How to block/deny SSH connection to server using /etc/hosts.deny file?

Secure Shell protocol is abbreviated as SSH. It is a secure and most commonly using protocol to access remote servers. This protocol uses encryption while transferring data between two hosts.

TCP Wrapper is a host-based networking ACL system, used to filter network access to Internet Protocol servers on (Unix-like) operating systems such as Linux or BSD.

It allows host or subnetwork IP addresses, names and/or ident query replies, to be used as tokens on which to filter for access control purposes.

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I am going to explain how TCP wrappers help to protect server by controlling external connections. We can control the SSH connection to a server by using the following files:

/etc/hosts.allow and /etc/hosts.deny

How to block an IP address from SSH connection?

Step 1 : SSH to server as root user.
Step 2 : Open /etc/hosts.deny file using your favorite text editor.

sshd : IP-Address

To block more than one IP addresses:

sshd : IP-Address1, IP-Address2, IP-Address3

To block IP ranges:

sshd : 33.*.*.*
sshd : 66.66.*.*

Block all IP addresses from SSH

sshd : ALL

Or

ALL : ALL

SSH connection result:

[root@localhost ~]# ssh localhost
ssh_exchange_identification: Connection closed by remote host

We can also control the same from /etc/hosts.allow file by adding the keyword “DENY.”

# vi /etc/hosts.allow

sshd : ALL : DENY

Related Links:

How to manage SSH permission for custom users under your server
How to create a banner/welcome-note for SSH server
How to disable SSH login as root user – PermitRootLogin
/etc/hosts.allow