Which spanning-tree technology is used to accomplish backup root port selection?

Pilot testing of the new switching infrastructure finds that when the root port is lost, STP immediately replaces the root port with an alternative root port.

Which spanning-tree technology is used to accomplish backup root port selection?
A . PVST+
B . PortFast
C . BackboneFast
D . UplinkFast
E . Loop Guard
F . UDLD

View Answer

Answer: D

Explanation:

If a switch loses connectivity, it begins using the alternate paths as soon as the spanning tree selects a new root port. By enabling UplinkFast with the spanning-tree uplinkfast global configuration command, you can accelerate the choice of a new root port when a link or switch fails or when the spanning tree reconfigures itself. The root port transitions to the forwarding state immediately without going through the listening and learning states, as it would with the normal spanning-tree procedures. UplinkFast provides fast convergence after a direct link failure and achieves load balancing between redundant Layer 2 links using uplink groups. An uplink group is a set of Layer 2 interfaces (per VLAN), only one of which is forwarding at any given time. Specifically, an uplink group consists of the root port (which is forwarding) and a set of blocked ports, except for self-looping ports. The uplink group provides an alternate path in case the currently forwarding link fails. Reference: http://www.cisco.com/c/en/us/td/docs/switches/lan/ catalyst2960/software/release/12- 2_55_se/configuration/guide/scg_2960/swstpopt.html