length match problem

[Jackfritt <jackfritt@boh.de>]

Ok I have the following problem.

iptables -A OUTPUT -o ppp0 -p tcp -m length --length :40 -j MARK 
--set-mark 10

That should mark all ACK's or not ?

When I try to do this I get the error:

iptables: Invalid argument

I found out that this has something to do with the length match.
Because not used I don't get an error message. I looked around and found 
an example in netfilter-extensions-HOWTO with icmp:

iptables -A INPUT -p icmp --icmp-type echo-request -m length --length 
86:0xffff -j DROP

When I try to do something like this it doesn't work too :(

So now my question is what am I doin wrong ?

Sorry I'm not an iptables guy an I only tried a script from somewhere 
else. But this one line doesn't work.

anyone can help me ?


Thx


Joerg Esser