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