Re: Why is this not working???

[Aj Mirani <debsec@tucows.com>]

Why not put something like this into your INPUT chain:

-A INPUT -p tcp -m tcp --dport 22 -s xxx.xxx.xxx.xxx/28 -d yyy.yyy.yyy.yyy -j ACCEPT

Also for your line: 
-A INPUT -p tcp --syn -m limit --limit 5/s -i eth0 -j ACCEPT

This is a server wide limit not a per host limit which depending on what
you're trying to prevent may not be the best way to do it.

If you are trying to prevent a syn attack but still want the server to
respond to legitimate requests try something like this:
-A INPUT -p tcp -m tcp --tcp-flags SYN,RST,ACK SYN -m recent --set --name SYNATTACK --rsource 
-A INPUT -p tcp -m tcp --tcp-flags SYN,RST,ACK SYN -m recent --update --seconds 20 --hitcount 10 --name SYNATTACK --rsource -j DROP 
-A INPUT -p tcp -m tcp --tcp-flags SYN,RST,ACK SYN -j ACCEPT 

This dynamically put hosts on a 'blacklist' who are trying to connect
too fast (more that 10 times in a 20 second period.)  with the use of
--update it will keep them blacklisted as long as they continue to send
packets too fast.



On Tue, Apr 25, 2006 at 04:14:59PM +0300, Stratos Margaritis wrote:
> Can someone help me find out why is this rule does not work?
> 
> *filter
> :INPUT DROP [1803:271102]
> :FORWARD DROP [0:0]
> :OUTPUT DROP [0:0]
> -A INPUT -i lo -j ACCEPT
> -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
> -A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
> -A INPUT -p tcp -m tcp --dport 25 -j ACCEPT
> -A INPUT -p tcp -m tcp --dport 53 -j ACCEPT
> -A INPUT -p udp -m udp --dport 53 -j ACCEPT
> -A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
> -A INPUT -p icmp -j ACCEPT
> -A INPUT -p tcp -j REJECT --reject-with tcp-reset
> -A INPUT -p tcp --syn -m limit --limit 5/s -i eth0 -j ACCEPT
> -A FORWARD -p tcp -i eth0 -s xxx.xxx.xxx.xxx/28 -o eth1 -d yyy.yyy.yyy.yyy -j 
> ACCEPT
> -A FORWARD -j LOG
> 
> Where xxx.xxx.xxx.xxx is a real network that should be allowed to contact the 
> server yyy.yyy.yyy.yyy both of which are having real IP's.
> 
> 
> -- 
> Stratos
> stratism@gmail.com



-- 
Aj Mirani
Network Operations
Tucows.com Inc