Planetlab Ping-of-Death (POD)
-----------------------------
The Planetlab POD is a Linux kernel patch that creates the feature
of resetting and rebooting a computer when a particularily
formatted ICMP "ping" commmand is received.

A PlanetLab node's kernel gets a host, mask and hash value through
sysctl's that are performed on the node.  The node then looks
for an ICMP packet from a host matching the host/mask and, if the
packet payload is the hash value, the node forces an immediate
reboot.

From a controlling host's side, one invokes commands on the
remote node to set the host, mask and hash values and remembering
the hash value.  When the rebooting of a remote node is required,
the remembered hash value is looked up and sent to the node
in a specially constructed ICMP packet.

This POD system uses the same packet definition as EMULAB and uses
the some code from EMULAB to generate and transmit the packet.
No reason to invent something new.

Contolling host tools:
pod.py    Used to send both ICMP and UDP based POD packets. Requires
          the hostname to send the packet do, and the configured
          hash/key for the specified node.