CCNA: (SRWE) - STP and RSTP Modification

Match the following

• Designated

• Forwards traffic from a segment to the root bridge.

• Root

• Discarding state that quickly transitions to forwarding if needed.

• Backup

• Forwards traffic to the root bridge.

• Alternative

• Immediately transitions to a forwarding port if an error occurs with the current forwarding port.

What is the main benefit of RSTP over STP?

• RSTP achieves faster convergence than STP.

• BPDUs are only initiated by the root bridge in RSTP, whereas in STP all switches initiate BPDUs.

• RSTP has less port roles than STP.

• RSTP has more port states than STP.

Answer explanation

RSTP can achieve much faster convergence than STP in a properly configured network, sometimes in as little as a few hundred milliseconds. All switches in an RSTP network send BPDUs as a "keepalive" mechanism. RSTP has fewer port states but more port roles making it leaner and quicker to converge and reconverge after issues. RSTP minimizes downtime and ensures efficient data transmission.

A port on an RSTP switch is not forwarding frames, is blocked to prevent loops but is still able to listen to BPDUs to learn the network topology.  What type of port state is being described?

• Disabled

• Learning

• Listening

• Discarding

Answer explanation

In RSTP, a port that is in the discarding state is blocked to prevent loops, does not forward frames, and listens to BPDUs to learn the topology.

What does RSTP use to select the root bridge?

• The switch with the highest BID.

• The switch with the lowest MAC address.

• The switch with the highest extended system ID.

• The switch with the lowest BID.

Answer explanation

RSTP selects the root bridge based on the lowest bridge ID. The bridge ID is a combination of the bridge priority (i.e., 32,768), the MAC address of the bridge and the VLAN ID.

In RSTP, a switch with four interfaces that connects to other RSTP switches, has been selected as the root bridge. What port type will be associated with the root bridge interfaces?

• some will be root ports and some of them will be alternate ports

• all will be designated ports

• all will be alternate ports

• all will be root ports

Answer explanation

Since the switch is the root bridge, it does not need root ports. Therefore, all ports on a root bridge that are connected to other STP switches are designated ports.

A network administrator configures PortFast on access ports that are connected to end devices. What does the configuration accomplish?

• The access ports are temporarily put into a loop-inconsistent state.

• It prevents the forwarding of BPDUs to and from those access ports.

• It ensures that an unauthorized switch cannot connect to those access ports.

• The access ports will transition directly to the forwarding state.

Answer explanation

The PortFast feature enables access ports connecting to end devices to transition directly to the forwarding state, thereby bypassing the listening and learning states.

Match the RSTP term with the description

• Loop Guard

• Monitors BPDUs and puts port into an inconsistent state if BPDUs stop on port.

• Root Guard

• Ensures that no unauthorized switches can become the root bridge.

• BPDU Filter

• Prevents unauthorized switched or devices from introducing loops in the network.

• Bridge Assurance

• Transitions ports to blocking state if no BPDUs are received on designated ports in a certain period.

• BPDU Guard

• Controls the propagation of BPDU packets into or out of a port.

What happens if a BPDU is received on a port that has BPDU Guard configured?

• The BPDU is sent to the closest root port.

• The BPDU is ignored

• The BPDU is returned to the sender.

• The port is disabled.

Answer explanation

If a BPDU Guard-enabled port receives a BPDU, it triggers a security mechanism that puts the port into an error-disabled state and immediately disables (shuts down) the port.

Which two statements are correct concerning RSTP features? (Choose two.)

• BPDU Guard and BPDU Filter should not be configured on the same port.

• PortFast and Root Guard must be configured on the same port.

• Only one RSTP feature should be configured on a port at the same time.

• Loop Guard and Root Guard should be configured on the same port

• PortFast should be configured on an interface that is configured as a trunk.

Answer explanation

BPDU Guard and BPDU Filter: Do not configure a port with both commands since enabling both on the same interface effectively cancels the BPDU Guard feature.
Loop Guard and Root Guard should be configured together. While Root Guard protects against unauthorized switches attempting to become the root bridge, Loop Guard protects against unintended loops caused by link failures.

Where is the best place to configure BPDU filtering?

• on all root and trunking ports

• on designated ports that connect to other switches

• on all ports within the network

• on access ports that connect to end devices

Answer explanation

BPDU Filter is best configured on access ports connecting to end devices to avoid unnecessary BPDU processing.