OSPF VRF-lite process limitation

[jaroslav.stolicny]

Hello All,

I would like to ask if there is any VRF limitation when talking about OSPF VRF-lite processes on the Cisco ISR 3945. 

Let`s say I would need to have 50-60 OSPF processes, separate ones for each VRF where in each VRF would be present around 10k routes. Is it something what might fry the router completely?

Thank you very much for your answer.

Jaro

[Peter Paluch · Accepted solution]

Hi Jaro,

There is a certain limit of routing information sources within each VRF (including the global routing table). Every routing information source consumes a data structure in IOS called the Protocol Descriptor Block (PDB). On a 7200 IOS I've tested in Dynamips, the limit was 30 PDBs per VRF. Connected routes consume 1 PDB in total, and static routes (if you have any configured) consume another 1 PDB in total, so in the end, you can have 28 - 29 instances of dynamic routing protocols at most. Each OSPF instance consumes one additional PDB. Remember, these limits are per-VRF; each VRF has its own set of 30 PDBs.

So this means that as long as you are going to run a single OSPF per VRF, you're safe, the platform will allow you to configure it.

However, I am not certain about your network design. To have a single router carry 50x to 60x 10K routes and have 50-60 OSPF processes with at least one adjacency in each VRF looks like too much work for a single router. What are your design options? Why do you need a single 3945 to carry such an extensive burden?

Also, is there any possibility of collapsing the number of routes in the individual VRFs? 10K routes looks like a lost opportunity for route summarization.

Any additional information about your network would be most welcome.

Best regards,
Peter

[jaroslav.stolicny]

Hi Peter, 

Thank you for your reply and thorough explanation. I was/am not in the position to influence a design decisions on this project. I just need to somehow think of possible solutions in the most elegant/reasonable way.  I agree we should be receiving routes from other network devices summarized. I will suggest that to the team responsible for the devices we are receiving routes from.

Thank you once again. 

Jaro

[Peter Paluch]

Hi Jaro,

You're very much welcome.

I was/am not in the position to influence a design decisions on this project. I just need to somehow think of possible solutions in the most elegant/reasonable way.

Okay, but what is the problem you're trying to solve? :) You see, you've asked about a possible solution (having a router with 60 VRFs, one OSPF process per VRF and 10K routes in each VRF) - but what is the problem that this solution should apply to? Perhaps if we know your situation better, we can suggest another ways of accomplishing your needs.

Best regards,
Peter

[Mark Malone]

Hey

I think there is a limit in general to the amount of processes you can have running on a router about 32 unless its been increased

7600s can only handle 28 so I couldn't see you getting 40-50 on a 3945 anyway

. Cisco IOS has a limit of 32 routing processes. Two of these are saved for static and directly connected routes. The Cisco 7600 router supports 28 OSPF processes per VRF.

[jaroslav.stolicny]

Hi Mark,

Thanks for your response. It has been most probably increased as friend of mine tried to simulate it on real 3945 and he was able to run 40-45 VRFs and for each one OSPF process without any issue. 

Jaro

[mehdidahane]

Hi,

I have a similar requirement but was wondering if there is a way to have multiple VRF under a single OSPF process in IOS on Cat6k?

Cheers
Mehdi