The Internet is a big, scary place, and so we must protect our small business networks with strong, reliable firewalls. So here is the list of all the Top Linux firewall

1. As in Today's Era where nothing can go easily without the help of Internet. That is
from a small Business to a Large Multinational Network work, all relies on the
Internet Today. So Vice versa all of our important data, information etc are available
easily to be accessed out. Thus in order to protect our small Business network from
the reach of spammers and being threaten we must have a Strong Firewall.
Firewalls can range from a simple gadget that keeps bad data packets out of
networks to sophisticated multi-function gateways.
Open source operating systems like Linux, ClearOS, and OpenBSD include tons of
built-in networking and security features app thus making them more secure. You
have a list of choice: that range from tiny embedded systems for broadband wireless
routers, to giant enterprise Firewalls with all the bells-and-whistles. Thus here we
provides you with these Linux Firewall application for your open source Platform to
be used easily to make your network more secure to handle.
Top Open Source Firewall For Small Business

2. Open Source Firewalls: Endian Firewall
Consist with Multiple user functionality at same time. Endian Firewall offers a wide
range of product for the user. For other certain task such as Email, Web surfing,
VPN etc the range can exceed to more than 25 also. This firewall comes in a
compact, power-saving unit with four Gigabit Ethernet ports, two USB ports, 2GB
RAM, and 8GB storage.
For some features one can switch to the commercial Hardware too that consist of
management tools, support for commercial add-ons like Sophos anti-virus and
Commtouch anti-spam, virtual machine support, and various support options.

3. Open Source Firewalls: IPCop
Available free to download, IPCop is an open source Linux software which
you can easily install and use on your hardware. It consist of a well
managed Graphical UI interface. PCop doesn't try to pack in every bit of
networking functionality; rather then it sticks to firewall and Internet
gateway duties: packet filtering, proxy, traffic shaping, VPN and secure
remote access, user authentication, name services, and time server.
IPCop integrates with good network and system monitoring and
performance graphs that let you quickly see any trouble spots. It is free of
cost and comes with community support only.

4. Open Source Firewalls: OpenWRT
OpenWrt provides a fully writable filesystem with package management. This
frees you from the application selection and configuration provided by the
vendor and allows you to customize the device through the use of packages
to suit any application. For developer, OpenWrt is the framework to build an
application without having to build a complete firmware around it
The primary risk is a power interruption. If you can keep the lights on long
enough to flash the new firmware, you're set. Plus, a number of router
vendors install DD-WRT or OpenWRT rather than maintain their own
firmware

5. ClearOS Open source Firewall
The Open source firewall app allows administrators to simply
open ports (or port ranges) for services running locally on the
server. If a service requires connections from outside your
network to be made (i.e. running a web or mail service on a
system configured for gateway and server), a corresponding port
or port range will need to be added through this app.

6. Open Source Firewalls: Untangle Gateway
Untangle is one of the most famous Multi- function firewall that can
handle a wide range of function that comprises of user authentication
(including Active Directory integration) VPN, captive portal, Web filtering,
anti-virus, anti-spam, intrusion prevention, ad blocker, reporting, and
higher-end features such as WAN balancing and automatic failover. The
base package is free, and for further you can choose from a range of fee-
based add-ons