ufw is the friendly command line firewall utility in Debian and Ubuntu.
I’ll show you how to create a specific rule syntax for allowing traffic in from a specific ip on a specific port.
Say for example you want to allow traffic from 192.168.1.215 on udp port 88.
Here is the command:
$ sudo ufw allow from 192.168.1.215 proto udp to any port 88
You can view your current rules with:
$ sudo ufw status
Status: active To Action From -- ------ ---- 88/udp ALLOW 192.168.1.215
To delete this rule, preface the command with delete:
$ sudo ufw delete allow from 192.168.1.215 proto udp to any port 88