After the recent upgrade of the switching infrastructure, the network engineer notices that the port roles that were once "blocking" are now defined as "alternate" and "backup." What is the reason for this change?

A. The new switches are using RSTP instead of legacy IEEE 802.1D STP.

B. IEEE 802.1D STP and PortFast have been configured by default on all newly implemented Cisco Catalyst switches.

C. The administrator has defined the switch as the root in the STP domain.

D. The port roles have been adjusted based on the interface bandwidth and timers of the new Cisco Catalyst switches.








 

Suggested Answer: A

RSTP works by adding an alternative port and a backup port compared to STP. These ports are allowed to immediately enter the forwarding state rather than passively wait for the network to converge.
RSTP bridge port roles:
* Root port  A forwarding port that is the closest to the root bridge in terms of path cost
* Designated port  A forwarding port for every LAN segment
* Alternate port  A best alternate path to the root bridge. This path is different than using the root port. The alternative port moves to the forwarding state if there is a failure on the designated port for the segment.
* Backup port  A backup/redundant path to a segment where another bridge port already connects. The backup port applies only when a single switch has two links to the same segment (collision domain). To have two links to the same collision domain, the switch must be attached to a hub.
* Disabled port  Not strictly part of STP, a network administrator can manually disable a port
Reference: http://www.cisco.com/c/en/us/support/docs/lan-switching/spanning-tree-protocol/24062-146.html

This question is in 300-115 Implementing Cisco IP Switched Networks (SWITCH) Exam
For getting Cisco Certified Network Professional (CCNP) Routing and Switching Certificate





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