[LARTC] Re: Problem with iptables with -j TOS and MARK

[Jarek Poplawski <jarkap@poczta.onet.pl>]

On 28-07-2006 15:57, Jarek Poplawski wrote:
> On 28-07-2006 14:43, makevuy wrote:
>> Hy,
>>
>> I would want to mark the packets that are entering in a machine, with 
>> a mark for using diffserv with DSMARK.
>>
>> My machine has 2 interfaces, a ethernet and a wireless. The ethernet 
>> interface is eth1 and the other is wifi0.
>>
>> Firs, I would want to test that I would be able to mark the tos of the 
>> paquets that I would be receiving, for this I write in the console of 
>> my linux:
>>
>>
>> iptables -A PREROUTING -i eth1 -t mangle -p udp -j TOS --set-tos 0x20
>>
>> But the TOS doesn't change (I see this with ethereal)
>>
>> Waht could be the problem?
> 
> If I can remember, TOS is inserted for real some time later, so try to 
> investigate on forward or postrouting.

After short weekend testing my memory turned out to be faulty 
again - it can remember only every second bit (because it's old!).

Iptables -j TOS and -j DSCP should change a tos field of ip 
headers at once (this could be seen with -j LOG everywhere after 
this setting). This field can influent the way a packet is 
classified by some qdisc like prio, but not directly - inner 
priority field is taken for this. And this priority is computed 
from tos only in forward.

So probably ethereal showed packets before changes or you have 
some problem with iptables.

Jarek P.

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