This new OpenFlow message format provides a cleaner interface and greater
detail and control over ports. It is now possible to see what features
the switch's port is currently configured as having, what it's advertising,
and what it's capable of handling. It is also possible to return the
features advertised by the port's peer.
To report on link status and whether a port is administratively enabled or
disabled, the reference switches poll. This change uses the Linux kernel's
device notification system, so that polling isn't necessary.
Justin Pettit