Chapter 15 - Enhanced Switching Technologies

Question 1

_____ _____ _____ achieves it’s primary objective of preventing network loops on layer 2 network bridges by monitoring the network to track all links and shut down redundant ones.

Answer 1

Spanning Tree Protocol (STP)

Question 2

STP uses the _____ _____ _____ to first create a topology database and then search out and disable redundant links. \

Answer 2

Spanning Tree Algorithm (STA)

Question 3

With STP running, frames will be forwarded on only _____, _____-_____ links.

Answer 3

premium, STP-chosen

Question 4

The _____ _____ is the bridge with the lowest and, therefore, the best bridge ID.

Answer 4

Root Bridge

Question 5

The switches within an STP network _____ a root bridge.

Answer 5

elect

Question 6

Once the root bridge has been elected, all other bridges must create a _____ path to it.

Answer 6

single

Question 7

the port with the best path to the root bridge is called the _____ _____.

Answer 7

Root Port

Question 8

_____-_____ _____ exchange BPDUs with all the other bridges and update the STP topology database on all switches. This prevents loops and helps to defend against link failures.

Answer 8

Non-Root Bridges

Question 9

Each switch compares the parameters in the _____ _____ _____ _____ that it send to a neighbor with the parameters in the _____ _____ _____ _____ that it receives from other neighbors.

Answer 9

Bridge Protocol Data Unit (BPDU)

Question 10

Inside the BPDU is the _____ _____.

Answer 10

Bridge ID

Question 11

The _____ _____ is how STP keeps track of all of the switches on the network.

Answer 11

Bridge ID

Question 12

The bridge ID is determined by a combination of the _____ _____, which is 32,768 by default on all Cisco switches, and the _____ _____ _____.

Answer 12

bridge priority, base MAC address

Question 13

Most networks benefit by forcing a specific bridge or switch to be the root bridge by setting it’s _____ _____ lower than the default value.

Answer 13

bridge priority

Question 14

_____ _____ determines the best path when multiple links are used between 2 switches.

Answer 14

Port Cost

Question 15

the cost of a link is determined by the _____ of a link.

Answer 15

bandwidth

Question 16

_____ _____ is calculated for each unique path by adding the individual port costs encountered on the way to the root bridge.

Answer 16

Path Cost

Question 17

STP uses _____ to determine how a port on a switch will act within the spanning-tree algorithm.

Answer 17

Roles

Question 18

The _____ _____ is the link with the lowerst path cost to the root bridge.

Answer 18

Root Port

Question 19

When multiple links connect to the same device, the port connected to the _____ _____ _____ on the upstream switch will be the one that’s used.

Answer 19

lowest port number

Question 20

The root bridge can never have a _____ _____ designation, while ever other switch in a network must have one.

Answer 20

Root Port

Question 21

A _____ _____ is one that’s been determined to have the best (lowest) cost to get to on a given network segment, compared to other ports on that segment.

Answer 21

Designated Port

Question 22

A designated port will be marked as a _____ _____.

Answer 22

Forwarding Port

Question 23

You can only have _____ forwarding port per network segment.

Answer 23

one

Question 24

_____ _____ ports are basically the ones left over after the root ports and designated ports have been determined.

Answer 24

Non-Designated

Question 25

Non-designated ports are put into _____ or _____ discarding mode - they DO NOT forward frames.

Answer 25

blocking, discarding

Question 26

A _____ _____ forwards frames and will be either a root port or a designated port.

Answer 26

Forwarding Port

Question 27

While it will never forward frames in order to prevent loops, a _____ _____ will still always listen to the BPDU frames from neighbor switches and will drop any and all other frames received.

Answer 27

Blocked Port (this term is specific to 801.d)

Question 28

This is the term used with 802.1w and is analogous to the term "blocking port" used with 802.1d.

Answer 28

Alternate Port or Backup Port

Question 29

The ports on a bridge or switch running IEEE 802.1d STP can transition through _____ different states.

Answer 29

5

Question 30

A port in the _____ _____ state doesn't participate in frame forwarding or STP.

Answer 30

administratively disabled

Question 31

The purpose of the _____ state is to prevent the use of looped paths. All ports are in the _____ state by default when the switch is powered up.

Answer 31

Blocking

Question 32

A port in the _____ state listens to BPDUs to make sure no loops occur on the network before passing data frames. It prepares to forward data frames without populating the MAC address table.

Answer 32

Listening

Question 33

A port in _____ state listens to BPDUs and learns all paths in the switched network. It populates the MAC address table but still doesn't forward data frames.

Answer 33

Learning

Question 34

_____ _____ refers to the time it takes to transition a port from listening to learning mode, or from learning to forwarding mode.

Answer 34

Forward Delay

Question 35

What is the length of the Forward Delay set to be default on Cisco switches, and the output of which command shows this setting.

Answer 35

15 seconds, show spanning-tree

Question 36

If a port is still a designated or root port at the end of the learning state, it will enter the _____ state.

Answer 36

Forwarding

Question 37

Switch ports are most often in either the _____ or _____ state.

Answer 37

blocking, forwarding

Question 38

Once a switch determines the best patj to the root bridge for it's root port and any designated ports, and other redundant ports will be in _____ mode.

Answer 38

Blocking

Question 39

If a switch determines that a blocked port should become the designated or root port because of a topology change, it will go into _____ mode and check all BPDUs it receives to make sure it won't create a loop once the port moves into forwarding mode.

Answer 39

Listening

Question 40

_____ occurs when all ports on bridges and switches have transitioned to either forwarding or blocking modes. No data will be forwarded until _____ is complete. _____ is vital because it ensures that all devices have a coherent database.

Answer 40

Convergence

Question 41

What is the port cost for a 10 Mb/s link?

Answer 41

100

Question 42

What is the port cost for a 100 Mb/s link?

Answer 42

19

Question 43

What is the port cost for a 1000 Mb/s link?

Answer 43

4

Question 44

What is the port cost for a for a 10,000 Mb/s link?

Answer 44

2

Question 45

Every port on the _____ _____ is a designated, or forwarding, port for a segment.

Answer 45

Root Bridge

Question 46

The bridge ID is _____ bytes long and includes both the priority and the MAC address of the device.

Answer 46

8

Question 47

If 2 bridges or switches happen to have the same priority value, the _____ _____ becomes the tiebreaker for figuring out which one has the lowest bridge ID.

Answer 47

MAC address

Question 48

Prior to the election of the root bridge, BPDUs are sent every _____ seconds out all active ports on a bridge/switch by default, and they're received and processed by all bridges.

Answer 48

2

Question 49

_____ _____ is the original standard for bridging and STP, which is really slow but requires very little bridge resources.

Answer 49

IEEE 802.1d

Question 50

IEEE 802.1d is also referred to as _____ _____ _____.

Answer 50

Common Spanning Tree (CST)

Question 51

_____ is the Cisco proprietary enhancement for STP that provides a separate 802.1d spanning-tree instance for each VLAN. While it is just as slow as the CST protocol, it also provides more than one root bridge and uses more resources than CST.

Answer 51

PVST+

Question 52

_____ _____ or _____ _____ _____ _____ enhanced the BPDU exchange and paved the way for much faster network convergence but still only allows for one root bridge per network. The bridge resources used with this protocol are higher than CST's but less that PVST+

Answer 52

IEEE 8.2/1w, Rapid Spanning-Tree Protocol (RPST)

Question 53

_____ is Cisco's version of RSTP that also uses PVST+ and provides a separate instance of 802.1w per VLAN. While it gives us really fast convergence times and optimal traffic flow, it requires the most CPU and memory of all.

Answer 53

Rapid PVST+

Question 54

What is the default convergence time for PVST+?

Answer 54

50 seconds

Question 55

As it relates to PVST+, in order to have a root bridge created per STP instance (which in the case of PVST+ is per VLAN), the BPDU is modified to include an additional field. How long is the extended system ID (VLAN ID)?

Answer 55

12 bits

Question 56

True or False: IEEE 802.1w does not offer backward compatibility.

Answer 56

False

Question 57

True or False: RPST (802.11w) requires the use of the same delay timers as CST (802.1d)

Answer 57

False

Question 58

RTSP has _____ states of transition where CST has 5.

Answer 58

3 (discarding, learning, forwarding)

Question 59

To choose the switch that will _____ on the segment, we select the switch with the lowest accumulated path cost to the root bridge.

Answer 59

forward

Question 60

When choosing which switch will forward on a segment, if there is a tie on the accumulated path cost from both switches to the root bridge, we use the _____ _____.

Answer 60

Bridge ID

Question 61

The default port priority is _____, but it can be manually changed.

Answer 61

32

Question 62

When choosing which switch will forward on a segment, if there are 2 links between switches and the bridge ID and priority are tied, the port with the _____ _____ will be chosen.

Answer 62

lowest number

Question 63

Which command is used to verify spanning-tree on a Cisco switch?

Answer 63

show spanning-tree

Question 64

What can be determined from the output of the show spanning-tree command?

Answer 64

the root bridge, priorities, and root, designated, and non-designated/blocking/discarding ports.

Question 65

To find out which is the root bridge, issue the _____ _____ _____ command, find your root port, and then use the _____ _____ _____ command.

Answer 65

show spanning tree, show cdp neighbors

Question 66

To force a bridge into the root bridge role for a particular VLAN by changing it's priority, you can issue the _____-_____ _____ _____ _____ _____ command in global configuration mode.

Answer 66

spanning-tree vlan priority

Question 67

To force a bridge into the root bridge role for a particular VLAN without having to change it's priority, you can issue the _____-_____ _____ _____ _____ _____ command in global configuration mode.

Answer 67

spanning-tree vlan root primary

Question 68

To enable RPST on a Cisco switch, you can issue the _____-_____ _____ _____-_____ command in global configuration mode.

Answer 68

spanning-tree mode rapid-pvst

Question 69

If you have a server or other devices connected into your switch that you’re totally sure won’t create a switching loop if STP is disabled, you can use a Cisco proprietary extension to the 802.1d standard called _____ on these ports.

Answer 69

PortFast

Question 70

In global configuration mode, how do you enable portfast bdpu filter?

Answer 70

S1(config)#spanning-tree portfast bpdufilter

Question 71

In global configuration mode, how do you enable portfast bpdu guard?

Answer 71

S1(config)#spanning-tree portfast bpduguard

Question 72

In global configuration mode, how do you enable portfast by default on all access ports?

Answer 72

S1(config)#spanning-tree portfast default

Question 73

From interface configuration mode, how can you enable portfast on the interface even in trunk mode?

Answer 73

S1(config-if)#spanning-tree portfast trunk

Question 74

From interface configuration mode, how can you disable portfast on the interface?

Answer 74

S1(config-if)#spanning-tree portfast disable

Question 75

If you turn on PortFast for a switch port, it’s a really good idea to turn on _____ _____ as well because if a switch port that has PortFast enabled receives a BPDU on that port, it will place the port into error disabled (shutdown) state, effectively preventing anyone from accidentally connecting another switch or hub port into a switch port configured with PortFast.

Answer 75

BPDU Guard

Question 76

you would only configure the spanning-tree bpduguard enable command on your _____ layer switches—switches where users are directly connected.

Answer 76

access

Question 77

The Cisco version of the port channel negotiation protocol is called the _____ _____ _____.

Answer 77

Port Aggregation Protocol (PAgP)

Question 78

The IEEE 802.3ad standard of the port channel negotiation protocol is called the _____ _____ _____ _____.

Answer 78

Link Aggregation Control Protocol (LACP)

Question 79

Cisco EtherChannel allows us to bundle up to _____ ports active between switches. The links must have the same speed, duplex setting, and VLAN configuration—in other words you can’t mix interface types and configurations into the same bundle.

Answer 79

8

Question 80

_____ _____ to combining two-to-eight Fast Ethernet or two-Gigabit Ethernet ports together between two switches into one aggregated logical link to achieve more bandwidth and resiliency

Answer 80

Port channeling

Question 81

_____ is Cisco’s proprietary term for port channeling.

Answer 81

EtherChannel

Question 82

_____ is a Cisco proprietary port channel negotiation protocol that aids in the automatic creation for EtherChannel links. All links in the bundle must match the same parameters (speed, duplex, VLAN info), and when _____ identifies matched links, it groups the links into an EtherChannel. This is then added to STP as a single bridge port. At this point, _____’s job is to send packets every 30 seconds to manage the link for consistency, any link additions, and failures.

Answer 82

Port Aggregation Protocol (PAgP)

Question 83

_____-_____ is a command on Ethernet interfaces used to add the specified interface to a single EtherChannel. The number following this command is the port channel ID.

Answer 83

Channel-group

Question 84

The command _____ _____-_____ creates the bundled interface. Ports can be added to this interface with the channel-group command. Keep in mind that the interface number must match the group number.

Answer 84

Interface port-channel

Question 85

You can enable your channel-group for each channel by setting the channel mode for each interface to either active or passive if using _____.

Answer 85

Link Aggregation Control Protocol (LACP)

Question 86

When a port is configured in _____ mode, it will respond to the LACP packets it receives, but it won’t initiate an LACP negotiation.

Answer 86

passive

Question 87

When a port is configured for _____ mode, the port initiates negotiations with other ports by sending LACP packets.

Answer 87

active

Question 88

You can enable your channel-group for each channel by setting the channel mode for each interface to either _____ or _____ if using LACP.

Answer 88

active, passive

Question 89

the _____ _____ _____-_____ command shows information about a specific port channel interface.

Answer 89

show etherchannel port-channel