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@xxxxxxxxxx> on behalf of david <david@xxxxxxxx>
Sent: Tuesday, June 16, 2020 2:21 PM
To: CentOS mailing list <centos@xxxxxxxxxx>
Subject: [EXTERNAL] firewall help request
CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you recognize the sender and know the content is safe.
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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Leroy Tennison
Network Information/Cyber Security Specialist
E: leroy@xxxxxxxxxxxxxxxx
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