[LARTC] DGD patch not detecting dead gateway

[Manish Kathuria]

On 1/19/07, Tom Lobato <tomlobato at gmail.com> wrote:
>   Hello all!
>
>   I applied http://www.ssi.bg/~ja/routes-2.6.8-10.diff patch to kernel
> 2.6.8.1 and it works fine, or almost fine. It does the load balancing
> well, but when one link is dropped it continues to try it.
>   At the end of http://www.ssi.bg/~ja/nano.txt it is said to ping
> gateway 1 and gateway 2, for the kernel to know if that route is
> working, but since my linux is connected to the links through 1
> dedicated link and one adsl modem, I tryied to:
>     1) remove ethernet cable from linux nic: the patch worked well,
> began to send traffic only to the yet working, link.
>     2) remove telephone line from adsl modem (or external ethernet
> cable from the dedic. link switch): the patch didn't work, continued
> trying to send traffic to the dropped link.
>   So, I think its happening because linux, since it can ping the
> switch (or adsl modem) thinks that link is good.
>
>   Did you have this problem? Some hint?
>   Thank you!
>

My experience has been mixed. The patch worked very well in many cases
but in some it worked only if the first hop gateway was down and not
any of the subsequent hops. So as you mentioned its happening since it
can ping the switch / modem, it thinks the link is good. You can make
a script which will keep on running in the background and check it the
links are up or not and if any of the links is down, it can change the
default route and provide a failover.

-- 
Manish Kathuria
Tux Technologies
http://www.tuxtechnologies.co.in/