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Top Forums UNIX for Dummies Questions & Answers iptables to block port 25 only to a certain range Post 302897083 by Smiling Dragon on Thursday 10th of April 2014 10:35:42 PM
Old 04-10-2014
You just need to do the drop on all other port 25 outbound, also the NEW,ESTABLISHED thing doesn't really help you here as you want all types to work.
Code:
iptables -A OUTPUT -o eth0 -p tcp -d 1.2.3.0/24 --dport 25 -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --dport 25 -j DROP

I'd also suggest you leave off the -o eth0 too as you are trying to prevent outbound traffic in general, regardless of it's routing.

edit: According to the iptables help, you can actually specify negation - ie:
Code:
iptables -A OUTPUT -p tcp \! -d 1.2.3.0/24 --dport 25 -j DROP

Never tried this myself though so YMMV
 

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Firewall mark classifier in tc(8)				       Linux					 Firewall mark classifier in tc(8)

NAME
fw - fwmark traffic control filter SYNOPSIS
tc filter ... fw [ classid CLASSID ] [ action ACTION_SPEC ] DESCRIPTION
the fw filter allows to classify packets based on a previously set fwmark by iptables. If it is identical to the filter's handle, the fil- ter matches. iptables allows to mark single packets with the MARK target, or whole connections using CONNMARK. The benefit of using this filter instead of doing the heavy-lifting with tc itself is that on one hand it might be convenient to keep packet filtering and classifi- cation in one place, possibly having to match a packet just once, and on the other users familiar with iptables but not tc will have a less hard time adding QoS to their setups. OPTIONS
classid CLASSID Push matching packets to the class identified by CLASSID. action ACTION_SPEC Apply an action from the generic actions framework on matching packets. EXAMPLES
Take e.g. the following tc filter statement: tc filter add ... handle 6 fw classid 1:1 will match if the packet's fwmark value is 6. This is a sample iptables statement marking packets coming in on eth0: iptables -t mangle -A PREROUTING -i eth0 -j MARK --set-mark 6 SEE ALSO
tc(8), iptables(8), iptables-extensions(8) iproute2 21 Oct 2015 Firewall mark classifier in tc(8)
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