Re: [LARTC] Problems in Dead Gateway Detection / Failover - Multiple

[Manish Kathuria <manish@tuxspace.com>]

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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