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mahimahi - lightweight, composable network-emulation tools

link emulation: mm-delay, mm-loss, mm-onoff, mm-link

analysis scripts: mm-throughput-graph, mm-delay-graph

observation: mm-meter

record and replay multi-origin websites: mm-webrecord, mm-webreplay


mahimahi is a suite of user-space tools for network emulation and analysis.

Each mahimahi tool spawns a lightweight container, generally connected to the outside via
a synthetic network device that observes packets in transit or emulates a desired

The tools are composable so that a series of emulated network effects can be chained
together, with mahimahi containers nested inside each other. Each tool takes an optional
command to execute, so it is possible to create a series of nested containers with one
command line.


mm-delay delay [command...]

Every packet is delayed by the specified delay (in milliseconds) entering and
leaving the container.

mm-loss uplink|downlink rate [command...]

Packets are lost at the given rate either when leaving (uplink) or entering
(downlink) the container. rate is a number between 0 and 1.

mm-onoff uplink|downlink mean-on-time mean-off-time [command...]

The uplink or downlink will be intermittent and will switch between connected and
disconnected states according to a Poisson point process with specified average
durations spent "on" and "off".

mm-link [--uplink-log=filename] [--downlink-log=filename] [--meter-uplink] [--meter-
uplink-delay] [--meter-downlink] [--meter-downlink-delay] [--once] uplink-filename
downlink-filename [command...]


Emulates a throughput-limited link with a specified packet-delivery
schedule and analyzes the resulting performance. See mm-link(1).


mm-meter [--meter-uplink] [--meter-downlink] [command...]

Displays an animated live plot of the transfer rate entering or leaving the


mm-webrecord directory [command...]

Transparently proxies outgoing HTTP and HTTPS connections, saving the
requests, corresponding responses, and IP address of each Web server
contacted in the given directory. mm-webrecord uses a self-signed TLS
certificate in its HTTPS proxy, causing typical Web browsers to reject it.
For testing or debugging purposes, this behavior can usually be turned off,
e.g.: with the --no-check-certificate option to wget(1) or the --ignore-
certificate-errors option to chromium-browser(1).

mm-webreplay directory [command...]

Replays a saved session from a previous run of mm-webrecord. Unlike most
mahimahi tools, the mm-webreplay container does not have a network connection
to the outside world. Instead, it has dummy network interfaces bound to each
IP address on which a Web server in the saved session had answered a request.
mm-webreplay runs an apache2(8) Web server bound to each such IP address
inside the container. Each Web server emulates the corresponding server from
the saved session. When receiving a request that matches one in the
directory, the corresponding apache2 replies with the same reply as
previously captured.

mm-webreplay can be used to measure the performance of Web browsers on
complex websites and the effect of changes in Web protocols (e.g. HTTP,
HTTP/2, SPDY, QUIC). Unlike tools like web-page-replay, mm-webreplay
preserves the sharded structure of a website, binds to the actual IP
addresses that the real website used, and serves requests from real Web


The MAHIMAHI_BASE environment variable is set to an IP address of the host, outside any
container. This can be used to conduct scripted measurements over a series of mahimahi
containers chained together.


To spawn a shell with a delayed, lossy link to the Internet:

$ mm-delay 50 mm-loss uplink 0.2
[delay 50 ms] [loss up=0.1] $

To run ping over the same link:

$ mm-delay 50 mm-loss uplink 0.2 sh -c 'ping -c 10 -n $MAHIMAHI_BASE'
PING ( 56(84) bytes of data.
64 bytes from icmp_seq=1 ttl=63 time=101 ms
64 bytes from icmp_seq=2 ttl=63 time=100 ms
64 bytes from icmp_seq=4 ttl=63 time=101 ms
64 bytes from icmp_seq=5 ttl=63 time=100 ms
64 bytes from icmp_seq=7 ttl=63 time=101 ms
64 bytes from icmp_seq=8 ttl=63 time=101 ms
64 bytes from icmp_seq=9 ttl=63 time=101 ms
64 bytes from icmp_seq=10 ttl=63 time=101 ms

--- ping statistics ---
10 packets transmitted, 8 received, 20% packet loss, time 8999ms
rtt min/avg/max/mdev = 100.910/101.009/101.092/0.279 ms

To record a page load from www.nytimes.com:

$ mm-webrecord /tmp/nytimes chromium-browser --ignore-certificate-errors --user-data-dir=/tmp/nonexistent$(date +%s%N) www.nytimes.com

The use of --user-data-dir=/tmp/nonexistent$(date +%s%N) is to prevent the browser
from reusing an existing chromium-browser process.

To make Chrome retrieve the saved website over a delayed, lossy link whose throughput is
limited to 1 full-sized packet per millisecond:

$ mm-webreplay /tmp/nytimes mm-delay 50 mm-loss uplink 0.1 mm-link <(echo 1) <(echo 1) -- chromium-browser --ignore-certificate-errors --user-data-dir=/tmp/nonexistent$(date +%s%N) www.nytimes.com

To emulate a variable cellular network and visualize a process's use of the network:

$ mm-delay 20 mm-link --meter-all /usr/share/mahimahi/traces/Verizon-LTE-short.up /usr/share/mahimahi/traces/Verizon-LTE-short.down
[delay 20 ms] [link] $

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