Handbook

N8406-023 1Gb Intelligent L3 Switch Application Guide 112
OSPF implementation
The switch supports a single instance of OSPF and up to 512 routes on the network. The following sections
describe OSPF implementation in the switch:
Configurable Parameters
Defining Areas
Interface Cost
Electing the Designated Router and Backup
Summarizing Routes
Default Routes
Virtual Links
Router ID
Authentication
Configurable parameters
OSPF parameters can be configured through the Command Line Interface (CLI), Browser-Based Interface (BBI) for
the switches, or through SNMP. For more information, see ―Accessing the Switch.‖
The CLI supports the following parameters: interface output cost, interface priority, dead and hello intervals,
retransmission interval, and interface transit delay.
OSPF traps—Traps produce messages upon certain events or error conditions, such as missing a hello, failing a
neighbor, or recalculating the SPF.
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 this 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.