ipfw jitter test script

jitter.sh

#!/bin/bash

MIN_LAG=25
MAX_LAG=50
(( LAG_RANGE = MAX_LAG - MIN_LAG ))

TIME=600 # total test time (in seconds)
INTERVAL=0.1 # time in between changes in latency (in seconds)
STEPS=6000 # TIME / INTERVAL

# set up a pipe to add latency, which matches only *incoming*
# traffic from the localhost to the localhost
ipfw add 100 pipe 1 ip from 127.0.0.1 to 127.0.0.1 in
ipfw add 100 allow ip from 127.0.0.1 to 127.0.0.1 out

# set up initial random delay
(( delay = RANDOM % LAG_RANGE + MIN_LAG ))
echo "setting delay to" $delay "ms"

ipfw pipe 1 config delay ${delay}ms

# start ping background process and stash result in a file
ping -i 0.05 localhost > ping_out &
PING_PID=$! # remember the PID so we can kill it later

for ((i=0; i < STEPS; i++))
do
    sleep $INTERVAL

    # change the delay to a new random value
    (( delay = RANDOM % LAG_RANGE + MIN_LAG ))
    ipfw pipe 1 config delay ${delay}ms

    echo "setting delay to" $delay "ms"
done

# kill the ping process
kill $PING_PID

# remove the pipe and the associated rule
ipfw delete 100
ipfw pipe 1 delete