Re: [LARTC] problem in routing

[Nuno Miguel Pais Fernandes <npf@eurotux.com>]

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Dam :)

The reason why i mark the packets in the linux box is because the router
is a minimlistic kernel.. without mangle support :(

I'll try it and then put the notes in the mailling list if i succeed :)

Thanks anyway.

On Tue, 2002-11-12 at 16:19, Martin A. Brown wrote:
>  : 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
>  : 
-- 
Nuno Miguel Pais Fernandes <npf@eurotux.com>
Eurotux S.A.

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