Use table-map to filter OSPF routing issues

[haininghuang3185]

I want to filter OSPF intra-area routes (area0) on Nexus 7000s, but I found that the Nexus device does not support distribute-list, but uses table-map instead of distribute-list. Can I use the following command to filter the area in ospf? Within the 223.110.236.0/25(area0) address segment.

ip prefix-list ospf-guolv seq 10 permit 223.110.236.0/25
!
route-map ospf-guolv deny 10
match ip address prefix-list ospf-guolv
route-map ospf-guolv permit 20
!
router ospf 100
table-map ospf-guolv filter
!

[MHM Cisco World]

table-map 
A table map is a unique feature of NX-OS that allows the network administrator to filter routes or selectively modify the distance of the routes before the routes are sent to routing information base (RIB). 

so it same as distribute-list IN in ospf, it not add this prefix in RIB of this router but it not effect OSPF database

MHM

 

[haininghuang3185]

This means that I can use table-map to filter 223.110.236.0/25 routes in the area0? The configuration command is as follows:

ip prefix-list ospf-guolv seq 10 permit 223.110.236.0/25
!
route-map ospf-guolv deny 10
match ip address prefix-list ospf-guolv
route-map ospf-guolv permit 20
!
router ospf 100
table-map ospf-guolv filter
!

[MHM Cisco World · Accepted solution]

Yes 
it will deny 223.110.236.0/25 that learn from OSPF to inject to RIB and allow other prefix 
for more 
https://www.cisco.com/c/en/us/products/collateral/switches/nexus-7000-series-switches/white-paper-c11-733892.html

NOTE:- table-map ospf-guolv filter <<- no need filter keyword in end it can in feature effect BGP

The table map allows more scalable solutions by preserving valuable RIB memory. The table map can be used for both filtering routes and changing the route distance.

●   When the 

table-map

 command is used without the filter keyword, the route map referenced in the 

table‑map

 command is used to set certain properties (such as the traffic index) of the routes for installation in the RIB. The route is always downloaded, regardless of whether it is permitted or denied by the route map.

●   When the 

table-map

 command is used with the filter keyword, the route map referenced is also used to control whether or not a BGP route is to be downloaded to the RIB.

MHM

[David Ruess]

You can do that but make sure you understand the implications. I have not tested with a table map (just Distribute List) but if you use the table map I believe it will remove the route from the RIB but will NOT remove it from the database. This is a function of OSPF as the area needs the same OSPF database. That being said you would need to remove it and configure a table map for ALL devices in the area. Reason being, lets say you have 3 routers connected in a row like so: R1<->R2<->R3

If you configure a table map only on R2 then R2 wont install that route into its routing table (RIB), but it will send the LSA down to R3, which will install it into its RIB. This will show up in R3s routing table but it wont have reachability because it will send to R2 and R2 wont have a route in its routing table since its being blocked with the route map. Unless you have a default or other route to get to your network.

The filter keyword may not even be supported for OSPF (I know it is for BGP)

-David