Uncomplicated Firewall

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From the project home page:

Ufw stands for Uncomplicated Firewall, and is a program for managing a netfilter firewall. It provides a command line interface and aims to be uncomplicated and easy to use.

Installation

ufw can be installed from the official repositories.

Start ufw as systemd service to have it running and enable it to make it available after boot.

Basic configuration

A very simplistic configuration which will deny all by default, allow any protocol from inside a 192.168.0.1-192.168.0.255 LAN, and allow incoming Deluge and SSH traffic from anywhere:

# ufw default deny
# ufw allow from 192.168.0.0/24
# ufw allow Deluge
# ufw allow SSH

The next line is only needed once the first time you install the package:

# ufw enable

Then enable the ufw service with systemctl.

Finally, query the rules being applied via the status command:

# ufw status
Status: active
To                         Action      From
--                         ------      ----
Anywhere                   ALLOW       192.168.0.0/24
Deluge                     ALLOW       Anywhere
SSH                        ALLOW       Anywhere

The status report shows the rules added by the user. For most cases this will be what is needed, but it is good to be aware that builtin-rules do exist. These include filters to allow UPNP, AVAHI and DHCP replies. In order to see all rules setup

# ufw show raw 

may be used, as well as further reports listed in the manpage. Since these reports also summarize traffic, they may be somewhat difficult to read. Another way to check for accepted traffic:

# iptables -S | grep ACCEPT

While this works just fine for reporting, keep in mind not to enable the iptables service as long as you use ufw for managing it.

Note: If special network variables are set on the system in /etc/sysctl.d/*, it may be necessary to update /etc/ufw/sysctl.conf accordingly since this configuration overrides the default settings.

Adding other applications

The PKG comes with some defaults based on the default ports of many common daemons and programs. Inspect the options by looking in the /etc/ufw/applications.d directory or by listing them in the program itself:

# ufw app list

If users are running any of the applications on a non-standard port, it is recommended to simply make /etc/ufw/applications.d/custom containing the needed data using the defaults as a guide.

Warning: If users modify any of the PKG provided rule sets, these will be overwritten the first time the ufw package is updated. This is why custom app definitions need to reside in a non-PKG file as recommended above!

Example, deluge with custom tcp ports that range from 20202-20205:

[Deluge-my]
title=Deluge
description=Deluge BitTorrent client
ports=20202:20205/tcp

Should you require to define both tcp and udp ports for the same application, simply separate them with a pipe as shown: this app opens tcp ports 10000-10002 and udp port 10003:

ports=10000:10002/tcp|10003/udp

One can also use a comma to define ports if a range is not desired. This example opens tcp ports 10000-10002 (inclusive) and udp ports 10003 and 10009

ports=10000:10002/tcp|10003,10009/udp

Deleting applications

Drawing on the Deluge/Deluge-my example above, the following will remove the standard Deluge rules and replace them with the Deluge-my rules from the above example:

# ufw delete allow Deluge
# ufw allow Deluge-my

Query the result via the status command:

# ufw status
Status: active
To                         Action      From
--                         ------      ----
Anywhere                   ALLOW       192.168.0.0/24
SSH                        ALLOW       Anywhere
Deluge-my                  ALLOW       Anywhere

Rate limiting with ufw

ufw has the ability to deny connections from an IP address that has attempted to initiate 6 or more connections in the last 30 seconds. Users should consider using this option for services such as sshd.

Using the above basic configuration, to enable rate limiting we would simply replace the allow parameter with the limit parameter. The new rule will then replace the previous.

# ufw limit SSH
Rule updated
# ufw status
Status: active
To                         Action      From
--                         ------      ----
Anywhere                   ALLOW       192.168.0.0/24
SSH                        LIMIT       Anywhere
Deluge-my                  ALLOW       Anywhere

User rules

All user rules are stored in usr/lib/ufw/user.rules and usr/lib/ufw/user6.rules for IPv4 and IPv6 respectively.

Tips and tricks

Disable remote ping

Change ACCEPT to DROP in the following lines:

/etc/ufw/before.rules
# ok icmp codes
-A ufw-before-input -p icmp --icmp-type destination-unreachable -j ACCEPT
-A ufw-before-input -p icmp --icmp-type source-quench -j ACCEPT
-A ufw-before-input -p icmp --icmp-type time-exceeded -j ACCEPT
-A ufw-before-input -p icmp --icmp-type parameter-problem -j ACCEPT
-A ufw-before-input -p icmp --icmp-type echo-request -j ACCEPT

If you use IPv6, related rules are in /etc/ufw/before6.rules.

Disable UFW logging

Disabling logging may be useful to stop UFW filling up the kernel (dmesg) and message logs:

# ufw logging off

GUI frontends

Gufw

gufw is a GTK front-end for Ufw that aims to make managing a Linux firewall as accessible and easy as possible. It features pre-sets for common ports and p2p applications. It requires python, ufw, and GTK support.

kcm-ufw

kcm-ufwAUR is KDE4 control module for ufw. The following features are supported:

  • Enable/disable firewall
  • Configure firewall default settings
  • Add, edit, and remove rules
  • Re-order rules via drag'n'drop
  • Import/export of rules
  • Setting of some IP tables modules

The module will appear under "Network and Connectivity" category.

See also