OSPF route summarization

[david-schroeder_2]

I have attempted to summarize my OSPF routes using the "area x range x.x.x.x x.x.x.x" statement as described in the Cisco documentation for route summarization. I run 12.0(7) on the ABR router so I used a default route statement also(as recommended by Cisco). I have tried on several occasions to get the summarization to work but have encountered routing problems to the areas that I attempt to summarize.

Does anyone have examples of the OSPF statements and any default route statements that are needed to successfully do this?

Thanks,

Dave

[david-schroeder_2]

I additionally have 10.60.129.18/30 10.60.129.10/30 and 10.60.129.22/30.

I also have 10.60.147.1/24, 10.60.148.1/24 and 10.60.149.1/24. I have chosen our smallest area to test with first to ensure I can get summarization working. I have other different areas to summarize that have hundreds of routes within them. I used the summary statement to try to encompass any subnet between 10.60.128.0 and 10.60.254.0. Maybe I am incorrect in doing it that way.

Thanks a bunch,

Dave

[thisisshanky]

By summarizing such a huge range, you would be creating problems, later on while summarizing at other ABRs. Its always better to summarise to the next highest (supernet) prefix that is available).

I would recommend using two summarization commands, to summarize the 10.60.129.x and 10.60.147.x networks separately.

The networks falling in the 10.60.129.x range are,

10.60.129.12/30

10.60.129.16/30

10.60.129.20/30

In this case your best bet summary would be 10.60.129.0/27

The networks falling in the 10.60.147.x range are,

10.60.147.0/24

10.60.148.0/24

10.60.149.0/24

The best summary would be, 10.60.147.144/21

Your commands should apper as,

area 5 range 10.60.129.0 255.255.255.224

area 5 range 10.60.147.144 255.255.248

Hope its now clear.

[david-schroeder_2]

I will try what you have suggested. Thanks for your prompt and informative answers.

Dave

[jmcoffey]

The area range command will only summarize OSPF routes at the ABR. You will still see the external networks. If you have external routes in this area they must be summarized at the ASBR not the ABR.

Sorry if I am way off in left field on this reply and this is a purely OSPF area.

Jim Coffey

[david-schroeder_2]

Jim,

Thanks for your input. I am trying to summarize OSPF areas only at the ABR. I'm trying to reduce the size of my routing table in all my enpoint routers. So far, I have had no success in getting the summarization to work as advertised.

I have a subnet outside of my ospf areas that I have trouble getting to when I do the summarization. I use the IP classless statement but I don't have a default route coded for this subnet. I am thinking that I need to have a default route coded for any subnet that does not fall within my summarization range and that is what I'm going to try.

Thanks for responding and let me know if I'm way of base with my idea.

Dave

[thisisshanky]

Hello David,

I hope you were able to solve the previous problem you had with summarization. If not let us know, the exact problem you are facing again.

For the network, that is outside the area, instead of setting a default route, it would be much better to redistribute that route. If you include a default route instead, to reach this network, that would become a more general route, and in future, if you plan to use defaults in OSPF, this can cause problems.