What is FireHOL?
FireHOL is... firewalling made easy:
transparent_squid 8080 "squid root" inface eth0 interface eth0 mylan policy accept interface ppp+ internet server smtp accept server http accept server ftp accept server ssh accept src example.firehol.org client all accept router mylan2internet inface eth0 outface ppp+ masquerade route all accept
FireHOL is an iptables firewall generator producing stateful iptables packet filtering firewalls, on Linux hosts and routers with any number of network interfaces, any number of routes, any number of services served, any number of complexity between variations of the services (including positive and negative expressions).
FireHOL is a language to express firewalling rules, not just a script that produces some kind of a firewall.
The goals of FireHOL are:
- Make firewalling an easy, straight forward task for everyone,
independently of the security skills he/she has.
FireHOL configuration files are very easy to type and read. To understand a complex firewall you will need just a few seconds.
Take a look bellow for an example configuration.
- Be as secure as possible by allowing explicitly only the wanted
traffic to flow.
FireHOL produces stateful rules for any service or protocol, in both directions of the firewall.
- Be a resource of knowledge around services and their peculiarities,
as far as firewalling is concerned.
Check the services list.
- Be open enough for any firewalling need. Although FireHOL is pre-configured for a large number of services, you can configure any service you like and FireHOL will turn it into a client, server, or a router.
- Be flexible enough to be used by end users and guru
administrators requiring extremely complex firewalls.
FireHOL configuration files are BASH scripts; you can write in them anything BASH accepts, including variables, pipes, loops, conditions, calls to external programs, run other BASH scripts with FireHOL directives in them, etc.
- Be simple to install on any modern Linux system; only one file is required, no compilations involved.
Is it secure?
FireHOL is secure because it has been designed with the right firewalling concept: deny everything, then allow only what is needed.
Also, FireHOL produces stateful iptables packet filtering firewalls (and possibly, the only generic tool today that does that for all services in both directions of the firewall).
Stateful means that traffic allowed to pass is part of a valid connection that has been initiated the right way. Stateful also means that you can have control based on who initiated the traffic. For example: you can choose to be able to ping anyone on the internet, but no one to be able to ping you. If for example you don't need to run a server on your Linux host, you can easily achieve a situation where you are able to do anything to anyone, but as far as the rest of world is concerned, you do not exist!
Learn another language?
FireHOL has been designed to allow you configure your firewall the same way you think of it. Its language is extremely simple. Basically you have to learn four commands:
- interface, to setup a firewall on a network interface
- router, to setup a firewall on traffic routed from one network interface to another
- server, to setup a listening service within an interface or router. The same command can be used as route within routers
- client, to setup a service client within an interface or router
Commands client and server have exactly the same syntax. A FireHOL interface has two mandatory arguments and a router has only one (and this is the same with one of the two interface requires). All the optional parameters are the same to all of them. This sounds like just one command is to be learned...
Of course there are a few more commands defined, but all of them exist just to give you finer control on these four.
If you don't believe it is simple, consider this example:
|I have a Linux host with two network interfaces.
|To the internet my Linux provides:
|My Linux is also a workstation, I want to run any client I wish.|
|My LAN is trusted.
If a server is running on my Linux I want my LAN PCs to use it.
|I would like my LAN PCs to use this Linux as a gateway for connecting, as clients, to the internet for all the services they wish.|
|My LAN PCs have private IPs, unroutable to the Internet.
I need to masquerade somehow their IP addresses for internet access.
This is it! The firewall is ready. I hope you have noticed that all the rules given match just one direction of the traffic: the request. They don't say anything about replies (see for example the src, inface or outface parameters). This is because FireHOL handles the replies automatically. You don't have to do anything about them: If a request is allowed, then the corresponding reply is also allowed. This also means that FireHOL produces the iptables statements to exactly match what is allowed in both directions and nothing more. If for example we remove the client all accept from the internet interface, our Linux will not be able to do anything with its PPP device except to send replies matching the server statements within this interface; no pings, no DNS, no web browsing, no nothing!
The complete configuration file (a little bit enriched) of the above example could be:
# Require release 5 of FireHOL configuration directives version 5 # A space separated list of all the IPs on the internet, I trust office="my-office-pc.example.com" # The IP address of this Linux and LAN for the rest of the world public_ip="198.51.100.1" # My LAN. Everything is allowed here. interface eth0 lan policy accept # The default is 'drop'. # Make sure the traffic coming in, comes from valid Internet IPs, # and that is targeting my public IP interface ppp+ internet src not "$UNROUTABLE_IPS" dst "$public_ip" # Protect me from various kinds of attacks. protection strong # Public servers. server smtp accept server http accept server ftp accept server ssh accept src "$office" # Make sure idents do not timeout. server ident reject with tcp-reset # This is also a workstation. client all accept # Route the LAN requests to the internet. router lan2internet inface eth0 outface ppp+ # Masquerading on outface. masquerade # Route all requests from inface to outface # and their replies back. route all accept
As an IT executive, responsible for many dozens of Linux systems, I needed a firewalling solution that would allow me and my team to have a clear and simple view of what is happening on each server, as far as firewalling is concerned. I also needed a solution that will allow my team members to produce high quality and homogeneous firewalls independently of their security skills and knowledge. After searching for such a tool, I quickly concluded that no tool is flexible, open, easy, and simple enough for what I needed.
I decided to write FireHOL in a way that will allow me, or anyone else, to view, verify and audit the firewall of any Linux server or Linux router in seconds. FireHOL's configuration is extremely simple... you don't have to be an expert to design a complicated but secure firewall.
What features does it have?
FireHOL handles firewalls protecting one host on all its interfaces and any combination of stateful firewalls routing traffic from one interface to another. There are no limitations on the number of interfaces or on the number of routing routes (except the ones iptables has, if any).
FireHOL, still lacks a few features: QoS for example is not supported directly. You are welcome to extend FireHOL and send me your patches to integrate within FireHOL. In any case however, you can embed normal iptables commands in a FireHOL configuration to do whatever iptables supports.
Since FireHOL produces stateful commands, for every supported service it needs to know the flow of requests and replies. Today FireHOL supports the following services:
- Many single socket protocols, such as HTTP, NNTP, SMTP, POP3, IMAP4, RADIUS, SSH, LDAP, MySQL, Telnet, NTP, DNS, etc. There are a few dozens of such services defined in FireHOL. Check this list. Even if something is missing, you can define it.
- Many complex protocols, such as FTP, NFS, SAMBA, PPTP, etc. If you need some complex protocol that is not present, you will have to program it (in simple BASH scripting - there are many commented examples on how this is done). Again, you will just create one BASH function with the rules of the protocol, and FireHOL will turn it to a client, a server or a router.