Cisco Support Community
cancel
Showing results for 
Search instead for 
Did you mean: 
Announcements
Webcast-Catalyst9k
New Member

RIP/OSPF Filtering 30bit nets from 22 >= bit nets

Here's the deal: We have a "TCP enhancer" device hanging off of a 7200 router that is learning routes through OSPF from the same 7200 and announcing them back into the 7200 as RIP routes--this is how the device grabs traffic. I need to block certain /30 networks that I do not want the device to announce. Problem is, we do not have control of this device so I have to regulate it from the 7200. For example, I want to prevent the device from announcing 10.10.10.10/30 but since this device is announcing 10.10.10.0/24, a distribute-list or prefix-list will not block it. There are way too many /30s to add static routes for and changing the RIP preference will negate the device. Any suggestions? Thank you in advance!

4 REPLIES
Hall of Fame Super Gold

Re: RIP/OSPF Filtering 30bit nets from 22 >= bit nets

Maybe there is something in this environment that I am not understanding correctly. If the device is learning routes via OSPF and redistributing via RIP, then what it advertises via RIP should have an administrative distance greater then the original OSPF distance. And if there are /30 routes that are being summarized into /24 by RIP then the 7200 should prefer the more specific route to the summarized route. Perhaps you can help us understand this a bit better?

HTH

Rick

New Member

Re: RIP/OSPF Filtering 30bit nets from 22 >= bit nets

Rick: You're right. Correction to my previous post: The 7200 announces the larger subnets and the TCP device grabs smaller chunks of that. So lets change the previous example to the 7200 announces 10.10.10.0/22 and the TCP device announces 10.10.10.0/23 back to the 7200--the /23 is preferred. The /30 routes that I need to block are not being announced by the device so I can't specifically block them. To add more confusion to the matter, here is another example of what I need to block in wildcards:

0.0.0.48 255.255.255.3

0.0.0.52 255.255.255.3

0.0.0.56 255.255.255.3

0.0.0.152 255.255.255.3

.../30s that are .48, .52, .56, and .152 nets of any /24. :-)

Hall of Fame Super Gold

Re: RIP/OSPF Filtering 30bit nets from 22 >= bit nets

Carl

There still are some things I am not clear about in your situation, especially what the device is really advertising and what subnets you are really interested in. If the device is advertising aggregated blocks (10.10.10.0/23) and you are interested in /30s then there is no distribute list that will solve your problem.

I wonder if a policy routing solution might work (especially based on your example with wildcards it seems like it might). If it is true that any .48/30, any .52/30, and .56/30, or any .152/30 should be routed differently then I think that Policy Based Routing might solve your problem. In the Policy Based Routing Route Map you can build an access list that will identify these subnets and can specify what next hop to use for them.

HTH

Rick

New Member

Re: RIP/OSPF Filtering 30bit nets from 22 >= bit nets

I considered the same but the problem is, there are 20 next hops for 80 /30s. It's a tricky issue. Thank you for your input thus far Rick. Any other suggestions?

149
Views
0
Helpful
4
Replies
CreatePlease to create content