STP Port States and Roles 2 — Questions and Answers
Question 1: Which STP port role is assigned to the port that provides the best path from a non-root switch to the root bridge?
- Designated Port
- Root Port (Correct answer)
- Alternate Port
- Backup Port
Correct answer: Root Port
Each non-root switch has exactly one Root Port, which is the port offering the lowest-cost path toward the root bridge.
Question 2: On each network segment, which STP port role is responsible for forwarding traffic toward the root bridge on behalf of that segment?
- Root Port
- Designated Port (Correct answer)
- Non-Designated Port
- Backup Port
Correct answer: Designated Port
The Designated Port on each segment is the one elected to forward traffic from that segment toward the root bridge.
Question 3: In RSTP (802.1w), what is the name of the port role that provides an alternate path to the root bridge and can quickly take over if the Root Port fails?
- Backup Port
- Designated Port
- Alternate Port (Correct answer)
- Edge Port
Correct answer: Alternate Port
The Alternate Port in RSTP is a blocking port that offers a redundant path to the root bridge and can rapidly transition to Root Port if needed.
Question 4: What port role does the root bridge assign to ALL of its active ports?
- Root Port
- Designated Port (Correct answer)
- Alternate Port
- Blocked Port
Correct answer: Designated Port
All active ports on the root bridge are Designated Ports because the root bridge always has the best path cost (zero) to itself.
Question 5: In RSTP, which port role is in Discarding state and provides a backup to a Designated Port on the SAME switch segment?
- Alternate Port
- Backup Port (Correct answer)
- Root Port
- Edge Port
Correct answer: Backup Port
A Backup Port is an RSTP port role that provides redundancy for a Designated Port on the same shared segment, but it stays in Discarding state.
Question 6: How is the Root Port selected when two ports on the same switch have equal path costs to the root bridge?
- By the highest port priority
- By the lowest port priority then lowest port ID (Correct answer)
- By the highest MAC address
- By the longest uptime
Correct answer: By the lowest port priority then lowest port ID
When path costs are tied, STP uses the lowest sender Bridge ID, then lowest port priority, and finally lowest port ID (number) as tiebreakers.
Question 7: A port that is administratively shut down in STP is in which port state?
- Blocking
- Listening
- Discarding
- Disabled (Correct answer)
Correct answer: Disabled
The Disabled state applies to ports that have been administratively shut down and do not participate in STP at all.
STP Port States and Roles 2
Which STP port role is assigned to the port that provides the best path from a non-root switch to the root bridge?