IPTABLES: TOS setting problems

Hi folks,

I'm trying to get my linux router to set tos bits for Minimize Delay
(0x10) on packets for telnet. I've set this up but it doesn't work ! I
can see this using Ethereal.

According to the iptables counters, the packets are being matched OK -
the tos bits just aren't set. To rule out the possibility of other
aspects of my iptables mucking things up, I have tried a very basic
setup as follows:


#/etc/sysconfig/iptables

*mangle
:PREROUTING ACCEPT [0:0]
-A PREROUTING -p tcp --dport 23 -j TOS --set-tos 0x10
:OUTPUT ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
COMMIT

*filter
:OUTPUT ACCEPT [0:0]
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
COMMIT

I can see that packets for telnet are being matched OK using:

iptables -L -v -n -t mangle

but the differentiated services field is still 0x00 when I capture
packets in Ethereal !!

I don't understand, but I hope I am just missing something silly.
Please help me ;-)

TIA

Craig Jackson

craig.athome@virgin.net (craig) wrote in message news:<26ca3cec.0410050146.5e7466bb@posting.google. com>...
> Hi folks,
>
> I'm trying to get my linux router to set tos bits for Minimize Delay
> (0x10) on packets for telnet. I've set this up but it doesn't work ! I
> can see this using Ethereal.
>
> According to the iptables counters, the packets are being matched OK -
> the tos bits just aren't set. To rule out the possibility of other
> aspects of my iptables mucking things up, I have tried a very basic
> setup as follows:
>
>
> #/etc/sysconfig/iptables
>
> *mangle
> :PREROUTING ACCEPT [0:0]
> -A PREROUTING -p tcp --dport 23 -j TOS --set-tos 0x10
> :OUTPUT ACCEPT [0:0]
> :INPUT ACCEPT [0:0]
> :FORWARD ACCEPT [0:0]
> COMMIT
>
> *filter
> :OUTPUT ACCEPT [0:0]
> :INPUT ACCEPT [0:0]
> :FORWARD ACCEPT [0:0]
> COMMIT
>
> I can see that packets for telnet are being matched OK using:
>
> iptables -L -v -n -t mangle
>
> but the differentiated services field is still 0x00 when I capture
> packets in Ethereal !!
>
> I don't understand, but I hope I am just missing something silly.
> Please help me ;-)
>
> TIA
>
> Craig Jackson

DOh! I was looking at the traffic on the LAN with ethereal, instead of
looking at the traffic after the router !! The TOS bits are being set
fine.

One born every day....

Craig