[Babel-users] battling with babel and route changes

[Dave Taht]

On Wed, Jun 22, 2011 at 3:57 PM, Juliusz Chroboczek <jch at pps.jussieu.fr> wrote:
>> I believe this is indeed working around an old kernel bug.  We needed to
>> make this work with some old 2.4.x kernel.  A quick test on 2.6.32
>> suggests that adding a two routes with the same metric and different
>> gateways works just fine now.
>
> I may be wrong, but I believe that this is due to IP_ROUTE_MULTIPATH
> being enabled in your kernel, and has nothing to do with the kernel's
> vintage.

Interesting. I did go to the trouble of coding up a solution that
tried to add then delete, and fell back to the old behavior if it had
trouble... and I just survived a thunderstorm with it. Thus far, no
kittens eaten...

> Dave, please note that the window when there's no route is very short --
> it lasts just a few microseconds --, so you'll typically lose just
> between 0 and 1 packets on a route change.

It seemed considerably higher than that on a busy router. My
assumption was that
the process could be rescheduled between the calls to netlink, while
considerably more work was getting done in a softirq...

Or (as usuall) I'm battling another bug. I'm getting closer to where I
can finally get insight into the behavior of huge streams on tiny
routers by the day...

That said, since I just coded up the solution I'll try to time the
transaction somehow
to gain some better insight (without skewing the test)...
> I agree that it should be
> fixed, and using Linux' ability to do multipath is a good workaround, as
> long as it doesn't break babeld on non-multipath kernels.

I do like the idea of using multipath to a greater extent.

>
> -- Juliusz
>



-- 
Dave Täht
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