Cisco Systems CL-28826-01 General Tab

54-3

User Guide for Cisco Security Manager 4.4

OL-28826-01

Chapter54 Configuring Routing Policies on Firewall Devices

Configuring OSPF

A router that has interfaces in multiple areas is called an Area Border Router (ABR). A router that acts

as a gateway to redistribute traffic between routers using OSPF and routers using other routing protocols

is called an Autonomous System Boundary Router (ASBR).

An ABR uses LSAs to send information about available routes to other OSPF routers. Using ABR type

3 LSA filtering, you can have separate private and public areas with the security appliance acting as an

ABR. Type 3 LSAs (inter-area routes) can be filtered from one area to other. This lets you use NAT and

OSPF together without advertising private networks.

Note Only type 3 LSAs can be filtered. If you configure the security appliance as an ASBR in a private

network, it will send type 5 LSAs describing private networks, which will be broadcast to the entire

autonomous system (AS) including public areas.

If NAT is employed but OSPF is only running in public areas, routes to public networks can be

redistributed inside the private network, either as default or type 5 AS External LSAs. However, you

need to configure static routes for the private networks protected by the security appliance. Also, you

should not mix public and private networks on the same security appliance interface.