3

I am busy redesigning my OSPF network to break it up into different areas and use route summarization to reduce the size of my LSDB and then setup MPLS. It is a rather large network with a thousand+ routers on the backbone area(Hence the need to redesign this).

I have come across an issue which I am trying to figure out a way around. An example area which I am creating has 2 connections to the backbone, so 2 ABRs. I configure summary routes in each of the ABRs, and everything seems to work nicely.

The problem comes in when some link between 2 routers in the middle of the area goes down. Now, the summarized routes get distributed from both ABRs as normal, and only the lowest cost route gets used by the backbone. So the backbone only ends up with the one path to the summarized route towards one of the ABRs. This leaves the other side of the area isolated from the network, because the backbone routes all requests to the entire supernet, to the one ABR, and some of the routers are on the other side of the link that is down, from the ABR where the backbone is routing the supernetenter image description here to

Is there a best practice way to get around this? How do people handle this situation?

Please let me know if my description is not clear enough.

  • 1
    Don't summarize your routes. – Ron Trunk Apr 15 '17 at 13:29
  • 1
    Split the /20 into two networks – user3476261 Apr 16 '17 at 8:42
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer. – Ron Maupin Feb 19 '18 at 4:09
2

Implement IBGP with a lower preference than OSPF and import summary routes narrow with a route-filter policy and define additional BGP attributes with the algorithm based on your need.

RPM with static routes. Not all routers have this, maybe a firewall or other device.

Event policy with a script. If possible and depending on: platform, urgency, and knowledge may not be the most suitable.

As user3476261 said, split the network, administratively not always possible.

As Ron Trunk suggested do not summarize, although based on your need you are looking to reduce control plane burden, hence not likely.

Get more cabling done for redundancy (not scalable).

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.