Why should I restrict OpenSSH access to my IP block?

Restricting OpenSSH access to your own IP block enhances security by blocking unauthorized connection attempts, reducing the risk of brute-force attacks and data breaches.

How does firewalling improve OpenSSH performance?

Firewalling reduces unwanted traffic to your server, decreasing load and increasing responsiveness, which results in better OpenSSH performance.

What happens if my IP address changes?

If your IP changes, your firewall rule may block your access. It's important to regularly update firewall rules or have a dynamic DNS setup to maintain remote access.

What backup access options should I have?

You should always have a backup access method like a secondary administrative account, VPN with a static IP, or a serial console (e.g., Oracle Cloud) in case of accidental lockout.

Are firewall rules enough to secure OpenSSH?

No. While firewalling is crucial, you should also update OpenSSH regularly, use key-based authentication, and monitor SSH logs for suspicious activity.

HiddenSSH - Secure OpenSSH Hardening

Firewall

Firewalling all traffic except the ones coming from your own IP block can greatly improve the security of your OpenSSH service and prevent unauthorized access.
By using firewall rules to restrict incoming traffic to only your own IP block, you can effectively block any attempts from outside the network to connect to your SSH service.
This helps to minimize the risk of attacks and data breaches.

In addition to improving security, firewalling can also improve the performance of your OpenSSH service.
By blocking unwanted traffic, you can reduce the amount of unnecessary network traffic and improve the speed and responsiveness of your service.

Firewall Server Level

To implement this firewall rule for OpenSSH, use a command-line tool such as iptables. Below is an example:

Iptables - INPUT/OUTPUT Chain is set to ACCEPT.

Create SSH ingress chain first:

iptables -A ssh-ingress -p tcp --dport 22 -j ACCEPT

Add the ssh-ingress chain to incoming traffic:

iptables -A ssh-ingress -j INPUT

Allow SSH traffic only from your IP block:

iptables -A INPUT -p tcp --dport ssh -s x.x.x.0/24 -j ACCEPT

Without this rule, iptables won't block any traffic:

iptables -A INPUT -p tcp --dport ssh -j DROP

Iptables - INPUT/OUTPUT Chain is set to DROP.

Create the SSH ingress chain:

iptables -A ssh-ingress -p tcp --dport 22 -j ACCEPT

Add the SSH ingress chain into incoming traffic:

iptables -A ssh-ingress -j INPUT

Allow SSH traffic from your IP block:

iptables -A INPUT -p tcp --dport ssh -s x.x.x.0/24 -j ACCEPT

When an iptables chain is set to DROP by default, it blocks all traffic unless explicitly allowed.
Without this rule, all SSH outgoing connections are denied.

iptables -A OUTPUT -m conntrack --ctstate ESTABLISHED -j ACCEPT

Firewall Subnet Level

Implementing a firewall rule is just one aspect of securing OpenSSH. It is also crucial to keep your OpenSSH software up-to-date, use public/private key authentication, and monitor logs for suspicious activity.

Firewall rules should be updated regularly to prevent getting locked out due to IP changes. If your IP address changes, updating firewall rules promptly is necessary to maintain remote access.

Having a backup access method is crucial in case of accidental lockout, such as using a secondary administrative account or like serial console in Oracle Cloud.