ospf timings

Answered Question
Oct 13th, 2007

Hi,

I've got the following setup:

2 routers, each in a building.

the 2 routers are connceted to each other via a laser and wifi for backup.

with ospf I've got the configuration that wifi takes over when the laser goes down, or when the weather goes bad (rain, fog).

But as you know, weather is unpredictable. So if the laser link goes down, and gets back, I don't want the laser link get active right away (due to fog), but just after 15 minutes or so.

I've tried to change the ospf timers, but the delay of adding the ospf database to the routing table also affected my wifi redundancy timings.

So I tried 2 separate ospf processes, but that didn't work out as I would like it to be.

Anyone with a thought about this?

Correct Answer by Edison Ortiz about 9 years 4 months ago

You can build a GRE tunnel between the locations and use the ethernet interface layer3 information as the source and destination for the tunnel.

Make sure to enable keepalives in the tunnel in order to detect the link failure.

Once you do that, apply a backup delay on the tunnel interface pointing to the wifi interface.

The wifi interface will remain down as long as the tunnel is up. Once the tunnel goes down, the wifi interface will go up and when the connectivity returns in the tunnel, you can see the delay to the time you desire.

Both interfaces will be up at that time so make sure the wifi interface has a better OSPF cost.

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Richard Burts Sat, 10/13/2007 - 09:36

Gaston

I am not clear whether it would work for your requirements but these is an interesting feature which has been introduced into IOS for IP Event Dampening. The basic premises of this is that if an interface is flapping the routing protocols (including OSPF) will not use the interface until it has become stable. If you are interested this link has good information about the feature:

http://www.cisco.com/en/US/products/ps6350/products_configuration_guide_chapter09186a0080457c1d.html

HTH

Rick

gaston.bougie@v... Sat, 10/13/2007 - 14:09

Thank you all for the fast reply's.

unfortunatly when the laser link goes down, the laser doesn't tear down the ethernet interface that's connected to the router interface.

The laser is a stupid converter device.

I can't solve this on layer 2.

Therefore I'm wondering how I can get this "delay" implemented within routing.

i hoped that eigrp or ospf has a function for this, otherwise I'm thinking of bgp.

Thank you again for posting this fast.

Correct Answer
Edison Ortiz Sat, 10/13/2007 - 16:49

You can build a GRE tunnel between the locations and use the ethernet interface layer3 information as the source and destination for the tunnel.

Make sure to enable keepalives in the tunnel in order to detect the link failure.

Once you do that, apply a backup delay on the tunnel interface pointing to the wifi interface.

The wifi interface will remain down as long as the tunnel is up. Once the tunnel goes down, the wifi interface will go up and when the connectivity returns in the tunnel, you can see the delay to the time you desire.

Both interfaces will be up at that time so make sure the wifi interface has a better OSPF cost.

gaston.bougie@v... Tue, 10/16/2007 - 12:39

Thank you EdisonOrtiz,

this is exactly the sollution for my layer 2 problem: Create a tunnel and use this interface which checks the underlaying 3 connection instead of the layer 2 that doesn't go down.

Regards,

G

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