pfSense – Firewall and Router OS

pfSense Used as a firewall and router os, the project started in 2004 forked from the m0n0wall project but focused on full PC installations. pfSense also offers an embedded image for Compact Flash based installations.

Features :


  • Filtering by source and destination IP, IP protocol, source and destination port for TCP and UDP traffic
  • Able to limit simultaneous connections on a per-rule basis
  • pfSense utilizes p0f, an advanced passive OS/network fingerprinting utility to allow you to filter by the Operating System initiating the connection. Want to allow FreeBSD and Linux machines to the Internet, but block Windows machines? pfSense can do so (amongst many other possibilities) by passively detecting the Operating System in use.
  • Option to log or not log traffic matching each rule.
  • Highly flexible policy routing possible by selecting gateway on a per-rule basis (for load balancing, failover, multiple WAN, etc.)
  • Aliases allow grouping and naming of IPs, networks and ports. This helps keep your firewall ruleset clean and easy to understand, especially in environments with multiple public IPs and numerous servers.
  • Transparent layer 2 firewalling capable – can bridge interfaces and filter traffic between them, even allowing for an IP-less firewall (though you probably want an IP for management purposes).
  • Packet normalization – Description from the pf scrub documentation – “‘Scrubbing’ is the normalization of packets so there are no ambiguities in interpretation by the ultimate destination of the packet. The scrub directive also reassembles fragmented packets, protecting some operating systems from some forms of attack, and drops TCP packets that have invalid flag combinations.”
    • Enabled in pfSense by default
    • Can disable if necessary. This option causes problems for some NFS implementations, but is safe and should be left enabled on most installations.
  • Disable filter – you can turn off the firewall filter entirely if you wish to turn pfSense into a pure router.

State Table

The firewall’s state table maintains information on your open network connections. pfSense is a stateful firewall, by default all rules are stateful.

Most firewalls lack the ability to finely control your state table. pfSense has numerous features allowing granular control of your state table, thanks to the abilities of OpenBSD’s pf.

  • Adjustable state table size – there are multiple production pfSense installations using several hundred thousand states. The default state table size is 10,000, but it can be increased on the fly to your desired size. Each state takes approximately 1 KB of RAM, so keep in mind memory usage when sizing your state table. Do not set it arbitrarily high.
  • On a per-rule basis:
    • Limit simultaneous client connections
    • Limit states per host
    • Limit new connections per second
    • Define state timeout
    • Define state type
  • State types – pfSense offers multiple options for state handling.
    • Keep state – Works with all protocols. Default for all rules.
    • Modulate state – Works only with TCP. pfSense will generate strong Initial Sequence Numbers (ISNs) on behalf of the host.
    • Synproxy state – Proxies incoming TCP connections to help protect servers from spoofed TCP SYN floods. This option includes the functionality of keep state and modulate state combined.
    • None – Do not keep any state entries for this traffic. This is very rarely desirable, but is available because it can be useful under some limited circumstances.
  • State table optimization options – pf offers four options for state table optimization.
    • Normal – the default algorithm
    • High latency – Useful for high latency links, such as satellite connections. Expires idle connections later than normal.
    • Aggressive – Expires idle connections more quickly. More efficient use of hardware resources, but can drop legitimate connections.
    • Conservative – Tries to avoid dropping legitimate connections at the expense of increased memory usage and CPU utilization.

Network Address Translation (NAT)

  • Port forwards including ranges and the use of multiple public IPs
  • 1:1 NAT for individual IPs or entire subnets.
  • Outbound NAT
    • Default settings NAT all outbound traffic to the WAN IP. In multiple WAN scenarios, the default settings NAT outbound traffic to the IP of the WAN interface being used.
    • Advanced Outbound NAT allows this default behavior to be disabled, and enables the creation of very flexible NAT (or no NAT) rules.
  • NAT Reflection – in some configurations, NAT reflection is possible so services can be accessed by public IP from internal networks.

NAT Limitations

  • PPTP and GRE Limitation – The state tracking code in pf for the GRE protocol can only track a single session per public IP per external server. This means if you use PPTP VPN connections, only one internal machine can connect simultaneously to a PPTP server on the Internet. A thousand machines can connect simultaneously to a thousand different PPTP servers, but only one simultaneously to a single server. The only available work around is to use multiple public IPs on your firewall, one per client, or to use multiple public IPs on the external PPTP server. This is not a problem with other types of VPN connections. A solution for this is currently under development.
  • SIP Limitation – By default, all TCP and UDP traffic other than SIP and IPsec gets the source port rewritten. More information on this can be found in the static port documentation. Because this source port rewriting is how pf tracks which internal IP made the connection to the given external server, and most all SIP traffic uses the same source port, only one SIP device can connect simultaneously to a single server on the Internet. Unless your SIP devices can operate with source port rewriting (most can’t), you cannot use multiple phones with a single outside server without using a dedicated public IP per device. The sipproxd package now provides a solution for this problem in pfSense 1.2.1 and newer.
  • NAT Reflection limitations – NAT reflection can only be used with port ranges less than 500 ports and cannot be used with 1:1 NAT hosts.


CARP from OpenBSD allows for hardware failover. Two or more firewalls can be configured as a failover group. If one interface fails on the primary or the primary goes offline entirely, the secondary becomes active. pfSense also includes configuration synchronization capabilities, so you make your configuration changes on the primary and they automatically synchronize to the secondary firewall.

pfsync ensures the firewall’s state table is replicated to all failover configured firewalls. This means your existing connections will be maintained in the case of failure, which is important to prevent network disruptions.


  • Only works with static public IPs, does not work with DHCP, PPPoE, PPTP, or BigPond type WANs (will be resolved in a future release)
  • Requires a minimum of three public IP addresses (will be resolved in a future release)
  • Backup firewalls are idle (active-passive failover), no active-active clustering is possible at this time.
  • Failover is not instantaneous, it takes about 5 seconds to switch a backup host to master. During this time no traffic will be passed, but existing states will maintain connectivity after failover is completed. This 5 second outage during a failure isn’t even noticeable in most environments.

Load Balancing

Outbound Load Balancing

Outbound load balancing is used with multiple WAN connections to provide load balancing and failover capabilities. Traffic is directed to the desired gateway or load balancing pool on a per-firewall rule basis.

Inbound Load Balancing

Inbound load balancing is used to distribute load between multiple servers. This is commonly used with web servers, mail servers, and others. Servers that fail to respond to ping requests or TCP port connections are removed from the pool.

  • Equally distributes load between all available servers – unable to unequally distribute load between servers at this time.
  • Only checks if the server responds to pings or TCP port connections. Cannot check if the server is returning valid content.


pfSense offers three options for VPN connectivity, IPsec, OpenVPN, and PPTP.


IPsec allows connectivity with any device supporting standard IPsec. This is most commonly used for site to site connectivity to other pfSense installations, other open source firewalls (m0n0wall, etc.), and most all commercial firewall solutions (Cisco, Juniper, etc.). It can also be used for mobile client connectivity.

  • NAT-T is not supported, which means mobile clients behind NAT are not supported. This limits pfSense’s usefulness with mobile IPsec clients. OpenVPN or PPTP is a better solution.
  • Only one end of an IPsec tunnel can have a dynamic IP address.
  • Some of the more advanced capabilities of ipsec-tools are not yet supported, including DPD, XAuth, NAT-T, and others.


OpenVPN is a flexible, powerful SSL VPN solution supporting a wide range of client operating systems. See the OpenVPN website for details on its abilities.

  • Not all of the capabilities of OpenVPN are supported yet. Support for virtually all of OpenVPN’s capabilities will be included in the next release.
  • Filtering of OpenVPN traffic is not yet possible. Support for this is in 2.0.

PPTP Server

PPTP is a popular VPN option because nearly every OS has a built in PPTP client, including every Windows release since Windows 95 OSR2. See this Wikipedia article for more information on the PPTP protocol.

The pfSense PPTP Server can use a local user database, or a RADIUS server for authentication. RADIUS accounting is also supported. Firewall rules on the PPTP interface control traffic initiated by PPTP clients.

  • Because of limitations in pf NAT, when the PPTP Server is enabled, PPTP clients cannot use the same public IP for outbound PPTP connections. This means if you have only one public IP, and use the PPTP Server, PPTP clients inside your network will not work. The work around is to use a second public IP with Advanced Outbound NAT for your internal clients. See also the PPTP limitation under NAT on this page.

PPPoE Server

pfSense offers a PPPoE server. For more information on the PPPoE protocol, see this Wikipedia entry. A local user database can be used for authentication, and RADIUS authentication with optional accounting is also supported.

Reporting and Monitoring

RRD Graphs

The RRD graphs in pfSense maintain historical information on the following.

  • CPU utilization
  • Total throughput
  • Firewall states
  • Individual throughput for all interfaces
  • Packets per second rates for all interfaces
  • WAN interface gateway(s) ping response times
  • Traffic shaper queues on systems with traffic shaping enable

Real Time Information

Historical information is important, but sometimes it’s more important to see real time information.

SVG graphs are available that show real time throughput for each interface.

For traffic shaper users, the Status -> Queues screen provides a real time display of queue usage using AJAX updated gauges.

The front page includes AJAX gauges for display of real time CPU, memory, swap and disk usage, and state table size.

Dynamic DNS

A Dynamic DNS client is included to allow you to register your public IP with a number of dynamic DNS service providers.

  • DynDNS
  • DHS
  • DyNS
  • easyDNS
  • No-IP
  • ZoneEdit

A client is also available for RFC 2136 dynamic DNS updates, for use with DNS servers like BIND which support this means of updating.


  • Only works on primary WAN interface – multi-WAN support is available in 2.0.
  • Can only update one account with a single provider. 2.0 enables the use of unlimited accounts.
  • Only works when pfSense has the public IP assigned to one of its interfaces. If you have a modem that obtains your public IP and gives pfSense a private IP, the private IP will be registered with the provider. In 2.0, there is an option to determine your actual public IP and correctly register it.

Captive Portal

Captive portal allows you to force authentication, or redirection to a click through page for network access. This is commonly used on hot spot networks, but is also widely used in corporate networks for an additional layer of security on wireless or Internet access. For more information on captive portal technology in general, see the Wikipedia article on the topic. The following is a list of features in the pfSense Captive Portal.

  • Maximum concurrent connections – Limit the number of connections to the portal itself per client IP. This feature prevents a denial of service from client PCs sending network traffic repeatedly without authenticating or clicking through the splash page.
  • Idle timeout – Disconnect clients who are idle for more than the defined number of minutes.
  • Hard timeout – Force a disconnect of all clients after the defined number of minutes.
  • Logon pop up window – Option to pop up a window with a log off button.
  • URL Redirection – after authenticating or clicking through the captive portal, users can be forcefully redirected to the defined URL.
  • MAC filtering – by default, pfSense filters using MAC addresses. If you have a subnet behind a router on a captive portal enabled interface, every machine behind the router will be authorized after one user is authorized. MAC filtering can be disabled for these scenarios.
  • Authentication options – There are three authentication options available.
    • No authentication – This means the user just clicks through your portal page without entering credentials.
    • Local user manager – A local user database can be configured and used for authentication.
    • RADIUS authentication – This is the preferred authentication method for corporate environments and ISPs. It can be used to authenticate from Microsoft Active Directory and numerous other RADIUS servers.
  • RADIUS capabilities
    • Forced re-authentication
    • Able to send Accounting updates
    • RADIUS MAC authentication allows captive portal to authenticate to a RADIUS server using the client’s MAC address as the user name and password.
    • Allows configuration of redundant RADIUS servers.
  • HTTP or HTTPS – The portal page can be configured to use either HTTP or HTTPS.
  • Pass-through MAC and IP addresses – MAC and IP addresses can be white listed to bypass the portal. Any machines with NAT port forwards will need to be bypassed so the reply traffic does not hit the portal. You may wish to exclude some machines for other reasons.
  • File Manager – This allows you to upload images for use in your portal pages.


  • Can only run on one interface simultaneously.
  • “Reverse” portal, i.e. capturing traffic originating from the Internet and entering your network, is not possible.
  • Only entire IP and MAC addresses can be excluded from the portal, not individual protocols and ports.
  • Currently not compatible with multi-WAN rules. We hope this will be resolved in 2.0.

DHCP Server and Relay

pfSense includes both DHCP Server and Relay functionality

pfSense Official website :

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