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BLADEOS 6.5.2 Application Guide
BMD00220, October 2010 Chapter 20: OSPF 279
Defining Areas
If you are configuring multiple areas in your OSPF domain, one of the areas must be designated 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 partitioned areas
(see “Virtual Links” on page 283).
Up to six OSPF areas can be connected to the G8124 with BLADEOS software. To configure an
area, the OSPF number must be defined and then attached to a network interface 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
commands to define and enable an OSPF area are as follows:
Note – The area option above is an arbitrary index used only on the switch and does not represent
the actual OSPF area number. The actual OSPF area number is defined in the area portion of the
command as explained in the following sections.
Assigning the Area Index
The area <area index> option is actually just an arbitrary index (0–5) used only by the G8124.
This index number 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
area 0 area-id 0.0.0.0 (Use index 0 to set area 0 in ID octet format)
area 1 area-id 0.0.0.1 (Use index 1 to set area 1 in ID octet format)
Area index set to an arbitrary value
area 1 area-id 0.0.0.0 (Use index 1 to set area 0 in ID octet format)
area 2 area-id 0.0.0.1 (Use index 2 to set area 1 in ID octet format)
RS G8124(config)# router ospf
RS G8124(config-router-ospf)# area
<area index> area-id <n.n.n.n>
RS G8124(config-router-ospf)# area <area index> enable
RS G8124(config-router-ospf)# exit