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

[thisisshanky]

David, Do you have a discontigous network addressing scheme in your network....That can create routing problems, during summarization. Also since your version of IOS is below 12.1(6) you need to manually configure the summary route pointing to null0 interface on the local router which is summarizing.

Visit this for more details http://www.cisco.com/warp/public/104/3.html#12.0

Perhaps if we could get a picture of your network + some configs (relevant) we might be able to troubleshoot more...

Hope that helps!

[david-schroeder_2]

The areas I am summarize have contiguous addressing. I have included an example of the config below:

ip route 10.60.128.0 255.255.128.0 null0

router ospf 1

area 5 range 10.60.128.0 255.255.128.0

I removed the following statement from router ospf 1:

network 10.60.128.0 0.0.127.255 area 5

The ABR router that I'm working with is the core router(area 0).

When I implement these changes, my routes to the area 5 subnets use the default route for area 5 subnets and then I cannot get to those subnets.

Thanks for your quick response.

Dave

[thisisshanky]

I see that, before summarization you had the command,

network 10.60.128.0 0.0.127.255 area 5 - which means, this router has an interface configured with an ip address from network 10.60.128.0/17 and that interface is in area 5. and OSPF is enabled on that interface.

Now you have given a summarization command "area 5 range 10.60.128.0 255.255.128.0 ".

The removal of the network command, actually disables OSPF on the routers interface with ip address from 10.60.128.0/17. So that is the reason why, you were not able to reach routes in area 5.

After the removal of the command, give a "show ip ospf neighbor" on this router, and see if there are any neighbors in area 5 through the corresponding interface.

Solution is that, you should not remove the network command, because, that is the key command, which enables OSPF on an interface.

Hope that helps!

[david-schroeder_2]

Thanks for the info. So the key being that the network statement must remain and you then add the area 5 range statement to perform the summarization.

I'll give this a try.

I should be able to see only one route advertised for area 5 within an another areas router(area 1 for example) when everything is all said and done?

[thisisshanky]

Yes thats correct.

[david-schroeder_2]

I added only the area 5 range statement and the default route statement for that range and I can get to my area 5 routers.

How can I tell if the summarization is actually taking place? I've looked on other areas routers and still see the routes for each subnet in area 5. I though I would only see the area summarization route or statement. Maybe I'm not looking in the right place to see if my routing table is actually smaller.

Thanks,

Dave

[mark-obrien]

Dave,

Do you have more than one ABR in area 5? You need this same summarization on all ABRs.

Mark

[david-schroeder_2]

Mark,

I only have one ABR for area 5. I have other routers in area 5 but they are only in area 5. I have not changed anything in my area 5(only) routers at this point.

I'm assuming you mean the ABR is the router that touches area 5 and area 0 which is the case here.

Thanks,

Dave

[thisisshanky]

Perhaps, there could be a mistake in the summarized prefix, wrt the individual prefixes. Please paste your summarized prefix, along with individual ones, so that we can check out if the summarization is correct.

[david-schroeder_2]

My summarization statement is as follows:

router ospf 1

area 5 range 10.60.128.0 255.255.128.0

my routing statement within ospf is as follows:

network 10.60.128.0 0.0.127.255 area 5

My default router for the summarized areas is:

ip route 10.60.128.0 255.255.128.0 Null0

When I do a show ip route | inlclude 10.60 on one of my area 1 routers I still get all my 10.60.129.x and above subnets in the list. I have made no changes to any of my area 5 routers as I did not think I would need to modify any OSPF statements on them.

Thanks,

Dave

[thisisshanky]

Hello Dave,

I understand clearly the above setup. But what I asked for in the previous posting, is this:

I want to know all the prefixes that your area 5 routers are advertising to this ABR.

I know that the summary is 10.60.128.0/17.

I need to know the individual prefixes and their masks that are involved in this summary, which your routers in area 5 are advertising. ( such as 10.60.129.x)

[david-schroeder_2]

Sorry about that. I have attached a partial config of one of the area 5 routers. It has the subnets and masks you asked for. Let me know what I'm overlooking.

interface Ethernet0/0

ip address 10.60.155.1 255.255.255.0

full-duplex

no cdp enable

!

interface Serial0/0

bandwidth 56

ip address 10.60.129.14 255.255.255.252

priority-group 1

router ospf 1

log-adjacency-changes

network 10.60.129.14 0.0.0.0 area 5

network 10.60.155.1 0.0.0.0 area 5

Let me know if I need to include additional info.

Thanks,

Dave

[mark-obrien]

Dave,

By any chance, do any of your routers have static routes to anything in the 10.60.128.0/17 range? If these routes are redistributed into OSPF, the summarization will not cover them.

Mark

[thisisshanky]

Yeah, got that,

I see that one of the links in area 5 is having a network address, 10.60.129.12/30. I wanted to know the reason why your summarization address is 10.60.128.0/17. For this i need to know the network address of all the links in area 5. The area 5 routes are still there in area 1 routes, because of wrong summarization. Please input the remaining /30 prefixes in area 5.