Re: Problems in Dead Gateway Detection / Failover - Multiple ISP Links

Linux Advanced Routing and Traffic Control

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Eduardo Fernández wrote:
Hi!

Did you finally write a script for dead gateway detection beyond first
hop? Did you find any other solution to this problem? I'm quite
interested and I bet other multipath users here are interested too.

My linux router has 10 dsl links (adding 15 more in short), when one
of the dsl routers goes down the kernel does not always notice. Don't
know why. Also, if a dsl route is up but the internet link is down
dead gateway detection doesn't work either.

Thanks!

Edu


If you follow the nano.txt procedure and apply the patches, it works perfectly as long as the first hop is dead. But to ensure failover, when connectivity goes down at any of the hops, you can use the nano.txt for configuring the interfaces and multipath routes (call it default configuration) and also run a script in the background to modify the routes as described below.

1. Periodically keep on checking if a remote host is reachable from each of the gateways by pinging it after every n seconds.

2. If the remote host is not reachable after a number of tries (which you can decide according to your own specific situation) from a particular gateway, remove that route. If you have just two internet links, there would be only one gateway left. But if you have more than two links alive you can again define multipath routes with appropriate weights for the active gateways. The possible combinations will increase exponentially with the increase in number of internet links so you will have to factor is all the cases in the script.

3. Restore the default configuration when the remote host is reachable from all the gateways.

I am not too sure how its going to behave with 10 links because if the links are not so stable it will result in very frequent changes.

--
Manish Kathuria
http://www.tuxspace.com /

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