network congestion steps (latency and loss) for linux (iptables and tc)

network_congestion_linux.sh

#!/bin/sh

remove_rules()
{

	echo "removing iptables and tc rules"
	sudo iptables -F
	echo "removing tc qdisc for ${netif}"
	sudo tc qdisc del dev ${netif} root

}

ctrl_c()
{
	# remove rules
	remove_rules

	# exit
	exit 0
}

trap ctrl_c INT

ip="${2}"
netif="${1}"
cycle_duration_seconds=120
rejected_step_percent=5
rejected_step_current_percent=85
latency_step_ms=500
latency_max=4000
latency_first=500
latency_current=${latency_first}

if [[ -z "${ip}" ]]
then
	echo "An IP Address is required as the second argument."
	exit 1
fi

if [[ -z "${netif}" ]]
then
	echo "An interface name is required as the first argument."
	exit 1
fi

duration=0
((duration=${cycle_duration_seconds}*(${latency_max}/${latency_step_ms})))

echo "Executing network congestion for ${ip}"
echo -e "\tduration per rejected packet step: ${rejected_step_current_percent}% to 0% at ${rejected_step_percent}%: ${duration}s"
echo -e "\tlatency range per rejected packet step: ${latency_current}ms to ${latency_max}ms at ${latency_step_ms}ms per latency step"
echo -e "\tTest your network code during this time, the levels are printed to the console to allow you to repeat network conditions that cause problems and fix them."
echo ""

while [[ "$rejected_step_current_percent" > "0" ]]
do
	# drop % of traffic through range

	remove_rules

	if [[ "${rejected_step_current_percent}" == "100" ]]
	then

		# from IP
		sudo iptables -I INPUT -m statistic --mode random --probability 1 -s ${ip} -j REJECT
		# to IP
		sudo iptables -I OUTPUT -m statistic --mode random --probability 1 -d ${ip} -j REJECT

	else

		# from IP
		sudo iptables -I INPUT -m statistic --mode random --probability 0.${rejected_step_current_percent} -s ${ip} -j REJECT
		# to IP
		sudo iptables -I OUTPUT -m statistic --mode random --probability 0.${rejected_step_current_percent} -d ${ip} -j REJECT
	fi

	while [[ ${latency_current} -lt ${latency_max} ]]
	do

		# set latency through range

		# remove existing queues
		echo "removing tc qdisc for ${netif}"
		sudo tc qdisc del dev ${netif} root

		sudo tc qdisc add dev ${netif} root handle 1: prio
		sudo tc qdisc add dev ${netif} parent 1:3 handle 30: netem delay ${latency_current}ms
		sudo tc filter add dev ${netif} protocol ip parent 1:0 prio 3 u32 match ip dst ${ip} flowid 1:3
		sudo tc filter add dev ${netif} protocol ip parent 1:0 prio 3 u32 match ip src ${ip} flowid 1:3

		echo "latency: ${latency_current}ms with ${rejected_step_current_percent}% traffic rejected to and from ${ip} for ${cycle_duration_seconds} seconds."

		# wait for the cycle
		sleep ${cycle_duration_seconds}

		# increase the step value of latency
		((latency_current=${latency_current}+${latency_step_ms}))

	done

	# increase the step value of drop percent
	((rejected_step_current_percent=${rejected_step_current_percent}+${rejected_step_percent}))

	# reset latency step to first value
	latency_current=${latency_first}

done

remove_rules