LARTC - Sep 2002 - Requset regarding packet marking.

Hello Sir,

I want some help from you. I have my configuration like this. I 
have three machines. PC1,PC2,PC3.

            hub                        hub
PC1--------------------PC2-----------------------PC3
eth0                eth0,eth1                    eth0



I want to work my configuration like diffserv. I am generating 
traffic from PC3 and sending it to PC1 via PC2(as a router)and 
 from PC2 to PC1 also. So i have two kinds of traffic. I want to 
do these things:

1. Mark the packets going out from PC3 towards PC1 via PC2.

2. I have my rules and filters with tc in PC2. Means i want to 
contol the traffic from PC2. Based on the mark which i put on the 
traffic going out     from   PC3 i want to put the traffic in 
different-differnt classes. Means i want to filter the traffic 
based on the mark on traffic. It would be helpful if i am  able to 
mark the TOS bits so that i can see it in tcdump or ethereal.

3. Traffic going out from PC2 and generated by PC2 itself should 
have different differnt mark so that the traffic can be filtered 
based on the mark.

Please suggest sthing related to this.

Waiting for your reply.

Anish Mehta.
ENST-Bretagne.



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On Thursday, 05 September 2002, at 16:57:53 -0000,
anish_46628 wrote:
> 3. Traffic going out from PC2 and generated by PC2 itself should 
> have different differnt mark so that the traffic can be filtered 
> based on the mark.
> 
With linux kernel 2.4.x, packets go through different sets of rules when
"traversing" the box. A packet in transit will enter PREROUTING, pass
on
to FORWARD and finally to POSTROUTING just before being queued to be
sent out on the physical interface. On the other hand, locally generated
packets go first to OUTPUT and afterwards to POSTROUTING. Compare this 
to kernels 2.2.x when an in-transit packet would be seen at input, forward 
and output.

There is an _excelent_ reference on iptables you should check to get the
details of what you can do and how:
http://people.unix-fu.org/andreasson/iptables-tutorial/iptables-tutorial.html

-- 
Jose Luis Domingo Lopez
Linux Registered User #189436     Debian Linux Woody (Linux 2.4.19-pre6aa1)
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Sorry to nitpick, but the tutorial actually moved some time ago. There was 
simply too much troubles with hosting, so I finally got a domain of my own 
(frozentux.net), and the tutorial is available at 
http://iptables-tutorial.frozentux.net, hosted by haringstad.com which 
looks really really good so far. Of course, if they would go down, i will 
always be able to move the DNS to somewhere else in the future instead...

Anyways, just to let everyone know. I got some other things under 
development as well right now, hence the iptables stuff is pretty much at 
a "featurefreeze".

Have a nice day!

----
Oskar Andreasson
http://iptables-tutorial.haringstad.com
http://people.unix-fu.org/andreasson/
mailto:blueflux@koffein.net


On Fri, 6 Sep 2002, Jose Luis Domingo Lopez wrote:
> On Thursday, 05 September 2002, at 16:57:53 -0000,
> anish_46628 wrote:
> 
> > 3. Traffic going out from PC2 and generated by PC2 itself should 
> > have different differnt mark so that the traffic can be filtered 
> > based on the mark.
> > 
> With linux kernel 2.4.x, packets go through different sets of rules when
> "traversing" the box. A packet in transit will enter PREROUTING,
pass on
> to FORWARD and finally to POSTROUTING just before being queued to be
> sent out on the physical interface. On the other hand, locally generated
> packets go first to OUTPUT and afterwards to POSTROUTING. Compare this 
> to kernels 2.2.x when an in-transit packet would be seen at input, forward 
> and output.
> 
> There is an _excelent_ reference on iptables you should check to get the
> details of what you can do and how:
>
http://people.unix-fu.org/andreasson/iptables-tutorial/iptables-tutorial.html
> 
> 

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