What is OSPF filtering?
What is OSPF filtering?
The OSPF Inbound Filtering Using Route Maps with a Distribute List feature allows users to define a route map to prevent Open Shortest Path First (OSPF) routes from being added to the routing table. In the route map, the user can match on any attribute of the OSPF route.
What is intra area in OSPF?
Intra Area routes are the “O” routes that you see in the routing table. These routes are routes that are in the same area. Inter-area routes are the “O IA” routes that are learned in different areas.
Can I use the distribute list in out command with OSPF to filter routes?
OSPF routes cannot be filtered from entering the OSPF database. The command distribute-list out works only on the routes being redistributed by the ASBR into OSPF. It can be applied to external type 2 and external type 1 routes but not to intra-area and interarea routes.
How does OSPF choose routes?
If there are multiple routes to a network with the same route type, the OSPF metric calculated as cost based on the bandwidth is used for selecting the best route. The route with the lowest value for cost is chosen as the best route.
What is prefix suppression in OSPF?
An OSPF interface by default advertises all its prefixes in LSAs. You can suppress interfaces from advertising all its prefixes to speed up OSPF convergence. This function also helps improve the network security by preventing IP routing toward the suppressed networks.
Is OSPF intra or inter?
Both Intra and Inter-Area routes are also called OSPF Internal routes, as they are generated by OSPF itself, when an interface is covered with the OSPF network command.
How do you prioritize a route in OSPF?
Setting a Priority for OSPF Routes
- Run system-view. The system view is displayed.
- Run ospf [ process-id ] The OSPF process view is displayed.
- Run preference [ ase ] { preference | route-policy route-policy-name } * A priority is set for OSPF routes. The parameter ase specifies a priority for AS external routes.
Which command is used to apply a distribute list to OSPF?
To enable inbound filtering for routes and define the conditions for distributing the routes from one routing protocol to another, use the command distribute-list in OSPF Router Configuration Mode. The no form of the command disables inbound filtering for the routes.
What is distribute list?
A distribute-list is used to control routing updates either coming TO your router or leaving FROM your router. Distribute-lists work on a variety of different IOS routing protocols. Because of that, learning how to use distribute-lists is very valuable.
How do you prioritize OSPF routes?
Where can OSPF routes be filtered?
There are two points at which OSPF routes can be filtered: within an area, or between areas on an area border router (ABR). This article discusses the differences between the two and the considerations which should be made when implementing OSPF filtering. The following topology is provided for illustration of both cases:
How do I eliminate all OSPF ads within a given area?
Using this method, filtering routes into area 0 eliminates their advertisement within all OSPF areas in the routing domain except the originating area. Filtering routes into a non-backbone area eliminates their advertisement only within the target area.
How does OSPF use link-state logic?
OSPF use pure link-state logic for intra-area routes, with full topology information about an area, piecing together the topology map from the Type 1 and Type 2 LSAs. This logic relies on all routers inside the area having an identical copy of the link-state database (LSDB) for that area.
How do I implement inter-area filtering (filtering between areas)?
We can implement inter-area filtering (filtering between areas) on R3 to prevent the route from being advertised outside of area 10. First, we define a prefix list on R3 to deny the 192.0.2.0/24 prefix and allow all others:
