2.1 Ethernet Links

Connecting simulated machines over a simulated Ethernet connection is done by creating a link using one of the components in the eth-links module: ethernet-cable, ethernet-hub or ethernet_switch. Any of these components can connect to the Ethernet devices of the simulated machines. They model Ethernet at the frame level, in that they perform delivery of complete frames sent from one device to another, and do not model collisions or lower-level signaling details. Each of the three Ethernet links has its own particularities:

ethernet_cable An Ethernet cable can only be connected to two devices, since, as a real Ethernet cable, it only has two ends. Apart from transporting Ethernet frames back and forth, an Ethernet cable models whether the signal is up or down.
ethernet_hub An ethernet_hub is the simplest Ethernet link model: all frames are broadcast to all devices connected to the hub. It works like a traditional hub or coaxial cable.
ethernet_switch An ethernet_switch also allows the connection of multiple devices, but functions rather like a switch: as it learns what MAC addresses the different devices have, it stops broadcasting and transports the frame more selectively. This can substantially improve simulation performance when several devices are talking on the link, and even more so when the simulation is distributed.

As all three models work more or less at the frame level; they can be used for any type of Ethernet connection, without limitations due to speed or technology. Traffic sent over the link can be anything, including TCP/IP or any other protocol stack that works on top of Ethernet. The link does not need to be configured for the intended use.

The three components are provided in the eth-links module. They can be manipulated in the same way as any other component: after loading eth-links, the create-ethernet-cable/hub/switch commands are made available. They create non-instantiated components:

The name will be automatically chosen by Simics unless it is provided as an argument to the command:

When a link component has been created, it is possible to connect the network devices by running the connect command for each Ethernet port. For demonstration, we will use x86 machines from the QSP-x86 package. Start the simulation with the firststeps-multi.simics start script and run the following commands:

To find a connector which is not connected for ethernet_cable/hub/switch components the get-free-connector command can be used. This command returns the name of a free connector:

Together the get-free-connector and connect commands can be used to connect an Ethernet device to a free connector:

Now, when all of the components of the system are configured and connected together, instantiate the link components:

It is also possible to create instantiated links with the new-ethernet-cable/hub/switch commands, but note that this only works if there is already at least one instantiated top-level component in the simulation.