This bash script artificially limits bandwidth, delay and loss rate on selected interfaces. It allows traffic shaping on both downlink and uplink. It can enforce shaping on multiple interfaces at a time.

For information and suggestions please write to: martino.trevisan@polito.it

This is a bash script to be used in a Linux environment. It depends on the the package tc. Under the hood it uses the kernel module ifb.

Warning: if you are using nftables, traffic shaping on the Docker interfaces might not work due to routing/NAT issues.

To start traffic shaping, you can run:

sudo ./network_emulator.sh <iface>:<downspeed>:<upspeed>:<rtt>:<loss>

where:

• <iface> is the target physical interface you want to alterate
• <downspeed> is the downlink capacity. Unit must be present, e.g., 20mbit.
• <upspeed> is the uplink capacity. Unit must be present, e.g., 10mbit.
• <rtt> is the RTT. Unit must be present, e.g., 50ms. It is enforced on the uplink.
• <loss> is the loss probability. Must be followed by %, e.g., 10%. Enforced on both up and down link.

You can write multiple <iface>:<downspeed>:<upspeed>:<rtt>:<loss> to configure shaping on multiple interfaces. Under the hood it creates multiple virtual ifb interfaces to shape both down and uplink traffic.

You can omit one or more of <downspeed>, <upspeed>, <rtt>, <loss> to avoid enforcing shaping for those parameters. E.g., you can write a command for enforcing only RTT with: <iface>:::<rtt>:, like wlan0:::50ms:.

To remove all traffic shaping rules, use:

sudo ./network_emulator.sh remove

1. Enforce 20mbit download, 5mbit upload, 20ms RTT and no packet loss on eth0.

sudo ./network_emulator.sh eth0:20mbit:5mbit:20ms:0%

2. Enforce 100ms RTT on eth0.

sudo ./network_emulator.sh eth0:::20ms:

Note that you can omit parameters that you don't want to shape.

3. Enforce 1% packet loss on docker0, docker1 and docker2 (if you are using docker container engine)

sudo ./network_emulator.sh docker0::::1% docker1::::1% docker2::::1%