Optional features of a WalT platform¶
Depending on the network switches and their configuration, WalT may provide the following valuable features.
Preliminary note about SNMP¶
SNMP is the Simple Network Management Protocol. It allows to automate remote administration tasks on a network equipment. Most professional grade switches handle this protocol. The following optional features of WalT are not available otherwise.
Automated discovery of the network topology¶
LLDP is the Link Layer Discovery Protocol. It allows a network equipment
to know the list of its immediate (i.e., at mac layer) neighbors. If a
network switch of the WalT network has this feature and accepts remote
SNMP queries from the WalT server, then the WalT server can get the list
of devices connected on it. When configured to do so (see below), the
WalT server can query all switches (command walt device rescan
) and
then display a whole tree of the WalT network (command
walt device tree
).
PoE for simplified deployment, hard-reboots and power savings¶
PoE for simplified deployment¶
PoE means Power over Ethernet. It consists of using the same ethernet cable for bringing both power and data to a device.
PoE corresponds to a standard protocol, named 802.3af (or 802.3at for PoE+) which the devices at both ends must comply with. Thus, in the case of WalT, we recommend to buy PoE compliant switches, and to power the nodes with PoE when possible. For instance, raspberry pi boards 3B+ and 4B can be powered by a “PoE HAT” designed by the raspberry pi foundation. Other boards can rely on an external PoE splitter.
Having one cable per node instead of two obviously simplifies platform deployment. If a switch provides SNMP, LLDP and PoE features, WalT also implements the more interesting features described below.
PoE hard-reboots¶
If a PoE-powered node is stuck for some reason (the experiment code
introduced a bug in the Linux kernel, a temporary firmware or network
issue occured, etc.), the WalT server may be able to power-cycle it
remotely, to force a reboot. The command walt node reboot <node>
actually tries a standard reboot request first, and if the node does not
reply, it will automatically run this hard-reboot operation if
available. The power-cycle operation is implemented by sending a request
to the switch to stop powering the port where the node is connected.
After one second, another request is sent to recover the powering.
Note: the switch must support PoE (obviously), SNMP (for remote requests) and LLDP (to know on which port the node is connected).
PoE power saving¶
When a PoE-powered WalT node has not been used for 2 hours, WalT will
automatically disable PoE on the corresponding switch port to save
power. The concept of “unused node” is rather conservative: only free
nodes (cf. walt help show node-ownership)
are considered unused after 2 hours. Thus, thanks to commands
walt node acquire
and walt node release
, experiments involving
unattended nodes and lasting more than 2 hours cannot be interrupted by
this power saving feature.
Again, this requires that the switch supports PoE (obviously), SNMP (for remote requests) and LLDP (to know on which port the node is connected).
Activating these optional features in WalT¶
In some complex environments, remote administration of a given switch by WalT may not be allowed; or LLDP/PoE may not be available. Thus, these features are disabled by default. As a result, WALT must be explicitely allowed to use these features on a given switch, by using walt device config.