Configure OSPF Inter-Area Filtering

ABR type 3 LSA filtering extends the capability of an ABR that is running OSPF to filter type 3 LSAs between different OSPF areas. Once a prefix list is configured, only the specified prefixes are sent from one OSPF area to another OSPF area. All other prefixes are restricted to their OSPF area. You can apply this type of area filtering to traffic going into or coming out of an OSPF area, or to both the incoming and outgoing traffic for that area.

When multiple entries of a prefix list match a given prefix, the entry with the lowest sequence number is used. For efficiency, you may want to put the most common matches or denials near the top of the list by manually assigning them a lower sequence number. By default, sequence numbers are automatically generated in increments of 5, beginning with 5.

Procedure

Step 1

Choose Devices > Device Management, and edit the threat defense device.

Step 2

Click Routing.

Step 3

(For a virtual-router-aware device) From the virtual routers drop-down list, choose the virtual router for which you are configuring OSPF.

Step 4

Click OSPF.

Step 5

Select InterArea > Add.

You can click Edit (edit icon), or use the right-click menu to cut, copy, past, insert, and delete inter-areas.

Step 6

Configure the following inter-area filtering options for each OSPF process:

  • OSPF Process—For a device using virtual routing, the drop-down lists the unique process IDs generated for the selected virtual router.

  • Area ID—The area for which routes are to be summarized.

  • PrefixList—The name of the prefix. To add a new prefix list object, see Step 5.

  • Traffic Direction—Inbound or outbound. Choose Inbound to filter LSAs coming into an OSPF area, or Outbound to filter LSAs coming out of an OSPF area. If you are editing an existing filter entry, you cannot modify this setting.

Step 7

Click Add (add icon), and enter a name for the new prefix list, and whether to allow overrides.

You must configure a prefix list before you can configure a prefix rule.

Step 8

Click Add to configure prefix rules, and configure the following parameters:

  • Action—Select Block or Allow for the redistribution access.

  • Sequence No—The routing sequence number. By default, sequence numbers are automatically generated in increments of 5, beginning with 5.

  • IP Address—Specify the prefix number in the format of IP address/mask length.

  • Min Prefix Length—(Optional) The minimum prefix length.

  • Max Prefix Length—(Optional) The maximum prefix length.

Step 9

Click OK to save the inter-area filtering configuration.

Step 10

Click Save on the Routing page to save your changes.

What to do next

Continue with Configure OSPF Filter Rules.