Asst with IPTABLES

dutch1918 · 12-19-2006, 07:07 AM

I want to block port 25 from 192.168.182.0/24. Would I use :

Code:

iptables -I FORWARD 2 -s 192.168.182.0/24 -p tcp --dport 25 -j DROP

or should it be

Code:

iptables -I FORWARD 2 -s 192.168.182.0/24 -d anywhere -p tcp --dport 25 -j DROP

amitsharma_26 · 12-19-2006, 07:35 AM

Look.. first, both of these two commands are absolutely equivalent. As in first case, -in the absence of -d, it would take it as anywhere itself.

Second, Just for the information part, while you run these block rules at FORWARD chain, you cant block packets for your own box.

int0x80 · 12-19-2006, 11:14 PM

This should do:

Code:

iptables -I INPUT -s 192.168.182.0/24 -p tcp --dport 25 -j DROP

For debugging, you could:
1. Check output from iptables -nvL
2. Start a sniffer and use -j REJECT instead of -j DROP
3. Use the -j LOG target in conjunction with another chain

Matir · 12-19-2006, 11:27 PM

If you want to block packets either that will be forwarded OR that will be destined for your box, there are two ways to do that:

Code:

iptables -t nat -I PREROUTING -s 192.168.182.0/24 -p tcp --dport 25 -j DROP

or

Code:

iptables -I FORWARD -s 192.168.182.0/24 -p tcp --dport 25 -j DROP
iptables -I INPUT -s 192.168.182.0/24 -p tcp --dport 25 -j DROP

The first one is more concise, but many people argue against doing filtering in the nat table (hence the filter table).

dutch1918 · 12-20-2006, 07:26 AM

Actually I guess I should had clarified that I am using a Wifi Hotspot on a Linksys router were I want to block port 25. Anyway I got it working and thanks for everyones input.