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. Is there a forum for APF and other utilities? I see a forum when I search Google, but it appears to be restricted.

    Any way I have a problem with APF not starting correctly on OpenVZ with multiple IP addresses. venet0 is and venet0:0 and venet0:1 are the external IPs and APF comes up with errors on them. I don’t know whether the ethX:X/venetX:X syntax is affecting.

    Does it work with multiple IPs? IFACE_IN and IFACE_OUT appear to take single IPs only

    apf(20007): {glob} flushing & zeroing chain policies
    apf(20007): {glob} firewall offline
    apf(20043): {glob} activating firewall
    apf(20088): {glob} could not verify that interface venet0:0 is routed to a network, aborting.
    apf(20043): {glob} firewall initalized
    apf(20043): {glob} !!DEVELOPMENT MODE ENABLED!! – firewall will flush every 5 minutes.

  2. May I ask on where did you did nmap? If its in the same system then you will see the results its up. Please test it on a separate system.


    I recently installed APF . It appears installed properly. My aim is to Block port 25 on the server. However, after removing the port 25 from the config file, then i reloaded. But Port 25 is still OPEN. I confirmed this by running nmap, and port 25 is still open. Can someone tell me what might be wrong

  3. I recently installed APF . It appears installed properly. My aim is to Block port 25 on the server. However, after removing the port 25 from the config file, then i reloaded. But Port 25 is still OPEN. I confirmed this by running nmap, and port 25 is still open. Can someone tell me what might be wrong

  4. Hi,

    First of all, thank you for the great software you have created. It is one of our vital protection against outside threat.

    Currently we have an issue with IPV6. May I ask if APF can filter IPV6? doing an iptables -L shows all the rules loaded but when ip6tables -L is used then the output is:
    Chain INPUT (policy ACCEPT)
    target prot opt source destination

    Chain FORWARD (policy ACCEPT)
    target prot opt source destination

    Chain OUTPUT (policy ACCEPT)
    target prot opt source destination

    I guess there are no filter rules on ipv6. We are using ipv6 aware OS to public network.

    Please advice on how to enable ipv6 filtering.

    Thank you

  5. Hello
    I was wondering if it’s possible to use apf for a standalone pc connected to an untrusted lan , not necessarily intented to be used as a server , just for personal use


  6. Hi Ryan:

    I hope you and your family are doing well.

    When you get to updating APF, can you check how it can be made more user friendly on reboots when local dns (/etc/resolv.conf) may be broken?

    What we’ve seen is that if there are any local DNS resolution issues, APF can cause bootup to hang for an indefinite period of time.

    Thank you.

  7. hello all,

    was ddos´ed for 2 days now… apf + ddos-deflate seems to help!
    but, could anybody helping me, howto run my own firewall script and apf simultaneously?
    because my own firewall script is also kinda big and there some important dropes in it, so ive to get it running.
    thx for ya help!

    greetz mike

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