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Configuring a Service with Host Based Security Restrictions
Outside of using a Firewall, it is important to understsand that there are other methods of configuring a service with host based security restrictions. Using the hosts.allow and deny files, we will explore how TCP Wrappers works to secure our systems.
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Keep Client System from Connecting Over SSH
This is accomplished using the /etc/hosts.deny file (remember, if we try to allow specific locations, whatever is in /etc/hosts.allow will be applied first). You can accomplish this by making the following addition to the /etc/hosts.deny file:
Log All Connection Denials
Within the /etc/hosts.deny file, you will need to add the following in order to log connections:
sshd: 10.0.1.101 \ : spawn /bin/echo $(/bin/date) %a access denied >> /var/log/sshd \ :deny
Reload the SSH Service and Verify
You can reload (without disconnecting yourself) the SSH configuration via:
systemctl reload sshd
Then verify by trying to connect to the SERVER from the CLIENT system over SSH and viewing the denial message in /var/log/sshd.log
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