Re: [LARTC] Routing problem (RTNETLINK answers: Invalid argument)

["Brian J. Murrell" <brian@interlinx.bc.ca>]

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On Thu, 2007-02-15 at 00:30 +0100, Paul Viney wrote:
> Wow! That made a difference. One 
> echo "0" > /proc/sys/net/ipv4/conf/eth1/rp_filter
> and everything started working. 
> Thanks a lot Torsten and Alex - I wouldn't have solved it without your 
> suggestions.

But the question I have had about this subject is when one has two
default routes, load balanced, does this evaluation of which interface
would be used when the packet is reverse-path-tested test all of the
default routes or just the route that is currently active given the load
balancing algorithm?

If only the one, current default route is used in the evaluation it
seems to me even in the most straightforward
dual-load-balanced-default-route configuration there is a race between
the time a packet is assigned an outgoing address & sent out the then
current default route and the routing code re-balancing and switching
the active default route (i.e prior to the reply packet -- or even in
the middle of active tcp connections).

The situation gets even worse (not even just a race condition) when you
apply policy routing to force the use of a particular default route.

Thots?

b.

> 
> Paul Viney
> 
> 
> On Wednesday 14 February 2007 21:17, Torsten Luettgert wrote:
> > This is one of my favourites :-)
> >
> > Usually that problem is caused by the rp_filter feature, which silently
> > drops packets that arrive on an interface answers wouldn't be routed to.
> >
> > Just try
> >
> > for i in /proc/sys/net/ipv4/conf/eth*/rp_filter; do
> > 	echo 0 > $i
> > done
> >
> > and see if that helps.
> > (indeed, you don't really need to switch it off for all of them, just
> > the uplink interfaces would be enough)
> >
> > Hth,
> > Torsten
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> 
-- 
My other computer is your Microsoft Windows server.

Brian J. Murrell

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