RE: [LARTC] Re: Routing that doesn't route

[Julian Anastasov <ja@ssi.bg>]

	Hello,

On Wed, 1 May 2002, Greg Scott wrote:

> is all about.  I'm still not clear about RP_FILTER but
> getting better.

	Simple thing: IP or ARP packet is accepted only if
there is a route in reverse direction, i.e. when the addresses
are reversed. Example:

packet 10.0.0.1->10.0.0.2 is coming from eth0 and we have a
route to 10.0.0.1 via eth0, so the packet is accepted from the
reverse path protection (rp_filter) set on eth0. If this
packet comes from eth1 (again with rp_filter=1) then it will
be dropped because we already have a route via eth0. As
result, packets from 10.0.0.0/24, for example, should come
only from eth0. In any other case, they will be dropped from
other devices with rp_filter protection and always allowed
from devices without such protection.

	The rp_filter is also explained here:

http://lartc.org/HOWTO//cvs/2.4routing/html/c1182.html#AEN1188

> reproduced the problem at my place.  Then I setup a system
> with Red Hat 7.2, which uses kernel 2.4-7.  Still old, but not
> as old!  I set this sytem up as a router in parallel with my
> other Linux router and ran the same tests again.  This time,
> everything did what it was supposed to do.
>
> So I think the whole thing was a bug with the 2.4-2 kernel.

	Yes, testing with latest kernel should be the first
thing to try :)

> thanks
>
> - Greg

Regards

--
Julian Anastasov <ja@ssi.bg>

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