?

Log in

No account? Create an account

Traffic Shaping

« previous entry | next entry »
Oct. 7th, 2005 | 10:41 pm

After being annoyed by the latency on my ssh connection while I was bittorrenting some dj mixed music, I went off and grabed a traffic shaping script for my little wrt54g router.

I installed kmod-sched, kmod-iptables-extra, and tc to get the right kernel modules and the traffic shaper program. As the script I hacked was designed for a full box instead of the limited openwrt I needed to also added the following to my /etc/services file.

ssh     22/tcp
telnet  23/tcp
http    80/tcp

I made a few modifications to the shaper script to deal with the fact OpenWrt is using ash instead of bash, and the imq module doesn't seem to exist. Also after some brief efforts I didn't get the iptables length filter to match.

On the plus side after running the script my ssh connection started behaving much better, even though bittorrent is uploading at near my max throughput. The odd thing is when I turn the script off ssh still behaves... Odd. It works, I need sleep, not going to worry about it right now.

#!/bin/sh
#
# myshaper - DSL/Cable modem outbound traffic shaper and prioritizer.
#            Based on the ADSL/Cable wondershaper (www.lartc.org)
#
# Written by Dan Singletary (8/7/02)
# Modified by Diane Trout (6 Oct 2005)
#
# NOTE!! - This script assumes your kernel has been patched with the
#          appropriate HTB queue and IMQ patches available here:
#          (subnote: future kernels may not require patching)
#
#       http://luxik.cdi.cz/~devik/qos/htb/
#       http://luxik.cdi.cz/~patrick/imq/
#
# Configuration options for myshaper:
#  DEV    - set to ethX that connects to DSL/Cable Modem
#  RATEUP - set this to slightly lower than your
#           outbound bandwidth on the DSL/Cable Modem.
#           I have a 1500/128 DSL line and setting
#           RATEUP=90 works well for my 128kbps upstream.
#           However, your mileage may vary.
#  RATEDN - set this to slightly lower than your
#           inbound bandwidth on the DSL/Cable Modem.
#
#
#  Theory on using imq to "shape" inbound traffic:
#
#     It's impossible to directly limit the rate of data that will
#  be sent to you by other hosts on the internet.  In order to shape
#  the inbound traffic rate, we have to rely on the congestion avoidance
#  algorithms in TCP.  Because of this, WE CAN ONLY ATTEMPT TO SHAPE
#  INBOUND TRAFFIC ON TCP CONNECTIONS.  This means that any traffic that
#  is not tcp should be placed in the high-prio class, since dropping
#  a non-tcp packet will most likely result in a retransmit which will
#  do nothing but unnecessarily consume bandwidth.  
#     We attempt to shape inbound TCP traffic by dropping tcp packets
#  when they overflow the HTB queue which will only pass them on at
#  a certain rate (RATEDN) which is slightly lower than the actual
#  capability of the inbound device.  By dropping TCP packets that
#  are over-rate, we are simulating the same packets getting dropped
#  due to a queue-overflow on our ISP's side.  The advantage of this
#  is that our ISP's queue will never fill because TCP will slow it's
#  transmission rate in response to the dropped packets in the assumption
#  that it has filled the ISP's queue, when in reality it has not.
#     The advantage of using a priority-based queuing discipline is
#  that we can specifically choose NOT to drop certain types of packets
#  that we place in the higher priority buckets (ssh, telnet, etc).  This
#  is because packets will always be dequeued from the lowest priority class
#  with the stipulation that packets will still be dequeued from every
#  class fairly at a minimum rate (in this script, each bucket will deliver
#  at least it's fair share of 1/7 of the bandwidth).  
#
#  Reiterating main points:
#   * Dropping a tcp packet on a connection will lead to a slower rate
#     of reception for that connection due to the congestion avoidance algorithm.
#   * We gain nothing from dropping non-TCP packets.  In fact, if they
#     were important they would probably be retransmitted anyways so we want to
#     try to never drop these packets.  This means that saturated TCP connections
#     will not negatively effect protocols that don't have a built-in retransmit like TCP.
#   * Slowing down incoming TCP connections such that the total inbound rate is less
#     than the true capability of the device (ADSL/Cable Modem) SHOULD result in little
#     to no packets being queued on the ISP's side (DSLAM, cable concentrator, etc).  Since
#     these ISP queues have been observed to queue 4 seconds of data at 1500Kbps or 6 megabits
#     of data, having no packets queued there will mean lower latency.
#
#  Caveats (questions posed before testing):
#   * Will limiting inbound traffic in this fashion result in poor bulk TCP performance?
#     - Preliminary answer is no!  Seems that by prioritizing ACK packets (small <64b)
#       we maximize throughput by not wasting bandwidth on retransmitted packets
#       that we already have.
#   

# NOTE: The following configuration works well for my 
# setup: 3.0M/256K Charter Cable Modem (untuned currently)

DEV=$(nvram get wan_ifname)
RATEUP=240
RATEUPSLICE=$(expr $RATEUP / 7 )
# not so important since I currently have downstream shaping off
RATEDN=2500  # Note that this is significantly lower than the capacity of 1500.
             # Because of this, you may not want to bother limiting inbound traffic
             # until a better implementation such as TCP window manipulation can be used.
RATEDNSLICE=$(expr $RATEDN / 2 )

# 
# End Configuration Options
#
if [ "$1" = "status" ]
then
        echo "[qdisc]"
        tc -s qdisc show dev $DEV
#        tc -s qdisc show dev imq0
        echo "[class]"
        tc -s class show dev $DEV
#        tc -s class show dev imq0
        echo "[filter]"
        tc -s filter show dev $DEV
#        tc -s filter show dev imq0
        echo "[iptables]"
        iptables -t mangle -L MYSHAPER-OUT -v -x 2> /dev/null
        iptables -t mangle -L MYSHAPER-IN -v -x 2> /dev/null
        exit
fi

# Reset everything to a known state (cleared)
tc qdisc del dev $DEV root    2> /dev/null > /dev/null
#tc qdisc del dev imq0 root 2> /dev/null > /dev/null
iptables -t mangle -D POSTROUTING -o $DEV -j MYSHAPER-OUT 2> /dev/null > /dev/null
iptables -t mangle -F MYSHAPER-OUT 2> /dev/null > /dev/null
iptables -t mangle -X MYSHAPER-OUT 2> /dev/null > /dev/null
iptables -t mangle -D PREROUTING -i $DEV -j MYSHAPER-IN 2> /dev/null > /dev/null
iptables -t mangle -F MYSHAPER-IN 2> /dev/null > /dev/null
iptables -t mangle -X MYSHAPER-IN 2> /dev/null > /dev/null
#ip link set imq0 down 2> /dev/null > /dev/null
#rmmod imq 2> /dev/null > /dev/null
rmmod sch_sfq 2> /dev/null > /dev/null
rmmod sch_htb 2> /dev/null > /dev/null
rmmod cls_fw 2> /dev/null > /dev/null
rmmod ipt_length 2> /dev/null > /dev/null
rmmod ip6t_length 2> /dev/null > /dev/null

if [ "$1" = "stop" ] 
then 
        echo "Shaping removed on $DEV."
        exit
fi

###########################################################
#
# Outbound Shaping (limits total bandwidth to RATEUP)

insmod /lib/modules/$(uname -r)/sch_htb.o
insmod /lib/modules/$(uname -r)/sch_sfq.o
insmod /lib/modules/$(uname -r)/cls_fw.o
insmod /lib/modules/$(uname -r)/ipt_length.o
#insmod /lib/modules/$(uname -r)/ip6t_length.o

# set queue size to give latency of about 2 seconds on low-prio packets
ip link set dev $DEV qlen 30

# changes mtu on the outbound device.  Lowering the mtu will result
# in lower latency but will also cause slightly lower throughput due 
# to IP and TCP protocol overhead.
ip link set dev $DEV mtu 1000

# add HTB root qdisc
tc qdisc add dev $DEV root handle 1: htb default 26

# add main rate limit classes
tc class add dev $DEV parent 1: classid 1:1 htb rate ${RATEUP}kbit

# add leaf classes - We grant each class at LEAST it's "fair share" of bandwidth.
#                    this way no class will ever be starved by another class.  Each
#                    class is also permitted to consume all of the available bandwidth
#                    if no other classes are in use.
tc class add dev $DEV parent 1:1 classid 1:20 htb rate ${RATEUPSLICE}kbit ceil ${RATEUP}kbit prio 0
tc class add dev $DEV parent 1:1 classid 1:21 htb rate ${RATEUPSLICE}kbit ceil ${RATEUP}kbit prio 1
tc class add dev $DEV parent 1:1 classid 1:22 htb rate ${RATEUPSLICE}kbit ceil ${RATEUP}kbit prio 2
tc class add dev $DEV parent 1:1 classid 1:23 htb rate ${RATEUPSLICE}kbit ceil ${RATEUP}kbit prio 3
tc class add dev $DEV parent 1:1 classid 1:24 htb rate ${RATEUPSLICE}kbit ceil ${RATEUP}kbit prio 4
tc class add dev $DEV parent 1:1 classid 1:25 htb rate ${RATEUPSLICE}kbit ceil ${RATEUP}kbit prio 5
tc class add dev $DEV parent 1:1 classid 1:26 htb rate ${RATEUPSLICE}kbit ceil ${RATEUP}kbit prio 6

# attach qdisc to leaf classes - here we at SFQ to each priority class.  SFQ insures that
#                                within each class connections will be treated (almost) fairly.
tc qdisc add dev $DEV parent 1:20 handle 20: sfq perturb 10
tc qdisc add dev $DEV parent 1:21 handle 21: sfq perturb 10
tc qdisc add dev $DEV parent 1:22 handle 22: sfq perturb 10
tc qdisc add dev $DEV parent 1:23 handle 23: sfq perturb 10
tc qdisc add dev $DEV parent 1:24 handle 24: sfq perturb 10
tc qdisc add dev $DEV parent 1:25 handle 25: sfq perturb 10
tc qdisc add dev $DEV parent 1:26 handle 26: sfq perturb 10

# filter traffic into classes by fwmark - here we direct traffic into priority class according to
#                                         the fwmark set on the packet (we set fwmark with iptables
#                                         later).  Note that above we've set the default priority
#                                         class to 1:26 so unmarked packets (or packets marked with
#                                         unfamiliar IDs) will be defaulted to the lowest priority
#                                         class.
tc filter add dev $DEV parent 1:0 prio 0 protocol ip handle 20 fw flowid 1:20
tc filter add dev $DEV parent 1:0 prio 0 protocol ip handle 21 fw flowid 1:21
tc filter add dev $DEV parent 1:0 prio 0 protocol ip handle 22 fw flowid 1:22
tc filter add dev $DEV parent 1:0 prio 0 protocol ip handle 23 fw flowid 1:23
tc filter add dev $DEV parent 1:0 prio 0 protocol ip handle 24 fw flowid 1:24
tc filter add dev $DEV parent 1:0 prio 0 protocol ip handle 25 fw flowid 1:25
tc filter add dev $DEV parent 1:0 prio 0 protocol ip handle 26 fw flowid 1:26

# add MYSHAPER-OUT chain to the mangle table in iptables - this sets up the table we'll use
#                                                      to filter and mark packets.
iptables -t mangle -N MYSHAPER-OUT
iptables -t mangle -I POSTROUTING -o $DEV -j MYSHAPER-OUT

# add fwmark entries to classify different types of traffic - Set fwmark from 20-26 according to
#                                                             desired class. 20 is highest prio.
iptables -t mangle -A MYSHAPER-OUT -p tcp --sport 0:1024 -j MARK --set-mark 23 # Default for low port traffic 
iptables -t mangle -A MYSHAPER-OUT -p tcp --dport 0:1024 -j MARK --set-mark 23 # "" 
iptables -t mangle -A MYSHAPER-OUT -p tcp --dport 20 -j MARK --set-mark 26     # ftp-data port, low prio
iptables -t mangle -A MYSHAPER-OUT -p tcp --dport 5190 -j MARK --set-mark 23   # aol instant messenger
iptables -t mangle -A MYSHAPER-OUT -p icmp -j MARK --set-mark 20               # ICMP (ping) - high prio, impress friends
iptables -t mangle -A MYSHAPER-OUT -p udp -j MARK --set-mark 21                # DNS name resolution (small packets)
iptables -t mangle -A MYSHAPER-OUT -p tcp --dport ssh -j MARK --set-mark 22    # secure shell
iptables -t mangle -A MYSHAPER-OUT -p tcp --sport ssh -j MARK --set-mark 22    # secure shell
iptables -t mangle -A MYSHAPER-OUT -p tcp --dport telnet -j MARK --set-mark 22 # telnet (ew...)
iptables -t mangle -A MYSHAPER-OUT -p tcp --sport telnet -j MARK --set-mark 22 # telnet (ew...)
#iptables -t mangle -A MYSHAPER-OUT -p ipv6-crypt -j MARK --set-mark 24         # IPSec - we don't know what the payload is though...
iptables -t mangle -A MYSHAPER-OUT -p tcp --sport http -j MARK --set-mark 25   # Local web server
# FIXME: I don't know why this isn't working, I'm loading the ipt_length module
#iptables -t mangle -A MYSHAPER-OUT -p tcp -m length --length :64 -j MARK --set-mark 21 # small packets (probably just ACKs)
iptables -t mangle -A MYSHAPER-OUT -m mark --mark 0 -j MARK --set-mark 26      # redundant- mark any unmarked packets as 26 (low prio)

# Done with outbound shaping
#
####################################################

echo "Outbound shaping added to $DEV.  Rate: ${RATEUP}Kbit/sec."

# uncomment following line if you only want upstream shaping.
exit

####################################################
#
# Inbound Shaping (limits total bandwidth to RATEDN)

# make sure imq module is loaded

insmod imq numdevs=1

ip link set imq0 up

# add qdisc - default low-prio class 1:21

tc qdisc add dev imq0 handle 1: root htb default 21

# add main rate limit classes
tc class add dev imq0 parent 1: classid 1:1 htb rate ${RATEDN}kbit

# add leaf classes - TCP traffic in 21, non TCP traffic in 20
#
tc class add dev imq0 parent 1:1 classid 1:20 htb rate ${RATEDNSLICE}kbit ceil ${RATEDN}kbit prio 0
tc class add dev imq0 parent 1:1 classid 1:21 htb rate ${RATEDNSLICE}kbit ceil ${RATEDN}kbit prio 1

# attach qdisc to leaf classes - here we at SFQ to each priority class.  SFQ insures that
#                                within each class connections will be treated (almost) fairly.
tc qdisc add dev imq0 parent 1:20 handle 20: sfq perturb 10
tc qdisc add dev imq0 parent 1:21 handle 21: red limit 1000000 min 5000 max 100000 avpkt 1000 burst 50

# filter traffic into classes by fwmark - here we direct traffic into priority class according to
#                                         the fwmark set on the packet (we set fwmark with iptables
#                                         later).  Note that above we've set the default priority
#                                         class to 1:26 so unmarked packets (or packets marked with
#                                         unfamiliar IDs) will be defaulted to the lowest priority
#                                         class.
tc filter add dev imq0 parent 1:0 prio 0 protocol ip handle 20 fw flowid 1:20
tc filter add dev imq0 parent 1:0 prio 0 protocol ip handle 21 fw flowid 1:21

# add MYSHAPER-IN chain to the mangle table in iptables - this sets up the table we'll use
#                                                         to filter and mark packets.
iptables -t mangle -N MYSHAPER-IN
iptables -t mangle -I PREROUTING -i $DEV -j MYSHAPER-IN

# add fwmark entries to classify different types of traffic - Set fwmark from 20-26 according to
#                                                             desired class. 20 is highest prio.
iptables -t mangle -A MYSHAPER-IN -p ! tcp -j MARK --set-mark 20              # Set non-tcp packets to highest priority
iptables -t mangle -A MYSHAPER-IN -p tcp -m length --length :64 -j MARK --set-mark 20 # short TCP packets are probably ACKs
iptables -t mangle -A MYSHAPER-IN -p tcp --dport ssh -j MARK --set-mark 20    # secure shell
iptables -t mangle -A MYSHAPER-IN -p tcp --sport ssh -j MARK --set-mark 20    # secure shell
iptables -t mangle -A MYSHAPER-IN -p tcp --dport telnet -j MARK --set-mark 20 # telnet (ew...)
iptables -t mangle -A MYSHAPER-IN -p tcp --sport telnet -j MARK --set-mark 20 # telnet (ew...)
iptables -t mangle -A MYSHAPER-IN -m mark --mark 0 -j MARK --set-mark 21              # redundant- mark any unmarked packets as 26 (low prio)

# finally, instruct these packets to go through the imq0 we set up above
iptables -t mangle -A MYSHAPER-IN -j IMQ

# Done with inbound shaping 
#
####################################################

echo "Inbound shaping added to $DEV.  Rate: ${RATEDN}Kbit/sec."

Link | Leave a comment | Share

Comments {0}