Re: [LARTC] problem in routing

["Martin A. Brown" <mabrown-lartc@securepipe.com>]

 : Ok..
 : i've done that without success.
 : Please watch that the routing is made in the router machine and the
 : marking is made in the linux box before and because of that it doesn't
 : matter where i mark the packets.

Ah, now I understand!  But it does matter, tremendously.

I didn't perceive in your previous post that you had two hosts.  Perhaps I 
was being dense.

The "fwmark" is a field on the packet which only exists in the data 
structure used to represent the packet on a single machine.  In short, the 
fwmark does not survive a single machine.  As soon as the packet is 
transmitted, the fwmark is lost.

You could use the mangle table with the TOS target and then change your ip
rule to route based on ToS.  I'm unsure of the implications for your
network, but this is a possible solution.  If you modify the ToS on the 
packet, this will be visible to other hosts.

Good luck,

-Martin

 : Thanks anyway
 : Nuno Fernandes
 : 
 : On Tue, 2002-11-12 at 15:51, Martin A. Brown wrote:
 : > Hello Nuno,
 : > 
 : > I'd suggest s/POSTROUTING/PREROUTING/ here:
 : > 
 : >  : iptables -t mangle -A POSTROUTING -d SOME.IP.IN.INTERNET -j MARK
 : >  : --set-mark 21
 : >  : 
 : >  : In my ROUTER i want to redirect packets according to MARK and i'm doing:
 : >  : 
 : >  : root@euroter(~)# more /etc/iproute2/rt_tables 
 : >  : 255	local
 : >  : 254	main
 : >  : 253	default
 : >  : 200	over
 : > 
 : > Consult Stef Coene's kernel packet traveling diagram, which should 
 : > explain (visually) why you want to mark the packet before the routing 
 : > stage.
 : > 
 : >   http://www.docum.org/stef.coene/qos/kptd/
 : > 
 : >  : root@euroter(~)# ip route ls table over
 : >  : default via XXX.XXX.XXX.XXX dev eth1
 : >  : 
 : >  : where XXX.XXX.XXX.XXX is the gateway of the provider 1.
 : >  :
 : >  : Doing ip rule ls, i can see that all packets with mark 21 go to table
 : >  : over.
 : >  : root@euroter(~)# ip rule ls 
 : >  : 0:	from all lookup local 
 : >  : 32765:	from all fwmark       21 lookup over 
 : >  : 32766:	from all lookup main 
 : >  : 32767:	from all lookup default 
 : > 
 : > Naturally, the RPDB (displayed with "ip rule show") is consulted as part 
 : > of the routing process.
 : > 
 : > So, in short, your host euroter is doing as follows:
 : > 
 : >   - routing the packet
 : >   - marking the packet
 : >   - transmitting via provider2
 : > 
 : >  : And table over only has default gw, but when i do a
 : >  : ping XXX.XXX.XXX.XXX it goes throw proveider2 and not provider1.
 : > 
 : > Good luck,
 : > 
 : > -Martin
 : 

-- 
Martin A. Brown --- SecurePipe, Inc. --- mabrown@securepipe.com



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