OSPF area is as follows:
>> #
N – The aindex option above is an arbitrary index used only on the switch and does not
OTE
represent the actual OSPF area number. The actual OSPF area number is defined in the
areaid portion of the command as explained in the following sections.
Assigning the Area Index
The aindex <area index> option is actually just an arbitrary index (0-2) used only by the
GbE Switch Module. This index does not necessarily represent the OSPF area number, though
for configuration simplicity, it should where possible.
For example, both of the following sets of commands define OSPF area 0 (the backbone) and
area 1 because that information is held in the area ID portion of the command. However, the
first set of commands is easier to maintain because the arbitrary area indexes agree with the
area IDs:
Area index and area ID agree
/cfg/l3/ospf/aindex 0/areaid 0.0.0.0
/cfg/l3/ospf/aindex 1/areaid 0.0.0.1
Area index set to an arbitrary value
/cfg/l3/ospf/aindex 1/areaid 0.0.0.0
/cfg/l3/ospf/aindex 2/areaid 0.0.0.1
194 Chapter 12: OSPF
"Virtual Links" on page
/cfg/l3/ospf/aindex <area index>/areaid <n.n.n.n>
198).
(Use index 0 to set area 0 in ID octet format)
(Use index 1 to set area 1 in ID octet format)
(Use index 1 to set area 0 in ID octet format)
(Use index 2 to set area 1 in ID octet format)
42C4911, January 2007