tcp_throttle uses packet shaping to add delay to specific packets

tcp_throttle.sh

#!/bin/bash

# this uses packet shaping to add delay to specific packets.
# for more informatino about "netem" the network emulation module 
# see http://www.linuxfoundation.org/collaborate/workgroups/networking/netem
# or http://lartc.org/howto/index.html section 9 and 12
# please add more options to this script as needed.

function usage() {
    echo "USAGE: $(basename $0) --interface=<ethX> (--dport=<PORT> | --host=<IP>) --delay=<DELAY_SPEC> --start"
    echo "       $(basename $0) --interface=<ethX> (--stop | --status)"
    echo "       DELAY_SPEC examples: '100ms 10ms', '3000ms 2000ms distribution normal'"
    exit 1
}

port=""
delay="100ms"
dev="lo"
host=""

while [ "$1" != "" ]; do
    param=${1%%=*}
    value=${1#*=}
    case $param in
        --dport)
            port="dport $value  0xffff"
            ;;
        --host)
            host="dst $value"
            ;;
        --delay)
            delay=$value
            ;;
        --interface)
            dev=$value
            ;;
        --start)
            START=1
            ;;
        --stop)
            STOP=1
            ;;
        --status)
            STATUS=1
            ;;
        --help | -h)
            usage
            ;;
        *)
           echo "ERROR: bad argument '$1'"
           usage
           ;;
    esac
    shift
done

if [ -n "$host" ] && [ -n "$port" ]; then
    echo "ERROR: you can only use --host or --dport, not both"
    usage
fi
if [ $(expr ${START:-0} + ${STOP:-0} + ${STATUS:-0}) != 1 ] ; then
    echo "ERROR: use exactly one of --start --stop --status"
    usage
fi

if [ -n "$STATUS" ]; then
    /sbin/tc -s qdisc
    /sbin/tc filter show dev $dev
fi

if [ -n "$START" ]; then
    echo "delaying $host $port on interface $dev for $delay"
    /sbin/tc qdisc del dev $dev root 2>/dev/null
    /sbin/tc qdisc add dev $dev root handle 1: prio
    /sbin/tc filter add dev $dev protocol ip parent 1: prio 1 u32 match ip $host $port flowid 1:3
    /sbin/tc qdisc add dev $dev parent 1:3 handle 31: netem delay $delay
fi

if [ -n "$STOP" ]; then
    /sbin/tc qdisc del dev $dev root
fi