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Network Emulation

VILLASnode supports the emulation of wide-area network characteristics.

This emulation can be configured on a per-node basis for outgoing (egress) data only. Incoming data is not processed by the network emulation!

This network emulation is handled by Linux's netem queuing discipline, which is part of the traffic control subsystem. Take a look at the following manual page for supported metrics: tc-netem(8).

VILLASnode only takes care of setting up and initializing the netem queuing discipline inside the kernel. For this, the iproute2 software package (ip & tc commands) must be installed. The configuration is done via the configuration file. Look at etc/example.conf for a section called netem or tc-netem(8) for more details.

Fix for Fedora​

For some reason, Fedora installs the delay distribution profiles under /usr/lib64/tc/, but libnl3 only searches in /usr/lib/tc/. This results in the following error when using netem:

Invalid delay distribution 'normal' in netem config in

To fix this error, please add a symlink: ln -s /usr/lib64/tc /usr/lib/tc

Custom delay distribution​

Netem supports loading custom delay distributions.

  1. Load and compile the netem tools from: https://git.kernel.org/cgit/linux/kernel/git/shemminger/iproute2.git/tree/netem
  2. Create a custom distribution by following the steps described here: https://git.kernel.org/cgit/linux/kernel/git/shemminger/iproute2.git/tree/README.distribution
  3. Put the generated distribution with the suffix .dist in the tc library directory: /usr/lib/tc/.
  4. Load the distribution by specifying the basename in the server configuration.

Further information​

Configuration​

enabled
boolean
Default: true
delay
number
Default: 0

Delay packets in microseconds.

jitter
number (Jitter)
Default: 0

Apply a jitter to the packet delay (in microseconds).

distribution
string (Delay distribution)
Enum: "uniform" "normal" "pareto" "paretonormal"

One of the delay distributions supported by the tc command (see tc-netem(8)).

loss
number (Packet Loss Percentage)
Default: 0

Percentage of packets which will be dropped.

duplicate
number (Packet Duplication Percentage)
Default: 0

Percentage of packets which will be duplicated.

corrupt
number (Packet Corruption Percentage)
Default: 0

Percentage of packets which will be corrupted.

{
  • "enabled": true,
  • "delay": 0,
  • "jitter": 0,
  • "distribution": "uniform",
  • "loss": 0,
  • "duplicate": 0,
  • "corrupt": 0
}

Example

node/etc/examples/nodes/netem.conf
nodes = {
    udp_node = {
        type = "socket"

        format = "gtnet"

        in = {
            address = "127.0.0.1:12001"
        }

        out = {
            address = "127.0.0.1:12000"

            # Network emulation settings
            # Those settings can be specified for each node individually!
            netem = {
                enabled = true

                # Additional latency in microseconds
                delay = 100000

                # Jitter in uS
                jitter = 30000

                # Distribution of delay: uniform, normal, pareto, paretonormal
                distribution = "normal"

                # Packet loss in percent
                loss = 10

                # Duplication in percent
                duplicate = 10

                # Corruption in percent
                corrupt = 10
            }
        }
    }
}