On Mon, Sep 15, 2003 at 11:50:24AM +0200, Michael van Elst wrote:
> I have analyzed the problem.
> 
> What happens is that gif caches a route to the tunnel destination
> when a packet is sent in netinet/in_gif.c:in_gif_output() line 200ff.
> 
> When the underlying interface (tun0) is down, then gif will cache a less
> specific route, in my case this is the default route.
> 
> When the underlying interface comes up, a more specific route
> is created but not used by gif. The cached route is dropped only
> when the gif interface is recreated (as described in the PR) or
> the tunnel destination address is changed.
> 
> I don't know any method to make gif aware of an added more specific
> route. So there are three possible solutions:
> 
> - ignore the problem. The kernel is dumb and some userland process
>   must trigger the cache flush.
> - drop the caching code, packets sent through gif must be routed
>   twice and tunnel performance will be reduced.
> - add a TTL to the cached route so that sooner or later a correct
>   route will be picked up, the performance penalty will be small.
> 
> Suggestions ?

A TTL for the cached route is probably the way to go.

-- 
Manuel Bouyer <bouyer@antioche.eu.org>
     NetBSD: 24 ans d'experience feront toujours la difference
--