[Babel-users] battling with babel and route changes

[Dave Taht]

On Wed, Jun 22, 2011 at 12:27 PM, Julien Cristau <jcristau at debian.org> wrote:
> On Wed, Jun 22, 2011 at 08:35:53 -0600, Dave Taht wrote:
>
>> In order to disrupt a flow less, babel could
>>
>> A) install a new route with a higher metric (priority)
>> B) remove the old route
>> C) install the new route again with the right metric (priority)
>> D) Remove the new route with the higher metric
>>
>> instead, right now, when metrics are equal (which they usually are) it
>> removes the route entirely, leaving a window where packets drop
>> (particularly under load), then adds it again going to the right place.
>>
>> It SHOULD be easier than this, and perhaps babeld is working around an
>> old bug in the kernel here, but I don't think so. The above is kind of
>> crufty, and I hope it's just possible to combine C and D into one
>> operation.
>>
> 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.

Awesome. When I had tried this last, about 2 years ago, I ended up
with routes to nowhere getting stuck permanently sending things to
localhost. Perhaps this was another bug entirely (or my bug) and/or
has been fixed since then.

It was very hard to trigger, but when triggered, babel got wedged and
stayed wedged.
(it was very hard to debug,too, as when a node got wedged, it rapidly
went completely offline)

I will try eliminating the current work-around logic, or trying
something more robust, and see what happens on 3.0 and 2.6.37.6, which
are what I'm using at the moment.


>
> Cheers,
> Julien
>



-- 
Dave Täht
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