Traffic Shaping in pfSense: Part Five

Traffic shaping in pfSense

Configuring peer-to-peer networking settings in the pfSense traffic shaping wizard.

The next screen, “Peer-to-Peer Networking”, will let you set controls over many peer-to-peer (P2P) networking protocols. By design, P2P protocols will utilize all available bandwidth unless limits are put in place. If you expect P2P traffic on your network, it is a good practice to ensure that other traffic will not be degraded due to its use. To penalize P2P traffic in pfSense, first check the first check box at the top of the page.

Many P2P technologies will deliberately try to avoid detection. Bittorrent is especially guilty of this. It will often use non-standard or random ports, or even ports associated with other protocols. You can check the p2pCatchAll check box (the second check box on the page) which will cause any unrecognized traffic to be assumed as P2p traffic and its priority lowered accordingly. You can set hard bandwidth limits for this traffic in the edit box underneath the catch-all rule. The upload and download bandwidth limits can be set in percentages, or bits/kilobits/megabits/gigabits per second.

The remaining options consist of various known P2P protocols/applications. There are more than 20 in all. Check each one that you would like to be recognized. When you are done, press the Next button.

The next page covers network games settings. Many games rely on low latency to deliver a good online gaming experience. If someone tries to download large files or game patches while playing, then that traffic can easily swallow up the packets associated with the game itself and cause lags or disconnection. By checking the check box for prioritizing network gaming traffic (the first check box on the page), you can raise the priority of game traffic so that it will be transferred first and given a guaranteed chunk of bandwidth. There are many games listed here. Check all those which should be prioritized. Even if your game is not listed, you may still want to check a similar game (if there is one on the list) so that you will have a reference rule that you can alter later. When you are done configuring network gaming settings, press the Next button.

Traffic Shaping in pfSense: Part One

Traffic Shaping with pfSense

Using the traffic shaping wizard in pfSense 2.2.4.

Traffic shaping, otherwise known as network Quality of Service (QoS), is a means of prioritizing the network traffic crossing your firewall. Without traffic shaping, all packets are processed on a first in/first out basis by your firewall. QoS offers a means of prioritizing different types of traffic, ensuring that high priority services receive the bandwidth they need before lesser piroity services. The traffic shaper wizard in pfSense gives you the ability to quickly configure QoS for common scenarios, and custom rules may also be created for more complex tasks.

Traffic shaping is essentially like a gatekeeper in which important packets are prioritized, while regular packets have to wait, and low-priority packets are kept out until there is not enough higher-priority traffic to use up the bandwidth.

There are traffic shaping queues and traffic shaping rules. The queues are where bandwidth and priorities are actually allocated. Traffic shaping rules control how traffic is assigned into those queues. Rules for the shaper work in a similar way to firewall rules, and allow similar matching characteristics. If a packet matches a shaper rule, it will be assigned into the queues specified by that rule.

The idea of raising or lowering the priority of packets is a simple one, but one which has many possible applications. Here are a few ways in which traffic shaping can be used.

Traffic Shaping in pfSense: Prioritizing ACK Packets

Asymmetric Internet connections (where the download speed differs from the upload speed, usually in such a way that download speed > upload speed) are commonplace, especially with DSL. Some links are so out of balance that the maximum download speed is almost unattainable because it is difficult for the client to send back enough ACK packets to keep traffic flowing. ACK packets are transmitted back to the sender by the receiver to indicate that data has been successfully received, and to signal that it is OK to send more. If the sender does not receive ACKs in a timely manner, TCP’s congestion control will be invoked and it will slow down the connection.

This can happen if you are uploading and downloading simultaneously over an asymmetric connection. The uploading part of the circuit is full from the file upload, and there is little room to send ACK packets which allow downloads to keep flowing. By using the shaper to prioritize ACK packets, you can achieve faster, more stable download speeds on asymmetic links. [This is not as important on symmetric links, but it may still be desirable if the available outgoing bandwidth is heavily utilized.]

Traffic Shaping in pfSense: VoIP, Online Gaming and Peer-to-Peer Traffic

If your VoIP calls use the same circuit as data, then uploads and downloads may degrade your call quality. pfSense can prioritize the call traffic above other protocols and ensure that the calls make it through clearly without breaking up. If there are other transfers occurring simultaneously when the VoIP call is in progress, the speed of the other transfers will be reduced to leave room for the calls.

There are also options in pfSense to give priority to the traffic associated with network gaming. Similar to prioritizing VoIP calls, the effect is that even if you are downloading while playing, the response time of the game should be nearly as fast as if the rest of your connection were idle.

In addition, by lowering the priority of traffic associated with known peer-to-peer ports, you will have the assurance that even if these programs are in use, they won’t hinder other traffic on your network. Due to peer-to-peer traffic’s lower priority, other protocols will be favored over P2P traffic, which will be limited when any other services need the bandwidth.

In the next article, we will discuss some of the limitations of pfSense’s traffic shaper.

External Links:

Traffic Shaping at Wikipedia

pfSense Traffic Shaping: Part One

pfSense Traffic Shaping

The traffic shaping wizard page in the pfSense web GUI.

Traffic shaping (also known as “packet shaping”, or “Quality of Service” [QoS]) is a computer network traffic management technique which prioritizes some datagrams while delaying other datagrams to bring them into compliance with a desired traffic profile. It is a form of rate limiting (a method of controlling traffic by which traffic that exceeds a specified rate is dropped or delayed) and is used to optimize or guarantee performance, improve latency, and/or increase usable bandwidth for some kinds of packets by delaying other kinds. It is widely used for network traffic engineering, and often appears in ISPs’ networks as one of several Internet Traffic Management Practices (ITMPs).

pfSense Traffic Shaping: An Example

pfSense Traffic Shaping

Configuring VoIP settings in the pfSense traffic shaping wizard.

In the following example, we will use pfSense traffic shaping to limit VoIP throughput to 125 kbps. First, navigate to Firewall -> Traffic Shaper. Select the “Wizards” tab. From the Wizards table, click on “Single WAN multi LAN“. [Assume we have a LAN and a DMZ.] On the next page, at “Enter number of LAN type connections“, enter “2”. At “Link Upload“, type the upload bandwidth (remembering to select either Kbit/s, Mbit/s, or Gbit/s in the drop-down boxes), and at “Link Download“, type the download bandwidth. Leave the other settings unchanged and click the “Next” button.

The next page deals with VoIP settings. At “Enable“, click on the check box to prioritize VOIP traffic. Under “VOIP specific settings“, assume we’re using Asterisk for VoIP and at “Provider” select “Asterisk/Vonage“. Set “Upload Speed” to 125 Kilobit/s, and set “Download Speed” to 125 Kilobit/s. Leave the other settings unchanged and click the “Next” button.

The next page, “PenaltyBox“, allows us to reduce the priority of an IP address or alias. We will assume that we have no use for this feature right now and click on the “Next” button.

pfSense Traffic Shaping

The final page in the pfSense traffic shaping wizard

The next page is for peer-to-peer networking and allows you to lower the priority and/or disable about 20 different specific P2P protocols. There is also a “P2P Catch all” queue which allows us to place all uncategorized traffic into the P2P queue. Again, we will assume that we have no use for this feature now and click on the “Next” button.

The next page is for network games, and allows us to raise the priority of gaming traffic and/or enable/disable specific games (e.g. Call of Duty, Unreal Tournament, World of Warcraft, and several others). Again we will click the “Next” button.

The final page, “Other Applications“, allows us to shape other common types of traffic. These include remote access programs like PC Anywhere, messaging programs like IRC and Teamspeak, VPN traffic, and other programs. Click on the “Next” button. On the next page, click the “Finish” button to apply the new settings.

We now have used pfSense traffic shaping to prioritize VoIP traffic while also limiting the amount of VoIP throughput to 125 Kbit/s. In part two of this series on traffic shaping, I will cover the Hierarchical Fair Service Curve, one of several traffic shaping algorithms supported by pfSense. In part three, I will cover class based queuing and priority queuing.

External Links:

Traffic Shaping Guide at (with links)

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