STP

Question 1

Layer 2 loop issues

Answer 1

MAC database instability
Broadcast storms
Multiple frame transmission

Question 2

MAC Database Instability

changes in the MAC address table, a switch do not know which port to forward frames

Answer 2

MAC Database Instability

Question 3

So many broadcast frames in a layer 2 loop that use all available bandwidth and make the network unreachable for legitimate network traffic

Answer 3

Broadcast storms

Question 4

Causes of broadcasts storms

Answer 4

Denial of Service (DoS)

Can develop in seconds and bring the network down

Question 5

A switch does not have the destination MAC address in its MAC address table and has to broadcast the frame out all ports except the port the frame was received on

Answer 5

Duplicate Unicast Frames

Question 6

Blocks redundant paths that could cause a loop

Answer 6

Spanning Tree protocol

Question 7

Used to prevent loop and duplication of data frames in the ethernet network

Answer 7

STP

Question 8

Lowest Bridge ID (BID)

Bridge priority and MAC Address

Answer 8

Root Bridge

Question 9

Port Roles

selected on a per-segment (each link) basis, based on the cost to get to root bridge or either side of this link

Answer 9

Designated Port

Question 10

Port roles

one port on a switch that has the lowest cost to reach the root bridge

Answer 10

Root Port

Question 11

Port Roles ( RSTP only)
Backup port for the root port

Answer 11

Backup root

Question 12

Port Roles (RSTP only)
Backup port for the designated port when the other side is not a root port

Answer 12

Alternate port

Question 13

Cisco update 802.1D; each VLAN has its own spanning-tree instance

Answer 13

PVST+

Question 14

Cisco enhancement of RSTP using PVST+

Answer 14

Rapid PVST+

Question 15

Disadvantages of Original 802.1D

Answer 15

No load sharing
Low CPU utilization
One uplink must block for all VLANs

Question 16

Advantages of Cisco PVST+

Answer 16

Can load balance
One port can be blocking for one VLAN and forwarding for another VLAN
Can stress the CPU if a large number of VLANs are used

Question 17

Port States in STP (802.1D)

Answer 17

Disabled 
Blocking 
Listening 
Learning 
Forwarding

Question 18

Port States in Rapid STP (802.1w)

Answer 18

Discarding
Learning
Forwarding

Question 19

Port Roles in STP (802.1D)

Answer 19

Root (Forwarding)
Designated (Forwarding)
Non-designated (Blocking)

Question 20

Port Roles in Rapid STP (802.1w)

Answer 20

Root (Forwarding)
Designated (Forwarding)
Alternate (Discarding) Backup (Discarding)

Question 21

BPDUs are used as a keepalive mechanism

Answer 21

RSTP BPDUs

Question 22

A port that immediately goes to forwarding state,

has an end device connected - NEVER another switch

Answer 22

Edge Ports

Question 23

Edge Ports

Answer 23

Uses the spanning-tree portfast command

Question 24

Link Types

Answer 24

Shared- A point in half -duplex mode connecting a hub to a switch

Question 25

2 ways to influence the root bridge election process

Answer 25

spanning-tree vlan x root primary/secondary Change Priority spanning-tree vlan x priority x

Question 26

What does the portfast command do?

Answer 26

Used on end devices attached. Put a port in a forwarding state Allows DHCP to work properly

Question 27

What does BPDU Guard do?

Answer 27

Disables a port that has PortFast configured on it if a BPDU is received

Question 28

Issues that result a broadcast storm

Answer 28

Due to high processing demands during a broadcast storm, communication may fail between end stations in the broadcast domain. During a broadcast storm, constant changes to the MAC address table prevent a switch from accurately forwarding frames.

Question 29

What is the first step of the spanning-tree election process? ( After Rebooting)

Answer 29

All the switches send out BPDUs advertising themselves as the root bridge.

Question 30

When PVST is running over a switched network, which port state can participate in BPDU frame forwarding based on BPDUs received, but does not forward data frames?

Answer 30

Listening

Question 31

What is one way to correct a spanning tree failure?

Answer 31

Manually remove redundant links in the switched network.

Question 32

a protocol that allows multiple VLANs to run in a single spanning-tree instance, Rapid PVST+

Answer 32

MSTP

Question 33

Which port state will switch ports immediately transition to when configured for PortFast?

Answer 33

Forwarding

Question 34

What additional information is contained in the 12-bit extended system ID of a BPDU?

Answer 34

VLAN ID