Mod 5.1-5.2: Purpose and Operations of STP

Question 1

____ is a loop-prevention network protocol that allows for redundancy while creating a loop-free Layer 2 topology.

Answer 1

Spanning Tree Protocol (STP)

Question 2

____is the original IEEE MAC Bridging standard for STP.

Answer 2

IEEE 802.1D

Question 3

Issues with Redundant Switch Links:
____ provides multiple network services by eliminating the possibility of a single point of failure.

Answer 3

Path redundancy

Question 4

When multiple paths exist between two devices on an Ethernet network, and there is no spanning tree implementation on the switches, a____ occurs.

Answer 4

Layer 2 loop

Question 5

A Layer 2 loop can result in ___instability, link saturation, and ___ on switches and end-devices, resulting in the network becoming unusable.

Answer 5

MAC address table
high CPU utilization

Question 6

True or false
Unlike the Layer 3 protocols, IPv4 and IPv6, Layer 2 Ethernet does not include a mechanism to recognize and eliminate endlessly looping frames.

Answer 6

True
Both IPv4 and IPv6 include a mechanism that limits the number of times a Layer 3 networking device can retransmit a packet via TTL (time to live) which is decremented by routers or hop limit in ipv6

Question 7

____ was developed specifically as a loop prevention mechanism for Layer 2 Ethernet.

Answer 7

STP

Question 8

Without STP enabled, Layer 2 loops can form, causing broadcast, multicast and unknown unicast frames to ___.

Answer 8

loop endlessly

Question 9

An____ frame is when the switch does not have the destination MAC address in its MAC address table and must forward the frame out all ports, except the ingress port.

Answer 9

unknown unicast

Question 10

A ____is an abnormally high number of broadcasts overwhelming the network during a specific amount of time.

Answer 10

broadcast storm

Question 11

Broadcast storms can be caused by a hardware problem such as a___ or from a___ in the network.

Answer 11

faulty NIC
Layer 2 loop

Question 12

SPANNING TREE ALGORITHM:
STP is based on an algorithm invented by ____while working for Digital Equipment Corporation, and published in the 1985 paper “An Algorithm for Distributed Computation of a Spanning Tree in an Extended LAN.”

Answer 12

Radia Perlman

Question 13

Radia Perlman’s ____ creates a loop-free topology by selecting a single root bridge where all other switches determine a single least-cost path.

Answer 13

spanning tree algorithm (STA)

Question 14

STA PROCESS:
Step 1:STP prevents loops from occurring by configuring a loop-free path through the network using strategically placed ____” ports

Answer 14

“blocking-state

Question 15

STA PROCESS:
Step 1: The switches running STP are able to compensate for failures by ___ the previously blocked ports and permitting traffic to traverse the alternate paths.

Answer 15

dynamically unblocking

Question 16

STA
Step 2: The spanning tree algorithm begins by selecting a ___

Answer 16

single root bridge

Question 17

Note: The STA and STP refers to ___ as bridges

Answer 17

switches

Question 18

STA
Step 3: STP ensures that there is only one logical path between all destinations on the network by intentionally ____ that could cause a loop

Answer 18

blocking redundant paths

Question 19

STA
Step 4: A blocked port has the effect of making that link a non-forwarding link between the two switches. Thus, this creates a ___ topology.

Answer 19

Loop-Free

Question 20

STA
Step 5: The physical paths still exist to provide redundancy, but these paths are disabled to prevent the loops from occurring. If the path is ever needed to compensate for a network cable or switch failure, STP ___ the paths and unblocks the necessary ports to allow the redundant path to become active.

Answer 20

recalculates

Question 21

True or false
STP recalculation happens only during link failure.

Answer 21

False
STP recalculations can also occur any time a new switch or new inter-switch link is added to the network.

Question 22

Reorder the following:
Steps to a Loop-Free Topology

Elect Alternate (blocked) ports
Elect root ports
Elect root bridge
Elect designated ports

Answer 22

Elect the root bridge.
Elect the root ports.
Elect designated ports.
Elect alternate (blocked) ports.

Question 23

During STA and STP functions, switches use ___ to share information about themselves and their connections.

Answer 23

Bridge Protocol Data Units (BPDUs)

Question 24

BPDUs are used to elect the___.

Answer 24

root bridge, root ports, designated ports, and alternate ports

Question 25

Each BPDU contains a ___ that identifies which switch sent the BPDU.

Answer 25

bridge ID (BID)

Question 26

The ___is involved in making many of the STA decisions including root bridge and port roles.

Answer 26

BID

Question 27

The lowest BID value is determined by the combination of these three fields:

Answer 27

bridge priority value, an extended system ID, and the MAC address of the switch

Question 28

Bridge Priority has ___ bits

Answer 28

4

Question 29

Extended System Id has __ bits

Answer 29

12

Question 30

MAC address has __ bits

Answer 30

48

Question 31

Bridge priority: The default priority value for all Cisco switches is the decimal value ___.

Answer 31

32768

Question 32

Bridge Priority: The range is 0 to 61440 in increments of ___

Answer 32

4096

Question 33

True or false. higher bridge priority is preferable because the highest value takes precedence.

Answer 33

False A lower bridge priority is preferable. A bridge priority of 0 takes precedence over all other bridge priorities

Question 34

The ___value is a decimal value added to the bridge priority value in the BID to identify the VLAN for this BPDU.

Answer 34

extended system ID

Question 35

The extended system ID allows later implementations of STP to have different ___ for different sets of VLANs

Answer 35

root bridges

Question 35

The extended system ID allows later implementations of STP to have different ___ for different sets of VLANs

Answer 35

root bridges

Question 36

When two switches are configured with the same priority and have the same extended system ID, the switch having the ____ with the lowest value, expressed in hexadecimal, will have the lower BID.

Answer 36

MAC address

Question 37

1. Elect the Root bridge True or false The STA designates multiple switch as the root bridge and uses it as the reference point for all path calculations.

Answer 37

False Should be single

Question 38

1. Elect the Root bridge True or false All switches in the broadcast domain participate in the election process.

Answer 38

True After a switch boots, it begins to send out BPDU frames every two seconds.

Question 39

The BPDU frames sent by switches contain the BID of the sending switch and the BID of the root bridge, known as the ___.

Answer 39

Root ID

Question 40

The switch with the ___ BID will become the root bridge.

Answer 40

lowest

Question 41

Is it possible for two or more switches to have the same priority?

Answer 41

yes, because the default BID is 32768

Question 42

In this scenario, where the priorities are the same, the switch with the ___ will become the root bridge.

Answer 42

lowest MAC address

Question 43

When the root bridge has been elected for a given spanning tree instance, the STA starts the process of determining the___ to the root bridge from all destinations in the broadcast domain.

Answer 43

best paths

Question 44

The path information, known as the ___, is determined by the sum of all the individual port costs along the path from the switch to the root bridge.

Answer 44

internal root path cost

Question 45

The default port costs are defined by the___.

Answer 45

speed at which the port operates

Question 46

Link Speed STP Cost RSTP Cost 10 Gbps---------2 ____________- _________________4 -----------20,000 100 Mpbs ______________ __________ _______________ 1000__________________

Answer 46

10 Gbps 2 2,000 1 Gbps 4 20,000 100 Mbps 19 200,000 10 Mbps 100 2,000,000

Question 47

Are port cost configurable?

Answer 47

Yes. The ability to configure individual port costs gives the administrator the flexibility to manually control the spanning tree paths to the root bridge.

Question 48

2. Elect the Root Ports Every non-root switch will select how many root ports?

Answer 48

Only one

Question 49

The___ is the port closest to the root bridge in terms of overall cost (best path) to the root bridge

Answer 49

root port

Question 50

Paths with the ___ cost become preferred, and all other redundant paths are blocked.

Answer 50

lowest

Question 51

3. Elect Designated Ports Every segment between two switches will have how many designated ports?

Answer 51

one

Question 52

The ____ is a port on the segment (with two switches) that has the internal root path cost to the root bridge

Answer 52

designated port

Question 53

True or false The root port has the best path to receive traffic leading to the root bridge.

Answer 53

False. It should be designated port

Question 54

What happens to ports that are not a designated port nor root port?

Answer 54

It becomes an alternate or blocked port.

Question 55

3. Elect Designated Ports All ports on the ___ are designated port

Answer 55

root bridge

Question 56

3. Elect Designated Ports If one end of a segment is a root port, then the other end is a ___

Answer 56

designated port.

Question 57

3. Elect Designated Ports In this case, the port on the switch with the____path to the root bridge is the designated port for the segment

Answer 57

least-cost

Question 58

4. Elect Alternate (Blocked) Ports If a port is not a root port or a designated port, then it becomes an alternate (or ____) port.

Answer 58

backup

Question 59

4. Elect Alternate (Blocked) Ports Alternate ports and backup ports are in __ or ___ state to prevent loops.

Answer 59

discarding blocking

Question 60

When a switch has multiple equal-cost paths to the root bridge, the switch will determine a port using the following criteria:

Answer 60

Lowest sender BID Lowest sender port priority Lowest sender port ID

Question 61

STP TIMERS: The ** is the interval between BPDUs. The default is 2 seconds but can be modified to between 1 and 10 seconds.

Answer 61

Hello timer *Hello time*

Question 62

STP TIMERS The ** is the time that is spent in the listening and learning state. The default is 15 seconds but can be modified to between 4 and 30 seconds.

Answer 62

Forward Delay Timer *forward delay*

Question 62

STP TIMERS The ** is the time that is spent in the listening and learning state. The default is 15 seconds but can be modified to between 4 and 30 seconds.

Answer 62

Forward Delay Timer *forward delay*

Question 63

STP TIMER The ** is the maximum length of time that a switch waits before attempting to change the STP topology. The default is 20 seconds but be modified to between 6 and 40 seconds.

Answer 63

Max Age Timer *Max age*

Question 64

PORT STATE The port is an alternate port and does not participate in frame forwarding.

Answer 64

Blocking The port receives BPDU frames to determine the location and root ID of the root bridge. BPDU frames also determine which port roles each switch port should assume in the final active STP topology. With a Max Age timer of 20 seconds, a switch port that has not received an expected BPDU from a neighbor switch will go into the blocking state.

Question 65

PORT STATE After the blocking state, a port will move to the __.

Answer 65

listening state The port receives BPDUs to determine the path to the root. The switch port also transmits its own BPDU frames and informs adjacent switches that the switch port is preparing to participate in the active topology.

Question 66

PORT STATE A switch port transitions to the ____ after the listening state.

Answer 66

Learning During the learning state, the switch port receives and processes BPDUs and prepares to participate in frame forwarding. It also begins to populate the MAC address table. However, in the learning state, user frames are not forwarded to the destination.

Question 67

PORT STATE In the ___ state, a switch port is considered part of the active topology.

Answer 67

forwarding

Question 68

PORT STATE A switch port in the ___ does not participate in spanning tree and does not forward frames.

Answer 68

disabled state

Question 69

Operational details of each port state Port State |BPDU | MAC Table |Forwarding Data Frames? Blocking |Receive _____ No

Answer 69

No update

Question 70

Operational details of each port state Port State | BPDU |MAC Table| Forwarding Data Frames? Listening _____ _____ No

Answer 70

Receive and send No update

Question 70

Operational details of each port state Port State |BPDU | MAC Table |Forwarding Data Frames? Listening _____ _____ No

Answer 70

Receive and send No update

Question 71

Operational details of each port state Port State | BPDU | MAC Table |Forwarding Data Frames? Learning ______ _____ No

Answer 71

Receive and Send Updating Table

Question 72

Operational details of each port state Port State | BPDU | MAC Table | Forwarding Data Frames? Forwarding Receive and send _____ ___

Answer 72

Updating table Yes

Question 73

Operational details of each port state Port State | BPDU | MAC Table | Forwarding Data Frames? ______ none sent or received | No Update _____

Answer 73

Disabled No

Question 74

True or false STP can only be configured to operate in an environment with only one VLANs

Answer 74

False In Per-VLAN Spanning Tree (PVST) versions of STP, there is a root bridge elected for each spanning tree instance. This makes it possible to have different root bridges for different sets of VLANs.