Ubuntu Firewall : How to open ssh port using ufw on Ubuntu/Debian Linux

How to open ssh port using ufw on Ubuntu/Debian Linux

How do I allow incoming SSH connections from a specific IP address or subnet on a Ubuntu or Debian Linux server using ufw?

UFW is an acronym for uncomplicated firewall. It is used for managing a Linux firewall and aims to provide an easy to use interface for the user. In this tutorial, you will learn how to use UFW a frontend to iptables for opening incoming SSH connection on Ubuntu Linux 16.04 LTS or Debian Linux server.

Fig.01: Allow Incoming SSH from Specific IP Address or Subnet

Open incoming SSH port for all

The syntax is:
sudo ufw allow ssh
OR
$ sudo ufw allow 22/tcp
If you are running ssh on TCP port # 2222, enter:
$ sudo ufw allow 2222/tcp

How to allow incoming SSH from specific IP address

The syntax is:
$ sudo ufw allow from {IP_ADDRESS_HERE} to any port 22
To allow incoming SSH connections from a specific IP address named 202.54.1.1, enter:
$ sudo ufw allow from 202.54.1.1 to any port 22

How to allow incoming SSH from specific subnets

The syntax is:
$ sudo ufw allow from {IP_SUB/net} to any port 22
To allow incoming SSH connections from a specific IP subnet named 202.54.1.1/29, enter:
$ sudo ufw allow from 202.54.1.1/29 to any port 22

Limit incoming SSH port for all

Open incoming SSH but deny connections from an IP address that has attempted to initiate 6 or more connections in the last 30 seconds. The syntax is:
$ sudo ufw limit ssh
OR
$ sudo ufw limit 22/tcp

How to check the status of ufw

The syntax is:
$ sudo ufw status
Sample outputs:

Status: active

To                         Action      From
--                         ------      ----
22                         ALLOW       Anywhere                  
72.14.190.12 443/tcp       ALLOW       Anywhere                  
72.14.190.12 80/tcp        ALLOW       Anywhere                  

if ufw was not enabled the output would be:

sudo ufw status
Status: inactive

To turn on UFW on with the default set of rules including open SSH port, enter:
$ sudo ufw enable
$ sudo ufw status verbose

How to limit SSH (TCP port 22) connections with ufw on Ubuntu Linux

How do I limit ssh connection attempts using UFW (Uncomplicated Firewall) on Ubuntu or Debian Linux server?

UFW means Uncomplicated Firewall. It defaults on Ubuntu and can be installed on other Linux distros such as Arch Linux, Debian and more. It is nothing but a front-end for managing a Netfilter firewall. It provides a command line interface and aims to be uncomplicated and easy to use.

Rate limiting with ufw

You can add limit rule. Currently only IPv4 is supported. With this syntax you can deny connections from an IP address that has attempted to initiate 6 or more connections in the last 30 seconds. This option is very useful for services such as sshd.

Syntax

The syntax is pretty simple:

## ufw limit ssh various usage ## ufw limit ssh   ufw limit ssh/tcp   ufw limit ssh comment 'Rate limit for openssh serer'   ### if sshd is running on tcp port 2022 #### ufw limit 2022/tcp comment 'SSH port rate limit'

The above rules are useful for protecting against brute-force login attacks. When a limit rule is used, ufw will normally allow the connection but will deny connections if an IP address attempts to initiate six or more connections within thirty seconds. Once setup you can verify it with the following command:
$ sudo ufw limit ssh/tcp comment 'Rate limit for openssh serer'
$ sudo ufw status
Sample outputs:

Status: active

To                         Action      From
--                         ------      ----
22/tcp                     LIMIT       Anywhere                   # Rate limit for openssh serer
22/tcp (v6)                LIMIT       Anywhere (v6)              # Rate limit for openssh serer

The actual rules are as follows in iptables:

-A ufw-user-input -p tcp -m tcp --dport 22 -m conntrack --ctstate NEW -m recent --set --name DEFAULT --mask 255.255.255.255 --rsource -A ufw-user-input -p tcp -m tcp --dport 22 -m conntrack --ctstate NEW -m recent --update --seconds 30 --hitcount 6 --name DEFAULT --mask 255.255.255.255 --rsource -j ufw-user-limit -A ufw-user-input -p tcp -m tcp --dport 22 -j ufw-user-limit-accept

Please note that the new ssh rule will then replace the previous ssh rule.