WalT network structure


The following figure describes the network architecture of a WALT platform in its simplest form.

          --------    --------
         |switch  |  |switch  |
          --------    --------
            | | |      | |  |
            | |  ------  |   -------
            | |          |          |
            | |   -----  |   -----  |   -----
            |  --|node1|  --|node2|  --|node3|
            |     -----      -----      -----
 '          |
 |walt-out  |walt-net
|WALT server                |

The WALT server is the brain of the platform. It stores the WALT images and exposes them to nodes over the network.

Nodes use a network booting procedure (TFTP + NFS) to boot the operating system contained in a selected WALT image.

walt-net and walt-out networks

As shown in the figure, there are two main requirements regarding network setup:

  • The server should have internet connectivity, in order to be able to communicate with the docker hub. In these documentation pages, this is sometimes refered as walt-out.

  • The platform LAN (or, sometimes, VLAN) MUST be fully dedicated to WALT. The WALT server will fully manage this platform network, by providing various network services, such as DHCP, NFS, TFTP, etc. We call this platform network walt-net in these documentation pages and in configuration files.

Of course we can cascade several switches to extend walt-net, as shown on the figure. Caution: connecting a walt node directly to the server (with no intermediate switch) will not work!

Isolating networks walt-net and walt-out allows better experiment reproducibility. Thus, in the default configuration, they are isolated one from each other. However, one can alter this configuration and allow a specific set of nodes to access internet. Check-out walt help show node-netsetup for more info.

walt-adm: optional admin network

If WALT is installed in a building and reuses an existing network infrastructure, there is usually a dedicated VLAN already in place for remote administration of switches.

Instead of allowing remote administration (i.e. SNMP requests, see below) from network walt-net, admins usually prefer to give the WALT server access to this dedicated admin network.

We call this optional network walt-adm in these documentation pages and in configuration files.

Configuring WalT

WalT networking configuration is responsible for defining walt-net and optionally walt-adm. walt-out is out of scope because the default OS configuration providing internet connectivity is fine.

This configuration is most easily modified by running walt-server-setup --edit-conf. Check-out walt help show server-network-config for more info.

It is possible to configure a virtual-only platform where walt-net is not linked to a physical network interface. In this case, it will not be possible to detect physical nodes, but users can still work with virtual nodes. Such a virtual-only platform can be reconfigured later to accept physical nodes by running walt-server-setup --edit-conf again.

Network switch remote administration features

When configured to do so, the WALT server may send SNMP queries to a given switch, for one of these purposes:

  • retrieve LLDP data (Link Layer Discovery Protocol), for network discovery

  • activate / deactivate PoE on one of the ports (for remotely hard-rebooting a walt node or saving power)

These requests are disabled by default. You can activate and configure them for a given switch using walt device config <switch> <parameter>... (see walt help show device-config).

Of course this is only possible if the switch provides related features. See walt help show optional-features for more info.

Note that if walt-adm is configured, WALT may send SNMP requests on both walt-net and walt-adm networks. To clarify, let’s consider WALT has been installed in a large building, and some wall plugs have been dedicated to the experimentation network (thus they are associated to walt-net). In order to perform a small experiment with a few nodes on your desk, you could connect a small switch to one of these wall plugs, and connect your nodes on it. In this case, WALT will have to use walt-net to reach this small switch, and walt-adm to reach the switch managing the wall plug.