How to filter OSPF Routes
Description
OSPF Route filtering is a method for selectively identifying routes that are advertised or received from neighbor routers.
There are 2 methods of filtering routes in OSPF.
- Filter routes on ABR using "filter-list"
This method filters the Inter-Area (IA) routes as they are coming from one area and going into another area
- Filter routes on a local router using "distribute-list".
This method filters out any OSPF route (O, IA, E) from being added to the routing table of a local router within an area
Resolution
Filtering Routes on ABR:
admin@SonicWall> conf
config(SonicWall)# routing
(config-routing)# ospf
ARS OSPF>conf t
ARS OSPF(config)>ip prefix-list Filter-Routes seq 10 deny < Subnet/M >
ARS OSPF(config)>ip prefix-list Filter-Routes seq 20 permit any
ARS OSPF(config)>router ospf
ARS OSPF(config-router)>area 0 filter-list prefix Filter-Routes in
ARS OSPF(config-router)>exit
ARS OSPF(config)>exit
ARS OSPF>write file
Filtering Routes on an OSPF router:
admin@SonicWall> conf
config(SonicWall)# routing
(config-routing)# ospf
ARS OSPF>conf t
ARS OSPF(config)>access-list Filter-Routes deny < Subnet/M >
ARS OSPF(config)>access-list Filter-Routes permit any
ARS OSPF(config)>router ospf
ARS OSPF(config-router)>distribute-list Filter-Routes in
ARS OSPF(config-router)>exit
ARS OSPF(config)>exit
ARS OSPF>write file
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