Defining Areas; Assigning The Area Index - HP 438031-B21 - 1:10Gb Ethernet BL-c Switch Application Manual

In addition to the above parameters, you can also specify the following:
Link-State Database size—The size of the external LSA database can be specified to help manage
the memory resources on the switch.
Shortest Path First (SPF) interval—Time interval between successive calculations of the shortest path
tree using the Dijkstra's algorithm.
Stub area metric—A stub area can be configured to send a numeric metric value such that all routes
received via that stub area carry the configured metric to potentially influence routing decisions.
Default routes—Default routes with weight metrics can be manually injected into transit areas. This
helps establish a preferred route when multiple routing devices exist between two areas. It also helps
route traffic to external networks.

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").
Up to three OSPF areas can be connected to the HP 1:10GbE switch. 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
command to define an OSPF area is as follows:
>> # /cfg/l3/ospf/aindex <area index>/areaid <n.n.n.n>
NOTE: The aindex 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 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 switch. 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 (Use index 0 to set area 0 in ID octet format)
/cfg/l3/ospf/aindex 1/areaid 0.0.0.1 (Use index 1 to set area 1 in ID octet format)
Area index set to an arbitrary value
/cfg/l3/ospf/aindex 1/areaid 0.0.0.0 (Use index 1 to set area 0 in ID octet format)
/cfg/l3/ospf/aindex 2/areaid 0.0.0.1 (Use index 2 to set area 1 in ID octet format)
OSPF
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