Chapter 4

Question 1

BPDU guard

Answer 1

Prevents accidental connection of switching devices to portfast enabled ports - connecting switches to portfast-enabled ports can cause layer to loops

Question 2

BPDU filtering

Answer 2

restricts the switch from sending unnecessary BPDUs out access ports

Question 3

Root guard

Answer 3

Prevents switches connected on ports configured as access ports from becoming the root switch

Question 4

Loop guard

Answer 4

Prevents root ports and alternate ports from moving to forwarding state when they stop receiving BPDUs

Question 5

If a portfast enabled interface receives a BPDU what happens?

Answer 5

the interface goes into err-disable state

Question 6

If BPDU filtering is on an interface it is the same as…

Answer 6

disabling spanning tree

Question 7

Superior BPDU

Answer 7

are received on a root guard-enabled port the port moves to root-inconsistent STP state which is the same as the listening state

Question 8

UDLD

Answer 8

unidirectional link detection

Question 9

UDLD Normal Mode

Answer 9

changes the UDLD-enabled port to an undetermined state if it stops receiving UDLD messages from its directly connected neighbor

Question 10

UDLD Aggressve Mode (preferred)

Answer 10

When a port stops receiving UDLD packets, UDLD tries to re-establish the connection with the neighbor, after 8 failed tries the port state changes to err-disabled

Question 11

Flex Links

Answer 11

provides an alternative to STP

Question 12

Potential STP Problems

Answer 12

Duplex mismatch
Unidirectional link failure
Frame corruption
Resource errors
PortFast configuration error

Question 13

Duplex Mismatch

Answer 13

Point-to-point link one side is configured as full duplex and the other side is configured as half duplex

Question 14

Unidirectional Link Failure

Answer 14

frequent cause of bridge loops

Question 15

Frame Corruption

Answer 15

is generally a result of a duplex mismatch, bad cable, or incorrect cable length

Question 16

Resource Errors

Answer 16

STP is performed by the CPU this means that if the CPU of th bridge s over-utilized it might lack the resources to send out BPDUs this is however unlikly