3Com 8807 Configuration Manual page 317

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Configuring OSPF Route
Filtering
For an ASBR, the system generates the corresponding Type-5 LSA or Type-7 LSA
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by default when a default route existed in the routing table.
For an ABR, the system will generate a Type-5 LSA or Type-7 LSA no matter
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whether there is a default route in the routing table.
The broadcasting scope of Type-5 LSA or Type-7 LSA advertising the default
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route is the same as that of the common Type-5 LSA or Type-7 LSA.
Perform the following configuration in OSPF view.
Table 278 Configure OSPF to import the default route
Operation
Import the default route to OSPF
Remove the imported default route
By default, OSPF does not import the default route.
If you use the always keyword of this command, the system will generate a
Type-5 or Type-7 LSA no matter whether there is default route in the routing table.
Be cautious that the always keyword is only valid for an ASBR.
Because OSPF does not calculate the LSAs it generated during SPF calculation,
there is no default route in the OSPF route on this router. To ensure the correct
routing information, you should configure to import the default route on the
router only connected to the external network.
After the default-route-advertise command is configured on the OSPF
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router, this router becomes an ASBR. For the OSPF router, the
default-route-advertise and import-route commands have the similar
effect.
For the ABR or ASBR in the NSSA area, the default-route-advertise and nssa
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default-route-advertise commands have the same effect.
Perform the following configuration in OSPF view.
Configuring OSPF to filter the received routes
Table 279 Enable OSPF to filter the received routes
Operation
Disable filtering the received
global routing information
Cancel filtering the received
global routing information
By default, OSPF will not filter the received routing information.
Configuring filtering the routes imported to OSPF
Use the filter-policy export command to configure the ASBR router to filter the
external routes imported to OSPF. This command is only valid for the ASBR router.
Command
default-route-advertise [ always | cost value | type
type-value | route-policy route-policy-name ]*
undo default-route-advertise [ always | cost | type
| route-policy ]*
Command
filter-policy { acl-number | ip-prefix ip-prefix-name | gateway
ip-prefix-name } import
undo filter-policy { acl-number | ip-prefix ip-prefix-name |
gateway ip-prefix-name } import
Configuring OSPF 317