Traffic shaping in Linux

• All interface must have two scheduler for incoming / out going traffic
• Scheduler is called qdisc in the tc command.
• root qdisc = egress = out going scheduler
• ingress qdisc = in coming scheduler
• the default qdisc is pfifo_fast, which is a classless qdisc
• htb is a classful qdisc, you should create a class hierarchy (invert tree) to use it.
• for classful qdisc like htb, you should attach filters to divert packets to nodes in the invert tree.

Read this: http://linux-ip.net/articles/Traffic-Control-HOWTO/index.html

Or this: http://tldp.org/HOWTO/Traffic-Control-HOWTO/index.html

#!/bin/bash

# Set the following values to somewhat less than your actual download
# and uplink speed. In kilobits
DOWNLINK=80000
UPLINK=30000
DEV=eth0

# clean existing down- and uplink qdiscs, hide errors
tc qdisc del dev $DEV root    2> /dev/null > /dev/null
tc qdisc del dev $DEV ingress 2> /dev/null > /dev/null

###### uplink

# install root HTB, point default traffic to 1:20:
tc qdisc add dev $DEV root handle 1: htb default 20

# start creating the class hierarchy (invert tree):
# First of all, the root the the class.
# It shape everything at $UPLINK speed - this prevents huge queues in your
# DSL modem which destroy latency:
tc class add dev $DEV parent 1: classid 1:1 htb rate ${UPLINK}kbit
# \ burst 6k

# high prio class 1:10:
tc class add dev $DEV parent 1:1 classid 1:10 htb rate ${UPLINK}kbit prio 1
# \ burst 6k prio 1

# bulk & default class 1:20 - gets slightly less traffic, 
# and a lower priority:
tc class add dev $DEV parent 1:1 classid 1:20 htb rate $((9*${UPLINK}/10))kbit prio 2 
# \ burst 6k prio 2

# for netem module, use it to test protocol stack
tc class add dev $DEV parent 1:1 classid 1:30 htb rate $((9*${UPLINK}/10))kbit prio 2 

# both get Stochastic Fairness:
echo "# both get Stochastic Fairness:"
tc qdisc add dev $DEV parent 1:10 handle 10: sfq perturb 10
tc qdisc add dev $DEV parent 1:20 handle 20: sfq perturb 10

# attach netem to 1:30
tc qdisc add dev $DEV parent 1:30 handle 30: netem delay 300ms 30ms distribution normal loss 20% 25%

# example to use the netem module:
# web server traffic go to netem at 1:30 
#tc filter add dev $DEV parent 1:0 protocol ip prio 10 u32 \
#  match ip sport 80 0xffff flowid 1:30
  
# TOS Minimum Delay (ssh, NOT scp) in 1:10:
tc filter add dev $DEV parent 1:0 protocol ip prio 10 u32 \
  match ip tos 0x10 0xff  flowid 1:10

# ICMP (ip protocol 1) in the interactive class 1:10 so we 
# can do measurements & impress our friends:
tc filter add dev $DEV parent 1:0 protocol ip prio 10 u32 \
	match ip protocol 1 0xff flowid 1:10

# To speed up downloads while an upload is going on, put ACK packets in
# the interactive class:
tc filter add dev $DEV parent 1:0 protocol ip prio 10 u32 \
   match ip protocol 6 0xff \
   match u8 0x05 0x0f at 0 \
   match u16 0x0000 0xffc0 at 2 \
   match u8 0x10 0xff at 33 \
   flowid 1:10

# rest is 'non-interactive' ie 'bulk' and ends up in 1:20

########## downlink #############
# slow downloads down to somewhat less than the real speed  to prevent 
# queuing at our ISP. Tune to see how high you can set it.
# ISPs tend to have *huge* queues to make sure big downloads are fast
#
# attach ingress policer:

tc qdisc add dev $DEV handle ffff: ingress

# filter *everything* to it (0.0.0.0/0), drop everything that's
# coming in too fast:

tc filter add dev $DEV parent ffff: protocol ip prio 50 u32 match ip src \
   0.0.0.0/0 police rate ${DOWNLINK}kbit burst 10k drop flowid :1

### End of script ###