1 - Implementing Ethernet VLANs Flashcards

Ch 1

1
Q

6 Reasons for using VLANs

A
  • Reduce CPU and broadcasts
  • Reduce Security Risks
  • Improve Security of sensitive data
  • Flexible design by grouping users by department
  • Troubleshoot quicker by reducing failure domain
  • Reduce STP workload by keeping one VLAN per switch.
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2
Q

What VLANs are in the normal range?

A

1 - 1005

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3
Q

What VLANs are in the extended range?

A

1006 - 4094

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4
Q

How does 802.1q tag a frame?

A

Adds a 4-byte header into the Ethernet header between the Source and Type fields.

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5
Q

Is the native VLAN tagged?

A

No

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6
Q

When configuring ROAS what are the two ways to define the native VLAN?

A
  • Use the physical interface with no ENCAP command
  • Use a subinterface with ‘encap dot1q 10 native’
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7
Q

For ROAS, how do you configure the physical interface to use the native VLAN

A

Add IP address for native VLAN, NO ENCAP and NO VLAN parameter.

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8
Q

For ROAS, what are the commands used to configure a subinterface to use the native VLAN?

A
  • int fa0/0.1
    • encap dot1q 10 native
    • ip address 172.21.10.1 255.255.255.0
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9
Q

What VLANs cannot be deleted?

A

1, and 1002 - 1005

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10
Q

What commands can be used to disable VTP?

A
  • vtp mode transparent
  • vtp mode off
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11
Q

If connecting two switches with a trunk and both switches support ISL and 802.1q, which protocol will they choose?

A

ISL

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12
Q

Which protocol do switches use to negotiate trunking?

A

Dynamic Trunking Protocol (DTP)

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13
Q

What 2 configuration options are negotiated by DTP?

A
  • administrative mode (always trunk, never trunk, or negotiate)
  • Type of Trunking: ISL or dot1q,
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14
Q

What are possible administrative modes of a switchport?

A
  • access
  • trunk
  • dynamic desireable
  • dynamic auto
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15
Q

What is the default administrative mode of a switchport?

A

dynamic auto

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16
Q

What is the switchport command to disable DTP

A

switchport nonegotiate

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17
Q

Will the ‘show interfaces trunk’ command show IP phone trunks?

A

No.

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18
Q

What show command will show IP phone trunks?

A

show interfaces f0/4 trunk

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19
Q

If VTP is disabled and a new VLAN is configured on a new switch, where will the VLAN configuration be seen?

A

show running-config’

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20
Q

What range of VLANs do older low end switches support?

A

Normal-range 1 - 1005

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21
Q

What range of VLANs do new switches and high-end switches support?

A
  • Normal-range: 1 - 1005
  • Extended-range: 1006 - 4094
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22
Q

Assuming a default trunking configuration, what is the term that is used to reference the VLAN that will be used to transport the traffic between the hosts in the default VLAN?

A

Native

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23
Q

In ‘show interfaces gig0/1 switchport’ cmd what does ‘Administrative Trunking Encapsulation: negotiate’ mean?

A

It means the switch supports both dot1q and ISL.

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24
Q

How can you tell what trunking encapsulation is supported by a switch?

A

Run the cmd ‘show interfaces gig0/1 switchport’. Check the Administrative Trunking Encapsulation field.

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25
Q

What is the command to configure a voice VLAN on a switchport?

A

switchport voice vlan 12

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26
Q

What management protocol must be running on a switchport to enable it to be used by a Cisco phone?

A

CDP, which is enabled by default.

27
Q

In the dot1q header why does the 12-bit VLAN_ID field only support 4094 VLANs?

A

There are two reserved values: 0 and 4095.

28
Q

What are the fields in an 802.1q tag?

A
  • TPI (Tag Protocol Identifier) always 0x8100 2 bytes
  • TCI (Tag Control Information) made up of: PCP (Priority Code Point) 3 bits
  • DEI (Drop Eligibility Indicator) 1 bit
  • VID (VLAN Identifier) 12-bits
29
Q

What are the 5 different states a port transitions through?

A
  1. Disabled
  2. Blocking
  3. Listening
  4. Learning
  5. Forwarding
30
Q

What is the Forward Delay?

A

The time it takes for a port to transition from Listening to Learning and from Learning to Forwarding. The default for Forward Delay is 15 seconds.

31
Q

In what states do port populate the MAC address table?

A

Learning and Forwarding only

32
Q

What causes STP convergence?

A

Topology Changes. Adding a switch or a link goes down.

33
Q

What happens during Convergence?

A
  • All data stops until convergence is complete.
  • Ports transition to forwarding or blocking state.
  • With 802.1d STP this process takes 50 seconds.
34
Q

What is the difference between Port Cost and Path Cost?

A
  • Port Cost is based on the speed of the link.
  • Path cost is the sum of all the Port Costs all the way to the root.
35
Q

What are all ports called on the Root Bridge?

A

Designated Ports (DP)

36
Q

On a segment that doesn’t connect to the Root Bridge how is the Designated Port chosen?

A

The switch with the lowest (best) Bridge ID will be chosen to have the Designated Port for that segment. By default, the other port is placed in Blocking state.

37
Q

What is the advantage of PVST over Common STP?

A

Per VLAN Spanning Tree allows for multiple root bridges. (different root for each VLAN is possible).

38
Q

What are the 5 types of Spanning Tree Protocols?

A
  1. Common Spanning Tree 802.1d (single root bridge)
  2. PVST+ Cisco’s Default version
  3. 802.1w IEEE version of Rapid Spanning Tree (single root bridge)
  4. 802.1s MSTP (basically instances of STP running on top of one STP
  5. Rapid PVST+
39
Q

In Rapid PVST+ how is the DP chosen?

A
  1. Lowest accumulated Path Cost to the Root
  2. If Path Cost is a tie then use Bridge ID
  3. If a tie after Path Cost, Bridge ID, then interface with Lowest Number (Fa0/1 wins over FA0/2)
40
Q

In PVST+ what impact does the VLAN number have on the Bridge Priority?

A

Add VLAN # to Priority. 32,768 on VLAN 10 would be 32,778

41
Q

What is the command to enable Rapid PVST+?

A

spanning-tree mode rapid-pvst

42
Q

What are the two port-channel negotiating protocols?

A

PAgP and LACP

43
Q

What are the two possible Interface Modes for LACP?

A

Active or Passive

44
Q

What are the two Interface Modes for PAgP?

A

Auto or Desirable

45
Q

What is the difference between PAgP and LACP?

A

PAgP is Cisco Proprietary, LACP is IEEE Non-proprietary

46
Q

In a Port-channel does the Port-channel inherit its configuration from the Interfaces or do the Interfaces inherit their configurations from the Port-channel?

A

The Interfaces inherit their configurations from the port-channel

47
Q

What command will show you the STP root bridge for a VLAN?

A

show spanning-tree summary

48
Q

What command will you use to see information about a specific port channel interface?

A

show etherchannel port-channel

49
Q

What command would you use on a switch to make it the root bridge for VLAN 3?

A

spanning-tree vlan 3 root primary

50
Q

You need to find the VLANs for which your switch is the root bridge. What two commands can you use?

A
  • ‘show spanning-tree summary’
  • ‘show spanning-tree’ and then follow the root ports using CDP
51
Q

You want to create a port-channel. What command do you use? Assume PAgP.

A
  • interface port-channel 1
  • exit
  • interface range gig0/12-13
  • channel-group 1 mode desirable
    *
52
Q

You want to create a port-channel. What commands do you use to create the port-channel? Assume LACP.

A
  • interface port-channel 1
  • exit
  • interface range gig0/12-13
  • channel-group 1 mode active
53
Q

What are the commands to create a L3 port-channel on a switch using PAgP?

A
  • interface port-channel 1
    • no switchport
    • ip address 172.21.7.42 255.255.255.0
    • exit
  • interface range gig0/12-13
    • no switchport
    • channel-group 1 mode desirable
54
Q

When the command ‘spanning-tree vlan 3 root primary’ is issued what priority does it give that switch?

A

If current root base priority is higher than 24,576 it will set the base priority to 24,576 + VLAN. If the current root bridge is less than 24,576 it will set the new priority to the highest multiple of 4096 that still results in that switch becoming the new root.

55
Q

When the command ‘spanning-tree vlan 3 root secondary’ is issued what priority does it give that switch?

A

28,672 + 3

56
Q

How many bits is the sys-id-ext field in a BPDU?

A

12

57
Q

In RSTP what is an Alternate Port?

A

A port waiting to become a Root Port

58
Q

In RSTP what is a Backup Port?

A

A port waiting to become a Designated Port

59
Q

Which VLANs cannot be used?

A

1002 - 1005

60
Q

What command configures an switchport to use 802.1q encapsulation for trunking?

A

switchport trunk encapsulation dot1q

61
Q

What command configures a switchport to use ISL trunking?

A

switchport trunk encapsulation isl

62
Q

What command is used to tell a switchport to negotiate the type of trunking?

A

switchport trunk encapsulation negotiate

63
Q

What command tells an interface to begin trying to negotiate trunking?

A

switchport mode dynamic desirable