Ethernet, VLANs, and Spanning Tree Protocol

Question 0

Which switch port setting will be automatically detected even if auto-negotiation is disabled? What does it use to do this?

Answer 0

Speed. The switch uses the incoming electrical signal.

Question 1

What Cisco switch feature automatically detects crossover and straight-through cables and swaps the pairs its ports use so copper Ethernet works properly?

Answer 1

Auto-MDIX

Officially, automatic medium-dependent interface crossover

Question 2

What function in auto-negotiation does a switch use to determine port speed?

Answer 2

Fast Link Pulses

Question 3

How does a switch choose a duplex setting if auto-negotiation is disabled?

Answer 3

It uses the default setting for the port speed.

Question 4

What is the default duplex setting for:
A) 10BaseT
B) 100BaseT
C) 1000BaseT

Answer 4

A) half
B) half
C) full

Question 5

How can you disable switch port auto-negotiation?

Answer 5

Statically configure the port speed and duplex.

Question 6

What Ethernet port setting uses loopback circuitry?

Answer 6

Half duplex

Question 7

When configuring speed and duplex manually, which must be set first?

Answer 7

Speed

Question 8

Name the two most common forms of Ethernet framing.

Answer 8

Ethernet V2 and 802.3.

Question 9

How can an Ethernet V2 frame indicate the protocol contained within it?

Answer 9

Via its Type field.

Question 10

What are the two ways an 802.3 Ethernet frame can signal what type of traffic is contained within it?

Answer 10

An 802.2 (or LLC) field or a SNAP header with a Type field.

Question 11

What does 802.2 use to announce the traffic type contained within the Ethernet frame?

Answer 11

An SSAP and a DSAP.

Question 12

What makes the bits in an Ethernet address byte different from the rest of the Ethernet frame? Name two terms for this bit setup.

Answer 12

The bits move right-to-left in order of significance. This is called canonical or little-endian.

Question 13

What is the 8th bit in the first byte of an Ethernet address used for? What’s the term for it?

Answer 13

It’s used to identify the address as unicast (0) or multicast (1). It’s called the I/G bit.

Question 14

What’s the 7th bit in the first byte of an Ethernet address used for? What’s the term for it?

Answer 14

It identifies whether the address is assigned by the hardware vendor (0) or whether it’s been set by an administrator (1). The term is U/L, for Universal/Local.

Question 15

What’s the OUI for an Ethernet multicast address?

Answer 15

0x01005E

Question 16

Give the length of a SNAP header and the 802.2 DSAP that signifies it’s there.

Answer 16

2 bytes; 0xAA

Question 17

What’s the IEEE designation for Fast Ethernet?

Answer 17

802.3u

Question 18

What’s the IEEE designation for GigE over fiber?

Answer 18

802.3z

Question 19

What’s the IEEE designation for GigE over copper?

Answer 19

802.3ab

Question 20

What command displays the Ethernet addresses known to a switch?

Answer 20

Switch> show mac address-table

Question 21

Give the maximum distance for 1000BaseLX in each of MM and SM.

Answer 21

MM 3 km, SM 10 km

Question 22

Give the maximum distance for 1000BaseSX in each of 62.5-micron and 50-micron fiber.

Answer 22

62.5-micron 220 m, 50-micron 550m

Question 23

Give the maximum length of 1000BaseZX.

Answer 23

100 km

Question 24

What's the best practice with respect to VLANs and IP addressing?

Answer 24

Maintain a one-to-one relationship between VLANs and IP subnets.

Question 25

What are the three tasks one can perform in VLAN configuration mode?

Answer 25

1. Create VLANs 2. Set basic administration parameters 3. Verify VTP configuration

Question 26

What VLANs can be configured in VLAN configuration mode?

Answer 26

Normal-range VLANs (1-1005)

Question 27

Where is the VLAN database stored? What's the filename?

Answer 27

Flash; vlan.dat

Question 28

Give the VLAN configuration mode commands that: 1. Display the VLANs that are actively configured on the switch. 2. Display the VLANs that will be in place after configuration changes are finalized.

Answer 28

1. show current | 2. show proposed

Question 29

Give the VLAN configuration mode commands that: 1. Implement the proposed configuration without leaving VLAN configuration mode. 2. Cancel changes and leave VLAN configuration mode. 3. Cancel the changes and stay in VLAN configuration mode.

Answer 29

1. apply 2. abort 3. reset

Question 30

Give the VLAN configuration database command that creates VLAN #15 and titles it cisco.

Answer 30

vlan 15 name cisco

Question 31

Give the command that can be used in interface configuration mode to create VLAN 15 and assign it to the interface.

Answer 31

(config-if)# switchport access vlan 15

Question 32

What distinguishes a primary VLAN from a secondary VLAN in a private VLAN?

Answer 32

The primary VLAN is promiscuous; its members can talk to any other member of the private VLAN. Members of a secondary VLAN can talk to each other and to members of the primary VLAN.

Question 33

Name and briefly describe the two types of secondary VLANs.

Answer 33

Community VLANs have multiple members that talk to each other. Isolated VLANs have a single member that can only communicate with members of the primary VLAN.

Question 34

Name the three items that VTP advertises about a VLAN.

Answer 34

1. VLAN ID 2. VLAN name 3. VLAN type (Ethernet, Token Ring, etc.)

Question 35

What VTP mode(s) issue(s) advertisements?

Answer 35

Server and client

Question 36

What VTP mode(s) forward(s) received VTP advertisements?

Answer 36

Server, client, and transparent

Question 37

What VTP mode(s) allow(s) you to create or modify VLANs using configuration commands?

Answer 37

Server and transparent

Question 38

How does a VTP domain track changes to try to ensure that the most current configuration is on each switch?

Answer 38

It uses VTP revision numbers.

Question 39

What is the default VTP mode on a switch?

Answer 39

Server

Question 40

What causes a switch to start sending VTP updates?

Answer 40

When the VTP domain name is set.

Question 41

How could a switch configured as a VTP client inadvertently get the wrong VTP information?

Answer 41

It could receive a VTP announcement from the wrong domain first. VTP clients adopt the first VTP domain name they see.

Question 42

A VTP domain should have at least how many VTP servers?

Answer 42

2

Question 43

Where do VTP servers store their vlan.dat files? How about VTP clients?

Answer 43

Both store the files in flash. (Depending on the model, some can store vlan.dat in NVRAM, too)

Question 44

How can you prevent DoS attacks via VTP?

Answer 44

Set a VTP password.

Question 45

What encryption do VTP passwords use?

Answer 45

MD5

Question 46

Give the command that sets a switch's VTP mode to transparent.

Answer 46

(config)# vtp mode transparent

Question 47

Give the commands that define a switch's VTP domain as CCIE-domain and the password as CCIE.

Answer 47

(config) # vtp domain CCIE-domain | (config) # vtp password CCIE

Question 48

True or False: VTP domain names are case-sensitive.

Answer 48

True

Question 49

What is the range of normal VLAN numbers?

Answer 49

1-1001

Question 50

What is the extended range of VLAN numbers?

Answer 50

1006-4094

Question 51

What VLAN number is reserved and cannot be used?

Answer 51

0

Question 52

What VLAN number range(s) can be pruned by VTP?

Answer 52

2-1001 | these are also the VLANs that can be advertised

Question 53

Which VLAN mode(s) can use extended VLANs?

Answer 53

VTP transparent mode

Question 55

Where does a switch in VTP transparent mode store extended-range VLAN configuration commands?

Answer 55

Running configuration only

Question 56

Which VLAN identification method(s) support(s) extended-range VLANs?

Answer 56

Both ISL and 802.1Q

Question 57

Which VLAN identification method(s) support(s) the concept of a native VLAN?

Answer 57

802.1Q only

Question 58

What concept does ISL use to support trunking?

Answer 58

Encapsulation--it puts a new header around data.

Question 59

By how much does ISL increase the size of an Ethernet frame?

Answer 59

26 bytes (the size of the header)

Question 60

Looking at a frame on an ISL-trunked link, how could you determine that the frame is using ISL?

Answer 60

The frame has a source MAC of the device performing the trunking and a destination MAC of 0100.0C00.0000 or 0300.0C00.0000.

Question 61

Where does a switch in VTP transparent mode store normal-range VLAN information?

Answer 61

In both vlan.dat (Flash) and running configuration.

Question 62

How many bytes does 802.1Q add to an Ethernet frame?

Answer 62

4

Question 63

How does 802.1Q signal to devices that a tag exists?

Answer 63

The first two bytes of the tag are an EtherType of 0x8100.

Question 64

How does the native VLAN option in 802.1Q add resiliency to an Ethernet network?

Answer 64

It allows the switch to attempt to continue sending data on the native VLAN even if trunking fails.

Question 65

What is the default DTP mode?

Answer 65

Desirable

Question 66

Give the commands that display: 1. A summary of trunk-related information 2. Trunking details for interface g0/0 3. Nontrunking details for interface g0/0

Answer 66

1. show interface trunk 2. show interface g0/0 trunk 3. show interface g0/0 switchport

Question 67

What command allows you to administratively forbid VLANs from existing over a trunk?

Answer 67

switchport trunk allowed

Question 68

What two conditions must be present for a VLAN to be active on a trunk?

Answer 68

It must be allowed on the trunk and configured on the switch.

Question 69

Give the interface configuration commands that tell the switch to do the following: 1. Always trunk on this end; send DTP to inform the other side. 2. Don't send DTP messages. 3. Initiate DTP conversations and trunk if negotiation succeeds. 4. Listen for DTP and trunk if negotiation succeeds.

Answer 69

1. switchport mode trunk 2. switchport nonegotiate 3. switchport mode dynamic desirable 4. switchport mode dynamic auto

Question 70

How can routers learn about trunking interfaces?

Answer 70

Via manual configuration--there's no DTP support.

Question 71

Give the command that you'd put on a router sub-interface to indicate that VLAN 201, the VLAN for this sub-interface, is the 802.1Q native VLAN.

Answer 71

(config-subif)# encapsulation dot1q 201 native

Question 72

True or False: VTP can pass over a Q-in-Q service, but CDP cannot.

Answer 72

False--both can pass over Q-in-Q.

Question 73

Give the three parts of the STP bridge ID in later STP implementations like PVST+ and MST. Give the length of each.

Answer 73

Priority: 4 bits System ID Extension (VLAN ID): 12 bits System ID (MAC Address): 48 bits

Question 74

What four fields does a switch update in a Hello BPDU from the root bridge before forwarding it out to neighbors?

Answer 74

Cost Bridge ID (puts its own ID in the BPDU) Port priority Port number

Question 75

True or False: Bridges forward Hello BPDUs out ports they are blocking so other bridges know they are a potential future path to the root.

Answer 75

False

Question 76

List the four items a switch uses to choose its root port by order of relevance.

Answer 76

1. Cost 2. Lowest forwarding bridge ID 3. Lowest port priority from the forwarding bridge 4. Lowest port number from the forwarding bridge

Question 77

What's the default port priority? How about the range?

Answer 77

128. Range is 0-240 by 16s.

Question 78

How is the designated port for a segment determined?

Answer 78

Cost, bridge ID, port priority, port number (same as root port)

Question 79

What are the default STP Hello and Maxage timers?

Answer 79

2 seconds and 20 seconds (Maxage is 10x Hello)

Question 80

Under what circumstance does a switch not have to wait for the Maxage timer to expire to declare a link down?

Answer 80

When the link is a failed port channel.

Question 81

Give the revised IEEE and 802.1t STP costs, respectively, for the following Ethernet speeds: 1. 10 Mbps 2. 100 Mbps 3. 1 Gbps 4. 10 Gbps

Answer 81

1. 100; 2,000,000 2. 19; 200,000 3. 4; 20,000 4. 2; 2,000

Question 82

What will a switch that experiences a topology change do? What will other switches do to help out?

Answer 82

The switch will send a Topology Change Notification BPDU out its root port. Switches upstream forward the TCN toward the root and send back Hellos with the TCA bit marked.

Question 83

How does a root bridge respond to an advertised change in topology?

Answer 83

It sends Hellos marked with TCAs out all ports, ensuring that all switches in the network learn that there has been a topology change.

Question 84

How will a switch that receives a Hello BPDU marked with the TCA bit change its behavior?

Answer 84

It will use the Forward Delay timer to age out CAM entries.

Question 85

What is the default for the STP Forward Delay timer?

Answer 85

15 seconds

Question 86

What are the transitory STP states?

Answer 86

Listening and Learning

Question 88

How does PVST+ differ from traditional STP?

Answer 88

It allows for a different root bridge and blocking interfaces per VLAN.

Question 89

How does PVST+ treat non-Cisco switches in an 802.1Q environment? What happens in the non-Cisco switches?

Answer 89

It views them as a single link over to Cisco switches on the other side. The non-Cisco switches have a Common Spanning Tree for all VLANs.

Question 90

How do Cisco switches communicate PVST+ information across a non-Cisco switching domain?

Answer 90

They set their BPDUs with the multicast destination of 0100.0CCC.CCCD, which the non-Cisco switches see as standard multicast and forward to the other side.

Question 91

Give the switch command that tells you details about the root bridge. What information in the output of this command would tell you that you're looking at the root bridge?

Answer 91

show spanning-tree root You're looking at the root bridge if the cost listed is 0.

Question 92

What's the difference between the STP Listening and Learning states?

Answer 92

During the Learning state, the switch learns MAC addresses from received frames.