Bash script to selectively slow down traffic to given IP's - using tc netem

slow_network.sh

#!/bin/bash
set -e
set -u
set -o pipefail

IFACE="lo"
LATENCY=200

CLEAN=""
IPS=()
for i in "$@"; do
    case $i in
        --help)
            cat <<EOF
Usage:

    ./slow_network.sh [--clean] [--iface=IFACE] [--latency=LATENCYMS] [ADDRESS]...

Cleans and sets a tc (traffic control) policy on a given IFACE, adding
latency on traffic going to specific IP addresses. The script first
cleans up existing tc policy, and sets up a simple netem/u32
configuration.

By default the IFACE=lo and LATENCYMS=200. IFACE can also be set to a
"default" string which will cause the script to resolve the default
gateway and use the appropriate interface.

When ADDRESSES are not given over command line, they are read from
stdin until EOF.

The --clean option just clears the tc config.

Example:

    $ sudo ./slow_network.sh --interface=default 1.1.1.1 8.8.8.8
    [ ] Setting tc on enx381428a758c2, latency 200 ms
    $ ping -nc2 1.1.1.1
    PING 1.1.1.1 (1.1.1.1) 56(84) bytes of data.
    64 bytes from 1.1.1.1: icmp_seq=1 ttl=64 time=201 ms
    64 bytes from 1.1.1.1: icmp_seq=2 ttl=64 time=201 ms

If IFACE is lo, then the LATENCY might be doubled since both ingress
and egress go via tc::

   $ sudo ./slow_network.sh --latency=100 ::1 127.0.0.1
   [ ] Setting tc on lo, latency 100 ms
   $ ping -nc2 127.0.0.1
   PING 127.0.0.1 (127.0.0.1) 56(84) bytes of data.
   64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=200 ms
   64 bytes from 127.0.0.1: icmp_seq=2 ttl=64 time=200 ms

You can give the script a hostname to resolve:

   $ sudo ./slow_network.sh --iface=default speed.cloudflare.com
   [ ] Setting tc on enxf6beece96820, latency 200 ms
    - 104.18.47.225
    - 172.64.156.31
    - 2606:4700:440e::6812:2fe1
    - 2606:4700:440e::ac40:9c1f
EOF
            exit 1
            ;;
        --clean|--clear)
            CLEAN="yes"
            shift # past argument with no value
            ;;
        -i=*|--interface=*|--iface=*)
            IFACE="${i#*=}"
            shift
            ;;
        -l=*|--latency=*)
            LATENCY="${i#*=}"
            shift
            ;;
        -*|--*)
            echo "Unknown option $i"
            exit 1
            ;;
        *)
            IPS[${#IPS[@]}]="$i"
            shift
            ;;
    esac
done

if [ "$IFACE" == "default" ]; then
    IFACE=`ip r show default|awk '/default/ {print $5}'|head -n1`
fi

if [ "$CLEAN" == "yes" ]; then
    echo "[ ] Cleaning up tc on $IFACE"
    tc qdisc del dev $IFACE root
    exit 0
fi

echo "[ ] Setting tc on $IFACE, latency $LATENCY ms"

tc qdisc del dev $IFACE root || true
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 1:1 handle 2: fq_codel
tc qdisc add dev $IFACE parent 1:2 handle 3: netem delay ${LATENCY}ms

if [ "${#IPS[@]}" -gt "0" ]; then
    for LINE in "${IPS[@]}"; do
        echo $LINE
    done
else
    while read LINE; do
        echo $LINE
    done
fi | while read IP; do
    echo $IP | \
        python3 -c "import socket as s;print('\n'.join(x[4][0] for x in s.getaddrinfo(input(), 0, 0,s.SOCK_STREAM)))" \
        | while read XIP; do
        echo " - $XIP"
        if [[ "$XIP" =~ .*":".* ]]; then
            tc filter add dev $IFACE protocol ipv6 parent 1:  u32 match ip6 dst $XIP flowid 1:2
        else
            tc filter add dev $IFACE protocol ip parent 1: prio 1 u32 match ip dst $XIP flowid 1:2
        fi
    done
done