Traffic control - Make DNS requests delayed and low priority on Linux

tc-delaydnsreqs.sh

#!/bin/sh
# SPDX-License-Identifier: MIT

## Copyright (C) 2017 Przemyslaw Pawelczyk <przemoc@gmail.com>
##
## This script is licensed under the terms of the MIT license.
## https://opensource.org/licenses/MIT
#
# Traffic control - Make DNS requests delayed and low priority on Linux.

if [ $# -eq 0 ] || [ "$1" = "-h" ] || [ "$1" = "--help" ]; then
	echo "Usage: $0 IFACE [DELAY [JITTER [CORRELATION]]]"
	echo
	echo "Example: $0 eth1 500ms 100ms"
	exit 0
fi

IFACE=$1
shift

ip link show dev $IFACE >/dev/null || exit 1

tc qdisc del dev $IFACE root 2>/dev/null

if [ -z "$*" ] || [ "$1" = "off" ]; then
	echo "Traffic control: Set default queueing discipline on $IFACE."
	exit 0
fi

echo "Traffic control: Make DNS requests delayed and low priority on $IFACE."

tc qdisc  add dev $IFACE root handle 1: \
   prio bands 2 priomap 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

tc qdisc  add dev $IFACE parent 1:2 handle 53: \
   netem delay "$@"

tc filter add dev $IFACE parent 1:  \
   protocol ip prio 1 u32 match ip dport 53 0xffff flowid 1:2

I haven't used this, but right away this seems like a great way to demonstrate just how influential DNS performance can be to a web browsing overall. I've had difficulty explaining just how many DNS requests are made per page load, and conveying just how important DNS performance can be. This would be a wonderful way to demonstrate it. Starred.

@naikrovek Yeah, slow or malfunctioning DNS can literally kill your web experience. It was meant to help test/debug software that may expect DNS replies within short timeframe, which is not always the case.

commit a11585efc32ce26b8b51dcc5ba4eb5e9034d2dd3
Author: Przemyslaw Pawelczyk <przemoc@gmail.com>
Date:   2018-02-06 14:59:01 +0100

    tc-delaydnsreqs.sh: Add copyright notice and MIT license notice.

commit 84b514c728bc3bbf49158393dad3d5ba926557ea
Author: Przemyslaw Pawelczyk <przemoc@gmail.com>
Date:   2018-02-06 14:59:47 +0100

    Add SPDX License Identifier.

    The Software Package Data Exchange (SPDX) is a good initiative, it has
    matured over time and deserves accelerated adoption in open-source.

    https://spdx.org/learn
    https://spdx.org/using-spdx
    https://spdx.org/license-list