Using tc to add network latency, jitter, and network reliability

set_network_conditions.bash

#! /bin/bash

# Depends on iproute2 package

INTERFACE="eth0" # This is the network interface being used to send and receive traffic
                 # (if multiple interfaces are being used, must run tc on each)

LATENCY="100ms" # The latency to be artificially added to the connection
                # (only affects outbound packets)
                
LATENCY_JITTER="10ms" # How jitter is set. A random value between +/- $LATENCY_JITTER
                      # Will be added to $LATENCY. In this case let $JITTER = random(-10ms, 10ms)
                      # The artificial latency will be $LATENCY + $JITTER

DROP_PERCENTAGE="1%" # This indicates the percentage of packets which will be artificially dropped

BANDWIDTH="50mbps" # This sets the maximum bandwidth of an interface, in this case 50 Megabytes per second
                   # See the RATES section in tc's man page for the various units supported

if [[ $1 == "RESET" ]]
then
  # Deleting the rule we have previously set reverts the interface back to default
  tc qdisc del dev $INTERFACE root
else
  tc qdisc add dev $INTERFACE root netem delay $LATENCY $LATENCY_JITTER rate $BANDWIDTH loss $DROP_PERCENTAGE
  if [[ $? != 0 ]]
  then
    # if the above command fails, then there must be a rule already set. So replace it instead.
    echo "Replacing pre-existing rule"
    tc qdisc repalce dev $INTERFACE root netem delay $LATENCY $LATENCY_JITTER rate $BANDWIDTH loss $DROP_PERCENTAGE
  fi
fi