Is your policy accept? It is possible to trace the packet through the netfilter path by setting up raw table rules with TRACE as the target and logging turned on (search the web for details - probably too much to post here) but be aware that you need a very controlled test because the syslog entries will likely be an order of magnitude greater than the actual packet count.
________________________________ From: CentOS centos-bounces@centos.org on behalf of david david@daku.org Sent: Tuesday, June 16, 2020 2:21 PM To: CentOS mailing list centos@centos.org Subject: [EXTERNAL] [CentOS] firewall help request
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Folks
I'm struggling with my firewall settings, and would appreciate some help.
I have a gateway machine (currently Centos 7 with IPV4 only) with two NICs. One is connected to the internet, the other to an internal network (10.0.0.0/24) of mixed hardware (windows7, android tablets, android phones, linux boxes) using NAT. I wish to block all outgoing connects to any external IP address on port 22 (ssh) originating from any internal machine except one (which has a known internal IP address).
I've tried some commands using 'iptables' to accomplish this, but so far have failed. If anyone has a suggestion, I'd really appreciate it. In addition, a suitable version for 'firewalld' could be useful, as an upgrade to Centos 8 is in plan.
Examples of what I've tried, and then tested. None of them stopped an outgoing SSH from an internal system.
iptables -I INPUT -p tcp --dport 22 -s 10.0.0.0/24 -j DROP iptables -I INPUT -p tcp --dport 22 -s 10.0.0.0/24 -j DROP
Much thanks
David
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