RSTP/RPVST/PVST Flashcards
In RSTP, when are TCN BPDUs not generated?
When an edge port moves into forwarding mode.
In RSTP, what happens when an edge port receives a BPDU?
It loses its edge port status, and the switch generates a TCN BPDU.
To run RSTP, ports must be ___.
Full duplex.
What protocol is rapid spanning tree defined by?
802.1w
What does rapid spanning tree use in place of blocked ports?
Alternate ports.
What CST states are combined into the RSTP discarding state?
Disabled, blocking and listening.
Describe the states that a RSTP port will progress through on the way to a forwarding state.
Discarding, learning, forwarding.
What are the two main port types in RSTP?
Point-to-point and edge.
RSTP edge ports are always running ___.
Port fast.
In RSTP, topology changes don’t occur when a ___ port moves to forwarding mode.
Edge.
In RSTP, TCN BPDUs are not sent out on ___.
Edge ports.
In RSTP, what does a switch do when it receives a TCN BPDU?
Clears the MAC entries for all ports besides the receiving port, and forwards the BPDU out all non-edge designated ports.
In contrast to CST, all switches in RSTP continuously generate and send ___.
BPDUs.
In RSTP, the max age timer is not used. What’s used in it’s place?
BPDUs. If three BPDUs are missed (6 seconds) the link is considered down and the superior BPDU is forgotten.
Describe the RSTP synchronization.
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.
In RSTP, for a switch to send agreements and become synched, all its ports must be ___ or ___.
Discarding or an edge port.
When running the “show spanning vlan x” command, under interface type, what does P2p indicate?
The connected switch is running RSTP.
RPVST is essentially RSTP with what added feature?
The per-vlan configuration from PVST+.
Briefly define PVST+.
Per-VLAN spanning tree. Runs an instance of STP for each individual VLAN. CPU heavy.
PVST requires the use of ___, while PVST+ does not.
ISL trunks.
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?
The new switches are using RSTP instead of legacy IEEE 802.1D STP.
What happens on a Cisco switch that runs Cisco IOS when an RSTP-configured switch receives 802.1d BPDU?
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.
Deifne PVST+
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.
Define RPVST+
The combination of PVST+ and Rapid Spanning Tree. It provides subsecond convergence time and is compatible with PVST+ and MSTP.
