altn, bkup, rapid-...

it is paramount to note that rapid-pvst+ not only defined a discarding port role to replace the ineffective blocking and listening port states from 802.1d (pvst+ for  cisco indoctrinates) but also the port roles of alt and bkup...

altn is simply an alternate root port on a non root switch that will take over in case of root port failure...

backup is the same idea for the dp of a segment...

this is an important distinction which allows for quick replacement in case of failure...

it's also worth noting that the fast's are built into the protocol (portfast, backbonefast and uplinkfast)

this was actually a segue to this seemingly silly command:

spanning-tree link-type point-to-point

what the hell is that?

by definition a full duplex port is point-to-point, and when would you ever need to declare something that is already declared by default... when connecting to a shared (half duplex port) or mst port perhaps...

here are some thoughts on this, er, thing:

http://cciepursuit.wordpress.com/2008/03/07/spanning-tree-link-type/ 

i find it very interesting that wendell and company blast through this in:

CCIE Routing and Switching
Certification Guide
Fourth Edition

Configuring RPVST+ is straightforward. In global configuration mode, issue the spanning-tree mode rapid-pvst command. Then, optionally, on an interface (VLAN, physical, or PortChannel), configure the spanning-tree link-type point-to-point command. This configures the port for fast changeover to the forwarding state.

this leads me to believe that the ccie cert guide v4 bears meticulous viewing for such loaded weapons...