Use 'tc netem' to set delay/latency and loss parameters on an interface

cfg_delayer.sh

#!/bin/bash

usage()
{
cat << EOF
USAGE: $0 [-hc] [-a <adapter>] [-d <delay-param>] [-l <loss-param>]
OPTIONS:
   -h           Show this message
   -a <adapter> Set the adapter
   -d <delay>   Set delay/latency parameters (as accepted by netem[1])
   -l <loss>    Set loss parameters (as accepted by netem[1])

[1]: https://wiki.linuxfoundation.org/networking/netem

EXAMPLES:
   $0 -a eth0 -d 100ms ... set latency 100ms
   $0 -a eth0 -d "100ms 10ms 25%" ... set latency 100ms, +/-10ms, with next random element depending 25% on prev one.
   $0 -a eth0 -l 0.1% ... causes 1/10th of a percent (i.e 1 out of 1000) packets to be randomly dropped.
   $0 -a eth0 -l 0.3% 25% ... cause 0.3% pkt lost, and successive probability depends by a quarter of last one.
   $0 -c -a eth0 ... clear all config
EOF
    exit 1
}

clear_cfg()
{
    # Delete existing settings
    tc qdisc del dev $IFACE root
    [[ "$MODE" == "clear" ]] && echo "cleared config" && exit 0
}

while getopts ha:l:d:c o
do  case "$o" in
    h)  usage
        exit 1;;
    d)      DELAY_PARAM=$OPTARG;;
    l)      LOSS_PARAM=$OPTARG;;
    a)      IFACE=$OPTARG;;
    c)      MODE="clear";;
    [?])    usage
    esac
done

[[ "$IFACE" == "" ]] && echo "Need interface" && usage
ip link show "$IFACE" > /dev/null
[[ $? -ne 0 ]] && echo "do not have link [$IFACE]" && usage

clear_cfg

CMD=""
[[ "$DELAY_PARAM" != "" ]] && CMD="$CMD delay $DELAY_PARAM"
[[ "$LOSS_PARAM" != "" ]] && CMD="$CMD loss $LOSS_PARAM"
tc qdisc add dev $IFACE root netem $CMD