Title: Fair Internet bandwidth management on a network using Linux

	Title: Fair Internet bandwidth management on a network using Linux
	Author: Solène
	Date: 05 August 2022
	Tags: linux bandwidth qos
	Description: This article introduce you to network quality of service
	to make a router fairly assigning bandwidth to network consumers on
	your LAN.

	# Introduction

	A while ago I wrote an OpenBSD guide to fairly share the Internet
	bandwidth to the LAN network, it was more or less working. Now I
	switched my router to Linux, I wanted to achieve the same.
	Unfortunately, it's not really documented as well as on OpenBSD.

	The command needed for this job is "tc", acronym for Traffic Control,
	the Jack of all trades when it comes to manipulate your network
	traffic. It can add delays or packets lost (this is fun when you want
	to simulate poor conditions), but also traffic shaping and Quality of
	Service (QoS).

	Wikipedia page about tc

	Fortunately, tc is not that complicated for what we will achieve in
	this how-to (fair share) and will give results way better than what I
	achieved with OpenBSD!

	# How it works

	I don't want to explain how the whole stack involved works, but with tc
	we will define a queue on the interface we want to apply the QoS, it
	will create a number of flows assigned to each active network streams,
	each active flow will receive 1/total_active_flows shares of bandwidth.
	It mean if you have three connections downloading data (from the same
	computer or three different computers), they should in theory receive
	1/3 of bandwidth each. In practice, you don't get exactly that, but
	it's quite close.

	# Setup

	I made a script with variables to make it easy to reuse, it deletes any
	traffic control set on the interfaces and then creates the
	configuration. You are supposed to run it at boot.

	It contains two variables, DOWNLOAD_LIMIT and UPLOAD_LIMIT that should
	be approximately 95% of each maximum speed, it can be defined in bits
	with kbits/mbits or in bytes with kbps/mbps, the reason to use 95% is
	to let the router some room for organizing the packets. It's like a
	"15 puzzle", you need one empty square to use it.

	```sh
	#!/bin/sh

	TC=$(which tc)

	# LAN interface on which you have NAT
	LAN_IF=br0

	# WAN interface which connects to the Internet
	WAN_IF=eth0

	# 95% of maximum download
	DOWNLOAD_LIMIT=13110kbit

	# 95% of maximum upload
	UPLOAD_LIMIT=840kbit

	$TC qdisc del dev $LAN_IF root
	$TC qdisc del dev $WAN_IF root

	$TC qdisc add dev $WAN_IF root handle 1: htb default 1
	$TC class add dev $WAN_IF parent 1: classid 1:1 htb rate $UPLOAD_LIMIT
	$TC qdisc add dev $WAN_IF parent 1:1 fq_codel noecn

	$TC qdisc add dev $LAN_IF root handle 1: htb default 1
	$TC class add dev $LAN_IF parent 1: classid 1:1 htb rate $DOWNLOAD_LIMIT
	$TC qdisc add dev $LAN_IF parent 1:1 fq_codel
	```

	# Conclusion

	tc is very effective but not really straightfoward to understand.
	What's cool is you can apply it on the fly without incidence.

	It has been really effective for me, now if some device is downloading
	on the network, it doesn't affect much the other devices when they need
	to reach the Internet.

	# Credits

	After lurking on the Internet looking for documentation about tc, I
	finally found someone who made a clear explanation about this tool. tc
	is documented, but it's too abstract for me.

	linux home router traffic shaping with fq_codel