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950 PowerConnect B-Series FCX Configuration Guide
53-1002266-01
Configuring OSPF
29
Preventing specific OSPF routes from being installed in the IP route
table
By default, all OSPF routes in the OSPF route table are eligible for installation in the IP route table.
You can configure a distribution list to explicitly deny specific routes from being eligible for
installation in the IP route table.
NOTE
This feature does not block receipt of LSAs for the denied routes. The Layer 3 Switch still receives
the routes and installs them in the OSPF database. The feature only prevents the software from
installing the denied OSPF routes into the IP route table.
To configure an OSPF distribution list:
• Configure a standard or extended ACL that identifies the routes you want to deny. Using a
standard ACL lets you deny routes based on the destination network, but does not filter based
on the network mask. To also filter based on the destination network network mask, use an
extended ACL.
• Configure an OSPF distribution list that uses the ACL as input.
NOTE
If you change the ACL after you configure the OSPF distribution list, you must clear the IP route table
to place the changed ACL into effect. To clear the IP route table, enter the clear ip route command
at the Privileged EXEC level of the CLI.
The following sections show how to use the CLI to configure an OSPF distribution list. Separate
examples are provided for standard and extended ACLs.
NOTE
The examples show named ACLs. However, you also can use a numbered ACL as input to the OSPF
distribution list.
Using a standard ACL as input to the distribution list
To use a standard ACL to configure an OSPF distribution list for denying specific routes, enter
commands such as the following.
PowerConnect(config)#ip access-list standard no_ip
PowerConnect(config-std-nACL)#deny 4.0.0.0 0.255.255.255
PowerConnect(config-std-nACL)#permit any any
PowerConnect(config-std-nACL)#exit
PowerConnect(config)#router ospf
PowerConnect(config-ospf-router)#distribute-list no_ip in
The first three commands configure a standard ACL that denies routes to any 4.x.x.x destination
network and allows all other routes for eligibility to be installed in the IP route table. The last three
commands change the CLI to the OSPF configuration level and configure an OSPF distribution list
that uses the ACL as input. The distribution list prevents routes to any 4.x.x.x destination network
from entering the IP route table. The distribution list does not prevent the routes from entering the
OSPF database.
Syntax: [no] distribute-list <ACL-name> | <ACL-id> in [<interface type>] [<interface number>]
Syntax: [no] ip access-list standard <ACL-name> | <ACL-id>