Advanced Policy Firewall

Current Release:

Advanced Policy Firewall (APF) is an iptables(netfilter) based firewall system designed around the essential needs of today’s Internet deployed servers and the unique needs of custom deployed Linux installations. The configuration of APF is designed to be very informative and present the user with an easy to follow process, from top to bottom of the configuration file.

The technical side of APF is such that it utilizes the latest stable features from the iptables (netfilter) project to provide a very robust and powerful firewall. The filtering performed by APF is three fold:
1) Static rule based policies (not to be confused with a “static firewall”)
2) Connection based stateful policies
3) Sanity based policies

The first, static rule based policies, is the most traditional method of firewalling. This is when the firewall has an unchanging set of instructions (rules) on how traffic should be handled in certain conditions. An example of a static rule based policy would be when you allow/deny an address access to the server with the trust system or open a new port with conf.apf. So the short of it is rules that infrequently or never change while the firewall is running.

The second, connection based stateful policies, is a means to distinguish legitimate packets for different types of connections. Only packets matching a known connection will be allowed by the firewall; others will be rejected. An example of this would be FTP data transfers, in an older era of firewalling you would have to define a complex set of static policies to allow FTA data transfers to flow without a problem. That is not so with stateful policies, the firewall can see that an address has established a connection to port 21 then “relate” that address to the data transfer portion of the connection and dynamically alter the firewall to allow the traffic.

The third, sanity based policies, is the ability of the firewall to match various traffic patterns to known attack methods or scrutinize traffic to conform to Internet standards. An example of this would be when a would-be attacker attempts to forge the source IP address of data they are sending to you, APF can simply discard this traffic or optionally log it then discard it. To the same extent another example would be when a broken router on the Internet begins to relay malformed packets to you, APF can simply discard them or in other situations reply to the router and have it stop sending you new packets (TCP Reset).

– detailed and well commented configuration file
– granular inbound and outbound network filtering
– user id based outbound network filtering
– application based network filtering
– trust based rule files with an optional advanced syntax
– global trust system where rules can be downloaded from a central management server
– reactive address blocking (RAB), next generation in-line intrusion prevention
– debug mode provided for testing new features and configuration setups
– fast load feature that allows for 1000+ rules to load in under 1 second
– inbound and outbound network interfaces can be independently configured
– global tcp/udp port & icmp filtering with multiple filters (drop, reject, prohibit)
– configurable policies for each ip on the system with convenience variables to import settings
– packet flow rate limiting that prevents abuse on the most widely abused protocol, icmp
– prerouting and postrouting rules for optimal network performance
– block list support to ban networks exhibiting suspicious activity
– spamhaus Don’t Route Or Peer List support to ban known “hijacked zombie” IP blocks
– any number of additional interfaces may be configured as trusted or untrusted
– additional firewalled interfaces can have there own unique firewall policies applied
– intelligent route verification to prevent embarrassing configuration errors
– advanced packet sanity checks to make sure traffic coming and going meets the strictest of standards
– filter attacks such as fragmented UDP, port zero floods, stuffed routing, arp poisoning and more
– configurable type of service options to dictate the priority of different types of network traffic
– intelligent default settings to meet every day server setups
– dynamic configuration of your servers local DNS revolvers into the firewall
– optional filtering of common p2p applications
– optional filtering of private & reserved IP address space
– optional implicit blocks of the ident service
– configurable connection tracking settings to scale the firewall to the size of your network
– configurable kernel hooks (ties) to harden the system further to syn-flood attacks & routing abuses
– advanced network control such as explicit congestion notification and overflow control
– helper chains for FTP DATA and SSH connections to prevent client side issues
– optional rate limited event logging
– logging subsystem that allows for logging data to user space programs or standard syslog files
– comprehensive logging of every rule added
– detailed startup error checking
– if you are familiar with netfilter you can create your own rules in any of the policy files
– pluggable and ready advanced use of QoS algorithms provided by the Linux
– 3rd party add-on projects that compliment APF features

Funding for the continued development and research into this and other projects is solely dependent on public contributions and donations. If this is your first time using this software we ask that you evaluate it and consider a small donation; for those who frequent and are continued users of this and other projects we also ask that you make an occasional donation to help ensure the future of our public projects.

236 Replies to “Advanced Policy Firewall”

  1. Ubuntu has old version of APF in its repositories and strange ways of changing names of files and directories during the installation with apt-get. So I followed instructions on to install the current version of APF on Ubuntu. But instead of modifying the APF files I have symlinked /etc/rc.d/init.d with /etc/init.d. So hence my two questions:

    1) Is it ok to symlink like this or do I really have to change paths inside of files?

    2) Running update-rc.d apf defaults gives:

    update-rc.d: warning: /etc/init.d/apf missing LSB information

    Is it ok to ignore it or I have to change something?

    Generally, it would be nice if install script was adopted to run under Ubuntu, since currently it is confused with paths. I tested on CentOS installation script runs fine, but on Ubuntu it aborts since can’t find files.

  2. On CentOS 5.8 we are seeing the following error in our logs as it relates to APF:

    ” Mar 9 04:08:01 cp crond[7331]: CRON: error in (/etc/cron.d/refresh.apf) problem is (bad minute)”

    Rather than using */480 in the minute mark, why not use */8 in the hour mark?

    Thank you.

    1. I’m get the same error. How did you correct it? Thanks.

      My refresh.apf file is below.

      */10 * * * * root /etc/apf/apf –refresh >> /dev/null 2>&1 &

    2. Same problem with CentOS 5.8. cron_refresh () in internals/functions.apf uses */$SET_REFRESH. Would changing that to 0-59/$SET_REFRESH fix the issue?

  3. May I ask for a programming change to internals/functions.apf where you would add the following as part of the option string for wget?


    $WGET –bind-address=$NET -t 1 -T 4 $GD_URL_PROT://$GD_URL >> /dev/null 2>&1

    That way providers who are limiting access for say the global trust service can rely on the wget’s coming from the primary network card IP rather than a different IP.

    Thank you!

    1. I’ll get this into the next update of APF along with some of your more recent contributed changes, thanks as always Peter for being a loyal and long time supporter of my projects.

  4. Odin K.:

    I couldn’t find anything in the docs or the changelog regarding IPv6 support, save for a one year old comment that promised it to be implemented in the “near future”. So what’s the current status of IPv6 support?

    I am about to install a new system.

    I have been an ardent supporter of apf for 3 years now, but I want to make sure that my new system will handle ipv6.

    I saw 1-year-old comment from Ryan on this forum saying ipv6 would be addressed “in the very near future”.

    Is there a timetable for ipv6 capability in apf? If so, when? If ipv6 support will be added, will I be able to just upgrade an existing install or will I need to rip and replace?

    A quick reply would be appreciated


    1. I do not have an ETA on full ipv6 support for APF however since APF is simply an iptables wrapper, it should not be a terribly complicated process to implement. This is something I will put time into as soon as possible.

      1. Please do. I have a number of systems with IPv6 addresses and as a result, are completely exposed. IPv6 support would be very much welcomed!

  5. Hi,
    APF won’t work (start) with a kernel above 2.6 … I installed the debian paket (apt-firewall) but it then won’t download the rules because starting with “/usr/local/sbin/apf -s” won’t work.

    thanks for the good work!


  6. Hi,
    I am getting attack on apache doc root, and attacker is changing their IP-address randomly. is their any option to block attacker via using his MAC address.

    1. You can only filter by mac addresses for traffic inside your own network, as all public internet traffic will have the mac address of your local router/switch.

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