3Com MSR 50 Series, Configuration Manual

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940 C
HAPTER
58: OSPF C
ONFIGURATION
n
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An OSPF process ID is unique, including the process ID for OSPF multi-instance,
which cannot be the same as any previously configured ID.
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A network segment can only belong to one area.
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It is recommended to configure a description for each OSPF process to help
identify purposes of processes and for ease of management and memorization.
■
It is recommended to configure a description for each area to help identify
purposes of areas and for ease of management and memorization.
Configuring OSPF
Area Parameters
Splitting an OSPF AS into multiple areas reduces the number of LSAs on networks
and extends OSPF application. For those non-backbone areas residing on the AS
boundary, you can configure them as Stub areas to further reduce the size of
routing tables on routers in these areas and the number of LSAs.
A stub area cannot redistribute routes, thus introducing the concept of NSSA,
where type 7 LSAs (NSSA External LSAs) are advertised. Type 7 LSAs originate from
the ASBR in a NSSA area. When arriving at the ABR in the NSSA area, these LSAs
will be translated into type 5 LSAs for advertisement to other areas.
Non-backbone areas exchange routing information via the backbone area.
Therefore, the backbone and non-backbone areas, including the backbone itself
must maintain connectivity.
If necessary physical links are not available for this connectivity maintenance, you
can configure virtual links to solve it.
Prerequisites Before configuring an OSPF area, you have configured:
■
IP addresses for interfaces, making neighboring nodes accessible with each
other at network layer.
■
OSPF basic functions
Configuration Procedure Follow these steps to configure OSPF area parameters:
To do... Use the command... Remarks
Enter system view system-view -
Enter OSPF view ospf [ process-id | router-id
router-id | vpn-instance
instance-name ] *
-
Enter area view area area-id Required
Configure the area as a stub
area stub [ no-summary ] Optional
Not configured by default
Configure the area as an
NSSA area nssa
[ default-route-advertise |
no-import-route |
no-summary ] *
Optional
Not configured by default
Specify a cost for the default
route advertised to the stub or
NSSA area default-cost cost Optional
Defaults to 1