Hello World

The hello world topology is a network of two interconnected nodes named hello and world.

import mergexp as mx

# create a topology named 'hello-world'

net = mx.Topology('hello-world')

# define two nodes hello and world

hello = net.device('hello')

world = net.device('world')

# connect hello and world

link = net.connect([hello, world])

# access endpoint by link operator

link[hello].ip.addrs = ['10.0.0.1/24']

link[world].ip.addrs = ['10.0.0.2/24']

# specify the net object as the experiment topology created by this script

mx.experiment(net)

This example shows the 3 basic modeling components in the Merge experiment modeling library

• Topology: contains devices interconnected by links.
• Device: a member of a network.
• Link: interconnects devices.

Topologies

A topology object is the structural model of an experiment. It contains the devices in an experiment and the links that interconnect them. Topology constructors take a single argument that is the name of the topology.

net = mx.Topology('hello-world')

Devices

Device objects are the nodes in your experiment network. In this case we have two devices 'hello' and 'world'. This example shows the simplest way to create a device, which is just to give it a name. Later examples will show how constraints can be used to specify specific property requirements about devices such as number of CPU cores and amount of memory.

hello = net.device('hello')

world = net.device('world')

Links

Link objects interconnect devices. The link constructor takes in a list of devices as the only required parameter. In this example we only provide two devices, so what we wind up with is a point to point link. Two is the minimum number of devices that may be supplied to a link, however there is no upper limit on the number of devices. Links with more than two devices are called multipoint links and are explained in a later example.

link = net.connect([hello, world])

Like devices links can also take constraint based properties such as delay and capacity limiting. Later examples will demonstrate link modeling in detail.

IP Addressing

One thing to notice about this topology is how IP addresses are assigned to nodes. IP addresses are assigned to endpoint objects, and the number of endpoints a given node has depends on how many links are connected to it. In this example we created a single link between the two nodes, so each node has one endpoint. We can access the endpoint through the link object by indexing over the node, this is demonstrated in the example code as

link[hello].ip.addrs = ['10.0.0.1/24']

link[world].ip.addrs = ['10.0.0.2/24']

Notice also that IP addresses are assigned to endpoints as lists, so there can be any number of IP addresses assigned to a given endpoint.

Experiment Entry Point

In order for an experiment script to be used by MergeTB, you must specify the topology object to be used. Because experiment scripts are simply python files, there could be a number of topology objects in the script, so you need to let merge know which one to use. This is the purpose of the final line

Complete Example

mx.experiment(net)