Universal Configuration

Tom Eastep

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover, and with no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License.

2016/02/19


Configuring Shorewall

Once you have installed the Shorewall software, you must configure it. The easiest way to do that is to use one of Shorewall's Sample Configurations. The Universal Configuration is one of those samples.

What the Universal Configuration does

The Universal Shorewall configuration requires that you simply copy the configuration to /etc/shorewall and start Shorewall. This sample configuation:

  • Allows all outgoing traffic.

  • Blocks all incoming connections except:

    • Secure Shell

    • Ping

  • Allows forwarding of traffic, provided that the system has more than one interface or is set up to route between networks on a single interface.

How to Install it

The location of the sample configuration files is dependent on your distribution and how you installed Shorewall.

  1. If you installed using an RPM, the samples will be in the Samples/Universal subdirectory of the Shorewall documentation directory. If you don't know where the Shorewall documentation directory is, you can find the samples using this command:

    ~# rpm -ql shorewall-common | fgrep Universal
    /usr/share/doc/packages/shorewall/Samples/Universal
    /usr/share/doc/packages/shorewall/Samples/Universal/interfaces
    /usr/share/doc/packages/shorewall/Samples/Universal/policy
    /usr/share/doc/packages/shorewall/Samples/Universal/rules
    /usr/share/doc/packages/shorewall/Samples/Universal/zones
    ~#
  2. If you installed using the tarball, the samples are in the Samples/Universal directory in the tarball.

  3. If you installed using a Shorewall 4.x .deb, the samples are in /usr/share/doc/shorewall-common/examples/Universal.. You do not need the shorewall-doc package to have access to the samples.

Simple copy the files from the Universal directory to /etc/shorewall.

How to Start the firewall

Before starting Shorewall for the first time, it's a good idea to stop your existing firewall. On Redhat/CentOS/Fedora, at a root prompt type:

service iptables stop

If you are running SuSE, use Yast or Yast2 to stop SuSEFirewall.

Once you have Shorewall running to your satisfaction, you should totally disable your existing firewall. On /Redhat/CentOS/Fedora:

chkconfig --del iptables

At a root prompt, type:

/sbin/shorewall start

That's it. Shorewall will automatically start again when you reboot.

Now that it is running, ...

How do I stop the firewall?

At a root prompt, type:

/sbin/shorewall clear

The system is now 'wide open'.

How do I prevent it from responding to ping?

Edit /etc/shorewall/rules and remove the line that reads:

Ping(ACCEPT) net $FW

and at a root prompt, type:

/sbin/shorewall restart

How do I allow other kinds of incoming connections?

Shorewall includes a collection of macros that can be used to quickly allow or deny services. You can find a list of the macros included in your version of Shorewall using the command ls /usr/share/shorewall/macro.* or at a shell prompt type:

/sbin/shorewall show macros

If you wish to enable connections from the Internet to your firewall and you find an appropriate macro in /etc/shorewall/macro.*, the general format of a rule in /etc/shorewall/rules is:

#ACTION         SOURCE    DESTINATION     PROTO       DPORT
<macro>(ACCEPT) net       $FW

Important

Be sure to add your rules after the line that reads SECTION NEW.

Example 1. You want to run a Web Server and a IMAP Server on your firewall system:

#ACTION     SOURCE    DESTINATION     PROTO       DPORT
Web(ACCEPT) net       $FW
IMAP(ACCEPT)net       $FW

You may also choose to code your rules directly without using the pre-defined macros. This will be necessary in the event that there is not a pre-defined macro that meets your requirements. In that case the general format of a rule in /etc/shorewall/rules is:

#ACTION   SOURCE    DESTINATION     PROTO       DPORT
ACCEPT    net       $FW             <protocol>  <port>

Example 2. You want to run a Web Server and a IMAP Server on your firewall system:

#ACTION   SOURCE    DESTINATION     PROTO       DPORT
ACCEPT    net       $FW             tcp          80
ACCEPT    net       $FW             tcp          143

If you don't know what port and protocol a particular application uses, see here.

How do I make the firewall log a message when it disallows an incoming connection?

Shorewall does not maintain a log itself but rather relies on your system's logging configuration. The following commands rely on knowing where Netfilter messages are logged:

  • shorewall show log (Displays the last 20 Netfilter log messages)

  • shorewall logwatch (Polls the log at a settable interval

  • shorewall dump (Produces an extensive report for inclusion in Shorewall problem reports)

It is important that these commands work properly because when you encounter connection problems when Shorewall is running, the first thing that you should do is to look at the Netfilter log; with the help of Shorewall FAQ 17, you can usually resolve the problem quickly.

The Netfilter log location is distribution-dependent:

  • Debian and its derivatives log Netfilter messages to /var/log/kern.log.

  • Recent SuSE/OpenSuSE™ releases come preconfigured with syslog-ng and log netfilter messages to /var/log/firewall.

  • For other distributions, Netfilter messages are most commonly logged to /var/log/messages.

Modify the LOGFILE setting in /etc/shorewall/shorewall.conf to specify the name of your log.

Important

The LOGFILE setting does not control where the Netfilter log is maintained -- it simply tells the /sbin/shorewall utility where to find the log.

Now, edit /etc/shorewall/policy and modify the line that reads:

net all DROP

to

net all DROP info

Then at a root prompt, type:

/sbin/shorewall reload

How do I prevent the firewall from forwarding connection requests?

Edit /etc/shorewall/interfaces, and remove the routeback option from the interface. e.g., change the line that reads:

net all - dhcp,physical=+,routeback,optional

to

net all - dhcp,physical=+,optional

Then at a root prompt, type:

/sbin/shorewall reload

Documentation


Frequently Used Articles

- FAQs - IPv4 Manpages - IPv6 Manpages - Configuration File Basics - Beginner Documentation - Troubleshooting

Shorewall 4.4/4.5/4.6 Documentation

Shorewall 4.0/4.2 Documentation


Shorewall 5.0 HOWTOs and Other Articles

- 6to4 and 6in4 Tunnels - Accounting - Actions - Aliased (virtual) Interfaces (e.g., eth0:0) - Anatomy of Shorewall - Anti-Spoofing Measures - AUDIT Target support - Bandwidth Control - Blacklisting/Whitelisting - Bridge/Firewall - Building Shorewall from GIT - Commands - Compiled Programs - Configuration File Basics - DHCP - DNAT - Dynamic Zones - ECN Disabling by host or subnet - Events - Extension Scripts - Fallback/Uninstall - FAQs - Features - Fool's Firewall - Forwarding Traffic on the Same Interface - FTP and Shorewall - Helpers/Helper Modules - Installation/Upgrade - IPP2P - IPSEC - Ipsets - IPv6 Support - ISO 3661 Country Codes - Kazaa Filtering - Kernel Configuration - KVM (Kernel-mode Virtual Machine) - Limiting Connection Rates - Linux Containers (LXC) - Linux-vserver - Logging - Macros - MAC Verification - Manpages (IPv4) (IPv6) - Manual Chains - Masquerading - Multiple Internet Connections from a Single Firewall - Multiple Zones Through One Interface - My Shorewall Configuration - Netfilter Overview - Network Mapping - No firewalling of traffic between bridge port - One-to-one NAT - Operating Shorewall - OpenVPN - OpenVZ - Packet Marking - Packet Processing in a Shorewall-based Firewall - 'Ping' Management - Port Forwarding - Port Information - Port Knocking (deprecated) - Port Knocking, Auto Blacklisting and Other Uses of the 'Recent Match' - PPTP - Proxy ARP - QuickStart Guides - Release Model - Requirements - Routing and Shorewall - Routing on One Interface - Samba - Shorewall Events - Shorewall Init - Shorewall Lite - Shorewall on a Laptop - Shorewall Perl - Shorewall Setup Guide - SMB - SNAT - Split DNS the Easy Way - Squid with Shorewall - Starting/stopping the Firewall - Static (one-to-one) NAT - Support - Tips and Hints - Traffic Shaping/QOS - Simple - Traffic Shaping/QOS - Complex - Transparent Proxy - UPnP - Upgrade Issues - Upgrading to Shorewall 4.4 (Upgrading Debian Lenny to Squeeze) - VPN - VPN Passthrough - White List Creation - Xen - Shorewall in a Bridged Xen DomU - Xen - Shorewall in Routed Xen Dom0

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