CONFIGURING A BASIC FIREWALL WITH UFW ON SLACKWARE


OVERVIEW

This document describes a minimal and explicit approach to configuring a
basic firewall on Slackware using UFW (Uncomplicated Firewall).

UFW provides a simplified interface for managing firewall rules while
still allowing direct backend customization when required. This setup
covers installation, basic rule management, enabling UFW at boot, and
optional NAT support for gateway scenarios.


DESIGN GOALS

- keep firewall rules simple and readable
- integrate cleanly with Slackware init scripts
- avoid unnecessary firewall management daemons
- support both workstation and gateway use cases
- retain full control over backend firewall behavior


ASSUMPTIONS

- Slackware 15.0 or Slackware-current is in use
- UFW is installed via SlackBuilds.org
- the user has root access
- basic networking is already functional


INSTALLING UFW

UFW is not part of the base Slackware distribution and must be installed
from SlackBuilds.org:

    https://slackbuilds.org/repository/15.0/network/ufw/


BASIC FIREWALL POLICY

A minimal workstation policy usually blocks incoming connections while
allowing outbound traffic:

    ufw default deny incoming
    ufw default allow outgoing


ADDING FIREWALL RULES

Allow basic services such as SSH, HTTP, and a custom TCP port:

    ufw allow SSH
    ufw allow WWW
    ufw allow 8080/tcp

Rules are added immediately but are not enforced until UFW is enabled.


ENABLING UFW ON SLACKWARE

Enable the firewall:

    ufw enable

Slackware uses /etc/rc.d/rc.firewall during system startup. To integrate
UFW with Slackware startup, replace rc.firewall with a symlink to
rc.ufw:

    ln -s /etc/rc.d/rc.ufw /etc/rc.d/rc.firewall

Ensure the UFW init script is executable:

    chmod 755 /etc/rc.d/rc.ufw

With this setup, UFW will be activated automatically at boot.


CHECKING FIREWALL STATUS

To view current firewall rules:

    ufw status

Example output:

    Status: active

    To                         Action      From
    --                         ------      ----
    SSH                        ALLOW       Anywhere
    WWW                        ALLOW       Anywhere
    SSH (v6)                   ALLOW       Anywhere (v6)
    WWW (v6)                   ALLOW       Anywhere (v6)

To view rules with numbering (useful for deletion):

    ufw status numbered


REMOVING FIREWALL RULES

List rules with numbers:

    ufw status numbered

Example:

    To                         Action      From
    --                         ------      ----
    SSH                        ALLOW       Anywhere
    WWW                        ALLOW       Anywhere
    8080/tcp                   ALLOW       Anywhere

Remove a rule by its number:

    ufw delete 2


NAT AND GATEWAY CONFIGURATION

UFW does not provide a high-level NAT command but supports NAT through
manual configuration. This is useful when the system acts as a gateway
or performs internet sharing.


ENABLING IP FORWARDING

Edit the UFW sysctl configuration file:

    vim /etc/ufw/sysctl.conf

Ensure the following line is enabled:

    net/ipv4/ip_forward=1

Apply the change immediately:

    sysctl -w net.ipv4.ip_forward=1


ADDING NAT RULES

Edit the UFW rules file:

    vim /etc/ufw/before.rules

Add the following near the top of the file, before the first *filter
section:

    *nat
    :POSTROUTING ACCEPT [0:0]

    # Replace eth0 with your external interface
    # (for example: enp1s0 or wlan0)
    -A POSTROUTING -s 192.168.0.0/24 -o eth0 -j MASQUERADE

    COMMIT

This configuration enables NAT for hosts in the 192.168.0.0/24 network
using the selected outbound interface.


RELOADING UFW

Apply the changes by restarting UFW:

    ufw disable
    ufw enable


CONCLUSION

UFW provides a practical and understandable firewall interface for
Slackware systems when combined with Slackware's native init scripts.

By enabling UFW explicitly, integrating it with rc.firewall, and
optionally configuring NAT through backend files, systems can be
secured without sacrificing transparency or control.


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Last Modified: 2026-05-09 20:05:00 UTC