This is a network simulator that can work in one of two ways:

• As a UDP proxy server, where a proxy port stands in for the real port and packets are forwarded to the server and back to the client.
• As a Linux NFQUEUE implementation, handling all incoming and outgoing packets on a given port.

Both of these share the same set of network simulation parameters and behaviors, abstracting the concept of a packet from IP and UDP.

apt-get install libnetfilter-queue-dev
pip install .

Set MTU on the loopback device to something small. This is also required for bandwidth throttling to work correctly with NFQUEUE:

ip link show dev lo  # show current MTU (2 ** 16 by default)
ip link set dev lo mtu 2048  # reset on next restart

In addition, this package will install several scripts into PATH:

• impaired_network_server which starts up an impaired network and an API server to communicate with the network
• impaired_network_shell which starts up an impaired network and an external shell to communicate with the network
• impaired_network_clear_ip_tables resets iptables and removes all impaired network rules

You can run most of the tests like this:

python -m unittest discover tests  # run all tests in the tests/ directory

Some of the end-to-end tests will be skipped with the above command because they require root:

sudo python tests/test_e2e.py

There's an interactive mode where you can change settings on the fly inside a Python shell. Right now it support constant-probability packet loss and constant packet delay.

For a simple UDP application to test, you can use the QUIC server and client from Chromium.

Then run the proxy. This command proxies a UDP server running on local port 6121, using 6122 as the proxy port:

impaired_network_shell -l user -t udp -p 6121 -x 6122

The NFQUEUE implementation has the same interactive interface as the UDP proxy. This command handles packets to/from a local TCP server running on port 8000:

sudo impaired_network_shell -l kernel -t tcp -p 8000