OSPF intra-area route summarization 1

[rpast]

Hello all,

I have an OSPF question. How do you summarize intra-area routes? I know all about ABRs between areas(using ‘area range’) and ASBRs between ASs (using ‘summary-address’). But just within one area 0, how do I summarize addresses upwards from the distribution to the Core? With EIGRP or RIP, it’s easy (‘ip summary-address’), but this command is not available for OSPF -- and 'summary-address' is meant only for ASBRs.

Thanks,

 

[unclerico]

Unfortunately, as you know, the only routers that can summarize anything are ABR/ASBRs for Inter-Area routes. Intra-area routes do not get summarized. EIGRP and RIP do not have anything similar to OSPF in terms of areas or a distribution/core setup. The closest thing you'll find is in EIGRP with the stub router that has only a single entry point to the larger network.

But just within one area 0, how do I summarize addresses upwards from the distribution to the Core

If you just employ a single area then there is no distribution/core. Area 0 is the "core" so some clarification is needed. I apologize if I'm missing something or if I'm stating what you already know.

I hate all Uppercase... I don't want my groups to seem angry at me all the time! =)
- ColdFlame (vbscript forum)

 

[rpast]

Thank you for your response. Yes, the terms 'distribution' and 'core' are relative. In smaller networks, using EIGRP, I have created a core/distribution/access topology, where there was certainly a use for chopping up a class B into smaller subnets, and then summarizing them up to the 'core.' Now, I'm working with non-Cisco routers,forced to use OSPF, and don't have nearly the number of routers to warrant splitting the network up into separate areas. But I'd still like summarize.

Maybe the only answer is to split the network into separate areas, even though the number of nodes is not large. Is it customary to do this? Or is more common just to forego the orderly VLSM usage that is touted as best practice?

Thank you, again.

 

[burtsbees]

Why not just use the bigger mask in the network statements, as well as routes and acl's? For example, in a Cisco...say you have 6 vlsm subnets within a class C, like 192.168.1.0/24, and the subnets are all /29, like 192.168.1.0, 1.8, 1.16, 1.24, 1.32 and 1.40. You can summarize with a /26 like so...
router ospf 65
network 192.168.1.0 0.0.0.63 area 0

This covers all the vlsm's...

Burt

 

[unclerico]

Now, I'm working with non-Cisco routers,forced to use OSPF, and don't have nearly the number of routers to warrant splitting the network up into separate areas

That was going to be my next question. How big are your routing tables? Are you going to run into resource problems such as memory for the routing table or processor utilization when SPF is run? This will be the deciding factor for you to implement multiple areas.

Maybe the only answer is to split the network into separate areas, even though the number of nodes is not large. Is it customary to do this?  Or is more common just to forego the orderly VLSM usage that is touted as best practice?

I hear what you're saying here. As long as your routers are sized to accomodate a single area toplogy then I would just leave it at that. Just be sure to designate your DR/BDR (if applicable in your toplogy) on your beefiest routers. You are trying to be a good admin here and want to be as efficient as possible which is commendable, but if it was me I would just leave it in one area. Of course maintain your hierarchical addressing in case things change down the road and you want to implement multiple areas so that you can use the area range (and summary-address if needed) to summarize into other areas.

bert, that won't work like you think it will. All that is doing is telling the ospf process to start advertising on all links that are in the range of 192.168.1.0/26, it doesn't actually summarize them. I really wish it did though.


I hate all Uppercase... I don't want my groups to seem angry at me all the time! =)
- ColdFlame (vbscript forum)

 

[burtsbees]

You are correct, but it was too late---I hit the submit post button already...lol
The other choice would be RIPv2, so long as there are less that 50 routers total, and no router has to beyond 15 hops...

Burt

 

[rpast]

Thanks very much guys. Yes, OSPF does not auto-summarize. I like your solution, uncle -- and the replies from you both, confirming what I suspected. Bigger (i.e. higher-tech) isn't always better. There's definitely a place for EIGRP and RIP in smaller networks.