3Com Switch 7750 Configuration Guide Guide

296 CHAPTER 34: OSPF CONFIGURATION
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■ The undo protocol multicast-mac enable command must be configured if
Layer 2/Layer 3 multicast function is enabled in the system.
■ The ID of an OSPF process or OSPF multi-instance is unique. That is, the ID of
OSPF multi-instance must be different from any in-use process ID.
■ One segment can belong to only one area and you must specify each OSPF
interface to belong to a particular area.
OSPF Area Attribute
Configuration
Area partition in OSPF reduces the number of LSAs in the network and enhances
OSPF scalability. To further reduce routing table size and the number of LSAs in
some non-backbone areas on the edge of the AS, you can configure these areas as
stub areas.
A stub area cannot import any external route. For this reason the concept of NSSA
area is introduced. Type7 LSAs can be advertised in an NSSA area. Type7 LSAs are
generated by ASBRs of the NSSA area, and will be transformed into AS-external
LSAs whey reaching ABRs in the NSSA area, which will then be advertised to other
areas.
After area partition, the OSPF route updates between non-backbone areas are
exchanged by way of the backbone area. Therefore, OSPF requires that all the
non-backbone areas should keep connectivity with the backbone area and the
backbone area must keep connectivity in itself.
If the physical connectivity cannot be ensured due to various restrictions, you can
configure OSPF virtual links to satisfy this requirement.
Configuration
Prerequisites
Before configuring OSPF area attributes, perform the following tasks:
■ Configuring the network layer addresses of interfaces so that the adjacent
nodes are reachable to each other at the network layer
■ Performing basic OSPF configuration
Configure the router ID router id router-id
Optional
If multiple OSPF processes run
on a router, you are
recommended to use the
router-id keyword in the
following command to specify
different router IDs for
different processes.
Enable OSPF and enter OSPF
view
ospf [ process-id [ router-id
router-id ] ]
Required
Enter OSPF view.
Enter OSPF area view area area-id Required
Configure the network
segments in the area
network address
wildcard-mask
Required
By default, an interface does
not belong to any area.
Table 213 Basic OSPF configuration
Operation Command Description