UFW (Uncomplicated Firewall) is a front-end for iptables and is particularly well-suited for a single server or host-based firewalls. It is the default firewall configuration tool for Ubuntu Linux. The UFW developed for a new sysadmin with ease use in mind. It is a user-friendly way to create an IPv4 or IPv6 based firewall to protect the server.
ufw block specific IP address
The syntax is:
sudo ufw deny from {ip-address-here} to any
To block or deny all packets from 192.168.1.5, enter:
sudo ufw deny from 192.168.1.5 to any
Show firewall status including your rules
Verify newly added rules, enter:
$ sudo ufw status numbered
OR
$ sudo ufw status
ufw block specific IP and port number
The syntax is:
ufw deny from {ip-address-here} to any port {port-number-here}
To block or deny spammers IP address 202.54.1.5 to port 80, enter:
sudo ufw deny from 202.54.1.5 to any port 80
Again verify with the following command:
$ sudo ufw status numbered
Sample outputs:
Status: active To Action From -- ------ ---- [ 1] 192.168.1.10 80/tcp ALLOW Anywhere [ 2] 192.168.1.10 22/tcp ALLOW Anywhere [ 3] Anywhere DENY 192.168.1.5 [ 4] 80 DENY IN 202.54.1.5 |
ufw deny specific IP, port number, and protocol
The syntax is:
sudo ufw deny proto {tcp|udp} from {ip-address-here} to any port {port-number-here}
For example block hacker IP address 202.54.1.1 to tcp port 22, enter:
$ sudo ufw deny proto tcp from 202.54.1.1 to any port 22
$ sudo ufw status numbered
ufw block subnet
The syntax is same:
$ sudo ufw deny proto tcp from sub/net to any port 22
$ sudo ufw deny proto tcp from 202.54.1.0/24 to any port 22
How do I delete blocked IP address or unblock an IP address again?
The syntax is:
$ sudo ufw status numbered
$ sudo ufw delete NUM
To delete rule number # 4, enter:
$ sudo ufw delete 4
Sample outputs:
Deleting:
deny from 202.54.1.5 to any port 80
Proceed with operation (y|n)? y
Rule deletedTip: UFW NOT blocking an IP address
UFW (iptables) rules are applied in order of appearance, and the inspection ends immediately when there is a match. Therefore, for example, if a rule is allowing access to tcp port 22 (say using sudo ufw allow 22), and afterward another Rule is specified blocking an IP address (say using ufw deny proto tcp from 202.54.1.1 to any port 22), the rule to access port 22 is applied and the later rule to block the hacker IP address 202.54.1.1 is not. It is all about the order. To avoid such problem you need to edit the /etc/ufw/before.rules file and add a section to “Block an IP Address” after “# End required lines” section.
$ sudo vi /etc/ufw/before.rules
Find line that read as follows:
# End required lines
Append your rule to block spammers or hackers:
# Block spammers -A ufw-before-input -s 178.137.80.191 -j DROP # Block ip/net (subnet) -A ufw-before-input -s 202.54.1.0/24 -j DROP |
Save and close the file. Finally, reload the firewall:
$ sudo ufw reload
3 comment
Simple indeed. I’m still a fanboy of core commands because any command wrapper could be a target of potential attacker and altering a python3 script seem to be much easier than altering a binary.
How would you block the whole AS address space for a given AS the easiest way?
ufw insert 1 deny from {IP}will insert the rule at the top, so you do not need to edit the `before.rules`
You probably want to use
ufw insert 1 reject from {IP}
Rationale: “insert 1” is required to avoid having earlier rule allowing the connection. “reject” instead of “deny” makes it look like the port has been closed instead of looking like dropped packages.