RSTP/RPVST/PVST

Question 1

In RSTP, when are TCN BPDUs not generated?

Answer 1

When an edge port moves into forwarding mode.

Question 2

In RSTP, what happens when an edge port receives a BPDU?

Answer 2

It loses its edge port status, and the switch generates a TCN BPDU.

Question 3

To run RSTP, ports must be ___.

Answer 3

Full duplex.

Question 4

What protocol is rapid spanning tree defined by?

Answer 4

802.1w

Question 5

What does rapid spanning tree use in place of blocked ports?

Answer 5

Alternate ports.

Question 6

What CST states are combined into the RSTP discarding state?

Answer 6

Disabled, blocking and listening.

Question 7

Describe the states that a RSTP port will progress through on the way to a forwarding state.

Answer 7

Discarding, learning, forwarding.

Question 8

What are the two main port types in RSTP?

Answer 8

Point-to-point and edge.

Question 9

RSTP edge ports are always running ___.

Answer 9

Port fast.

Question 10

In RSTP, topology changes don’t occur when a ___ port moves to forwarding mode.

Answer 10

Edge.

Question 11

In RSTP, TCN BPDUs are not sent out on ___.

Answer 11

Edge ports.

Question 12

In RSTP, what does a switch do when it receives a TCN BPDU?

Answer 12

Clears the MAC entries for all ports besides the receiving port, and forwards the BPDU out all non-edge designated ports.

Question 13

In contrast to CST, all switches in RSTP continuously generate and send ___.

Answer 13

BPDUs.

Question 14

In RSTP, the max age timer is not used. What’s used in it’s place?

Answer 14

BPDUs. If three BPDUs are missed (6 seconds) the link is considered down and the superior BPDU is forgotten.

Question 15

Describe the RSTP synchronization.

Answer 15

When a RSTP root election takes place, the superior BPDU is forwarded throughout the network and must be “agreed upon” by all switches. This takes place with the “proposal” (the superior BPDUs) and “agreements”. being sent in reply.

Question 16

In RSTP, for a switch to send agreements and become synched, all its ports must be ___ or ___.

Answer 16

Discarding or an edge port.

Question 17

When running the “show spanning vlan x” command, under interface type, what does P2p indicate?

Answer 17

The connected switch is running RSTP.

Question 18

RPVST is essentially RSTP with what added feature?

Answer 18

The per-vlan configuration from PVST+.

Question 19

Briefly define PVST+.

Answer 19

Per-VLAN spanning tree. Runs an instance of STP for each individual VLAN. CPU heavy.

Question 20

PVST requires the use of ___, while PVST+ does not.

Answer 20

ISL trunks.

Question 21

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?

Answer 21

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

Question 22

What happens on a Cisco switch that runs Cisco IOS when an RSTP-configured switch receives 802.1d BPDU?

Answer 22

802.1d does not understand RSTP BPDUs because they are different versions, but when a RSTP switch receives an 802.1d BPDU, it responds with an 802.1d BPDU and eventually the two switches run 802.1d to communicate.

Question 23

Deifne PVST+

Answer 23

A Cisco-proprietary STP implementation, created many years before IEEE 802.1s and 802.1w, that speeds convergence and allows for one STP instance for each VLAN.

Question 24

Define RPVST+

Answer 24

The combination of PVST+ and Rapid Spanning Tree. It provides subsecond convergence time and is compatible with PVST+ and MSTP.