Linux Traffic Control

Using the tc (traffic control) utility in Linux, it is possible to simulate various network conditions, such as latency, packet loss, random conditions, etc.

List existing tc rules:

sudo /usr/sbin/tc -p qdisc ls dev eth0

Delete existing tc rules:

sudo /usr/sbin/tc -p qdisc del dev eth0 root

Add vs. Change

If a rule does not already exist, use the add command option:

sudo /usr/sbin/tc qdisc add dev eth0 root netem delay 10ms

If a rule already exists, use the change command option:

sudo /usr/sbin/tc qdisc change dev eth0 root netem delay 10ms

Simple Delay / Latency

Add 10ms of delay / latency:

sudo /usr/sbin/tc qdisc add dev eth0 root netem delay 10ms

This command simply adds 10ms of delay:

[email protected]:~$ ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_seq=1 ttl=57 time=1.57 ms
64 bytes from 8.8.8.8: icmp_seq=2 ttl=57 time=1.37 ms
64 bytes from 8.8.8.8: icmp_seq=3 ttl=57 time=1.29 ms
64 bytes from 8.8.8.8: icmp_seq=4 ttl=57 time=1.29 ms
64 bytes from 8.8.8.8: icmp_seq=5 ttl=57 time=1.25 ms
64 bytes from 8.8.8.8: icmp_seq=6 ttl=57 time=11.4 ms
64 bytes from 8.8.8.8: icmp_seq=7 ttl=57 time=11.4 ms
64 bytes from 8.8.8.8: icmp_seq=8 ttl=57 time=11.4 ms
64 bytes from 8.8.8.8: icmp_seq=9 ttl=57 time=11.3 ms
64 bytes from 8.8.8.8: icmp_seq=10 ttl=57 time=11.5 ms
64 bytes from 8.8.8.8: icmp_seq=11 ttl=57 time=11.4 ms
64 bytes from 8.8.8.8: icmp_seq=12 ttl=57 time=1.31 ms
64 bytes from 8.8.8.8: icmp_seq=13 ttl=57 time=1.43 ms
64 bytes from 8.8.8.8: icmp_seq=14 ttl=57 time=1.35 ms
64 bytes from 8.8.8.8: icmp_seq=15 ttl=57 time=1.32 ms

Random Delay / Latency

sudo /usr/sbin/tc qdisc add dev eth0 root netem delay 20ms 10ms 25%

This command adds 20ms of delay, randomizes by +/- 10ms with a 25% variance:

[email protected]:~$ ping 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_seq=1 ttl=57 time=1.57 ms
64 bytes from 8.8.8.8: icmp_seq=2 ttl=57 time=1.35 ms
64 bytes from 8.8.8.8: icmp_seq=3 ttl=57 time=1.35 ms
64 bytes from 8.8.8.8: icmp_seq=4 ttl=57 time=1.29 ms
64 bytes from 8.8.8.8: icmp_seq=5 ttl=57 time=1.42 ms
64 bytes from 8.8.8.8: icmp_seq=6 ttl=57 time=11.9 ms
64 bytes from 8.8.8.8: icmp_seq=7 ttl=57 time=17.2 ms
64 bytes from 8.8.8.8: icmp_seq=8 ttl=57 time=19.5 ms
64 bytes from 8.8.8.8: icmp_seq=9 ttl=57 time=27.4 ms
64 bytes from 8.8.8.8: icmp_seq=10 ttl=57 time=28.8 ms
64 bytes from 8.8.8.8: icmp_seq=11 ttl=57 time=30.1 ms
64 bytes from 8.8.8.8: icmp_seq=12 ttl=57 time=20.5 ms
64 bytes from 8.8.8.8: icmp_seq=13 ttl=57 time=19.10 ms
64 bytes from 8.8.8.8: icmp_seq=14 ttl=57 time=12.9 ms
64 bytes from 8.8.8.8: icmp_seq=15 ttl=57 time=14.7 ms
64 bytes from 8.8.8.8: icmp_seq=16 ttl=57 time=20.6 ms
64 bytes from 8.8.8.8: icmp_seq=17 ttl=57 time=16.7 ms
64 bytes from 8.8.8.8: icmp_seq=18 ttl=57 time=16.10 ms
64 bytes from 8.8.8.8: icmp_seq=19 ttl=57 time=22.9 ms
64 bytes from 8.8.8.8: icmp_seq=20 ttl=57 time=26.9 ms
64 bytes from 8.8.8.8: icmp_seq=21 ttl=57 time=25.8 ms
64 bytes from 8.8.8.8: icmp_seq=22 ttl=57 time=17.3 ms
64 bytes from 8.8.8.8: icmp_seq=23 ttl=57 time=22.7 ms
64 bytes from 8.8.8.8: icmp_seq=24 ttl=57 time=20.2 ms
64 bytes from 8.8.8.8: icmp_seq=25 ttl=57 time=29.7 ms
64 bytes from 8.8.8.8: icmp_seq=26 ttl=57 time=30.4 ms
64 bytes from 8.8.8.8: icmp_seq=27 ttl=57 time=13.5 ms
64 bytes from 8.8.8.8: icmp_seq=28 ttl=57 time=29.3 ms
64 bytes from 8.8.8.8: icmp_seq=29 ttl=57 time=26.4 ms
64 bytes from 8.8.8.8: icmp_seq=30 ttl=57 time=12.6 ms
64 bytes from 8.8.8.8: icmp_seq=31 ttl=57 time=1.29 ms
64 bytes from 8.8.8.8: icmp_seq=32 ttl=57 time=1.43 ms
64 bytes from 8.8.8.8: icmp_seq=33 ttl=57 time=1.30 ms
64 bytes from 8.8.8.8: icmp_seq=34 ttl=57 time=1.36 ms

Random packet loss

sudo /usr/sbin/tc qdisc change dev eth0 root netem loss 10% 25%

This command simulates 10% packet loss with a 25% probability of successive loss:

                              My traceroute  [v0.92]
shell (104.131.191.87)                                            2020-05-04T23:52:38+0000
Keys:  Help   Display mode   Restart statistics   Order of fields   quit
                                                 Packets               Pings
 Host                                            Loss%   Snt   Last   Avg  Best  Wrst StDev
 1. 104.131.0.254                                1.2%    82    0.4   1.4   0.4  20.2   3.0
 2. 138.197.248.6                                0.0%    82    8.8   1.2   0.5  23.0   2.9
 3. 138.197.244.44                               1.2%    82    1.0   1.3   0.9   5.7   0.8
 4. 162.243.191.243                              1.2%    82    3.3   1.4   1.0   8.5   1.1
 5. 108.170.248.97                               0.0%    82    1.5   1.4   1.3   1.7   0.1
 6. 172.253.72.129                               0.0%    81    1.5   1.5   1.4   1.8   0.1
 7. lga34s15-in-f14.1e100.net                    2.5%    81    1.4   1.5   1.4   1.6   0.1

Using tc to manipulate performance testing with iperf3

Baseline test with no tc rules applied:

[email protected]:~$ iperf3 -t 10 -i 1 -c 128.252.5.113
Connecting to host 128.252.5.113, port 5201
[  5] local 104.131.191.87 port 43942 connected to 128.252.5.113 port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec  62.9 MBytes   527 Mbits/sec    3   5.49 MBytes
[  5]   1.00-2.00   sec  82.5 MBytes   692 Mbits/sec    0   5.49 MBytes
[  5]   2.00-3.00   sec  82.5 MBytes   692 Mbits/sec    0   5.49 MBytes
[  5]   3.00-4.00   sec  81.2 MBytes   682 Mbits/sec    0   5.49 MBytes
[  5]   4.00-5.00   sec  82.5 MBytes   692 Mbits/sec    0   5.49 MBytes
[  5]   5.00-6.00   sec  81.2 MBytes   682 Mbits/sec    0   5.49 MBytes
[  5]   6.00-7.00   sec  82.5 MBytes   692 Mbits/sec    0   5.49 MBytes
[  5]   7.00-8.00   sec  81.2 MBytes   682 Mbits/sec    0   5.49 MBytes
[  5]   8.00-9.00   sec  82.5 MBytes   692 Mbits/sec    0   5.49 MBytes
[  5]   9.00-10.00  sec  82.5 MBytes   692 Mbits/sec    0   5.49 MBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec   802 MBytes   672 Mbits/sec    3             sender
[  5]   0.00-10.04  sec   801 MBytes   669 Mbits/sec                  receiver

iperf Done.

sudo /usr/sbin/tc qdisc add dev eth0 root netem loss 10% 25%

Applying 10% packet loss:

[email protected]:~$ iperf3 -t 10 -i 1 -c 128.252.5.113
Connecting to host 128.252.5.113, port 5201
[  5] local 104.131.191.87 port 43946 connected to 128.252.5.113 port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec  1.28 MBytes  10.7 Mbits/sec    4   22.6 KBytes
[  5]   1.00-2.00   sec   764 KBytes  6.26 Mbits/sec    5   22.6 KBytes
[  5]   2.00-3.00   sec   764 KBytes  6.26 Mbits/sec    6   22.6 KBytes
[  5]   3.00-4.00   sec   382 KBytes  3.13 Mbits/sec    8   11.3 KBytes
[  5]   4.00-5.00   sec   382 KBytes  3.13 Mbits/sec    4   17.0 KBytes
[  5]   5.00-6.00   sec   382 KBytes  3.13 Mbits/sec   10   14.1 KBytes
[  5]   6.00-7.00   sec   382 KBytes  3.13 Mbits/sec    4   21.2 KBytes
[  5]   7.00-8.00   sec   764 KBytes  6.26 Mbits/sec    6   12.7 KBytes
[  5]   8.00-9.00   sec   382 KBytes  3.13 Mbits/sec    4   25.5 KBytes
[  5]   9.00-10.00  sec   382 KBytes  3.13 Mbits/sec    9   12.7 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec  5.76 MBytes  4.83 Mbits/sec   60             sender
[  5]   0.00-10.04  sec  5.08 MBytes  4.25 Mbits/sec                  receiver

iperf Done.

sudo /usr/sbin/tc qdisc change dev eth0 root netem delay 100ms 10ms 25%

Adding 100ms of latency:

[email protected]:~$ iperf3 -t 10 -i 1 -c 128.252.5.113
Connecting to host 128.252.5.113, port 5201
[  5] local 104.131.191.87 port 43950 connected to 128.252.5.113 port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec  4.09 MBytes  34.3 Mbits/sec    4    543 KBytes
[  5]   1.00-2.00   sec  18.8 MBytes   157 Mbits/sec    0   4.35 MBytes
[  5]   2.00-3.00   sec  26.2 MBytes   220 Mbits/sec    0   4.35 MBytes
[  5]   3.00-4.00   sec  22.5 MBytes   189 Mbits/sec    0   4.35 MBytes
[  5]   4.00-5.00   sec  22.5 MBytes   189 Mbits/sec    0   4.35 MBytes
[  5]   5.00-6.00   sec  26.2 MBytes   220 Mbits/sec    0   4.35 MBytes
[  5]   6.00-7.00   sec  23.8 MBytes   199 Mbits/sec    0   4.35 MBytes
[  5]   7.00-8.00   sec  25.0 MBytes   210 Mbits/sec    0   4.35 MBytes
[  5]   8.00-9.00   sec  26.2 MBytes   220 Mbits/sec    0   4.35 MBytes
[  5]   9.00-10.00  sec  26.2 MBytes   220 Mbits/sec    0   4.35 MBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec   222 MBytes   186 Mbits/sec    4             sender
[  5]   0.00-10.13  sec   219 MBytes   182 Mbits/sec                  receiver

iperf Done.

There are a lot more examples here and here.


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