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CCNA > Chapter 8 - Implementing Ethernet Virtual LANs > Flashcards

Chapter 8 - Implementing Ethernet Virtual LANs Flashcards

1
Q

True or False. A switch won’t transmit frames across VLANs/Broadcast Domains.

A

True.

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2
Q

Reasons for separating devices out into VLANs.

A
  • To reduce CPU overhead on each device, improving host performance by reducing the number of devices that receive each broadcast frame.
  • To increase security by reducing the number of hosts that receive flooded frames (e.g. broadcast, multicast, and unknown unicast)
  • Security is also increased by the fact that you can implement different security policies per VLAN.
  • More flexible network designs that are also easier to manage by grouping users by commonalities (e.g. department)
  • Reduces workload for STP by reducing the amount of devices in a single broadcast domain
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3
Q

What is VLAN trunking?

A
  • Used to transmit data from multiple VLANs between switches
  • Trunking applies a VLAN tag to a frame as an extra header that includes the frame’s VLAN ID. The receiving switch will then know which VLAN each frame belongs to.
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4
Q

What are the two VLAN trunking protocols that Cisco use?

A

802.1Q and ISL (Inter-Switch Link)

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5
Q

What does 802.1Q change about frames?

A

It adds a 4-byte VLAN Tag header into frame’s header (In Ethernet this is between the Source Address and Type header). This contains a TPID (Tag Protocol Identifier), PCP (Priority Code Point), DEI (Drop Eligible Indicator), and VLAN ID (12 bits) field.

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6
Q

What is the maximum amount of VLANs you can have on a single LAN?

A

Theoretically 4096 but in practice it is 4094 as 0 and 4095 are reserved.

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7
Q

How do Cisco switches change the VLAN range?

A

They break it into two ranges; the normal range (1 to 1005) and the extended range (1006 to 4094). Only switches that support VTPv3 can use the extended range as VLANs in the extended range cannot be learnt via VTPv1 or v2.

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8
Q

What is the default native VLAN and what does it mean?

A

By default the native VLAN is VLAN 1. Traffic within the native VLAN doesn’t have a VLAN tag applied to it when sent over a trunk so the receiving switch(s) must agree on the native VLAN ID otherwise this can cause a native VLAN mistmatch.

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9
Q

True or False. Devices in different VLANs should be part of different subnets.

A

True

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10
Q

True or False. In order to communicate between VLANs a router or other layer 3 device needs to be involved.

A

True. Can’t be done at layer 2.

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11
Q

What is DTP?

A

Dynamic Trunking Protocol is a Cisco proprietary protocol that allows a port to dynamically become a trunk port or make a connected port a trunk port depending on what DTP mode is set.

-Switchport mode access - Statically sets the interface to be an access port.
Switchport mode trunk - Statically sets the interface to be a trunk port.
- Switchport mode dynamic auto - Allows the interface to passively listen for negotiate messages and be converted to a trunk port by connected interface as long as that interface is set statically to trunk or to switchport mode dynamic desirable.
- Switchport mode dynamic desirable - The interface will initiate and respond to negotiation messages, and actively attempt to convert the connected port to a trunk port as long that interface is statically set to trunk, or to switch port desirable/auto. If it is set to access it will remain this way

Setting a port statically to access will disable DTP. Setting a port statically to trunk will leave DTP enabled.

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12
Q

What is VTP?

A

VLAN Trunking Protocol is a Cisco proprietary protocol that advertises VLAN information on one switch to all other switches on the same VTP domain. VTP settings (Domain, Password, Version) must match for it to function.
- Server mode - The default VTP mode. All changes made on a switch in this mode will be advertised to client switches.
- Client mode - In this mode switches will receive updates from VTP servers and also forward updates to other switches.
- Transparent - A transparent switch will not advertise VLAN configuration or synchronize its own to that of its server(s) but will forward updates to other switches.

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13
Q

What is the DTP Administrative Mode and Operational Mode?

A
  • Administrative mode is what is configured on the switch port.
  • Operational mode is the actual status of the port. (e.g. If administrative mode is set to dynamic auto, the operational mode would be trunk if the opposite switchport is set to trunk or dynamic desirable).
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14
Q

What is the command used to specifically define a voice VLAN?

A

switchport voice vlan <vlan-id></vlan-id>

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15
Q

True or False. Switches will not forward VLAN traffic for VLANs that are not defined in said switch or has not been learned via VTP.

A

True. They will also not forward VLAN traffic for VLANs that have been shutdown.

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16
Q

What does VLAN status ‘act/lshut’ mean?

A

This VLAN is currently shutdown.

17
Q

What issues can occur from having mismatched trunking Operational states between switches?

A

Examples:
-If both switches are set to Operational mode Dynamic Auto they will both passively wait for the other device to negotiate which will never occur.

-If one switch is set as trunking and the other is set as access then the access switch will discard any frames with an 802.1Q header not part of the same VLAN as the access port. All frames will have an 802.1Q header since the trunk tags them. If they are part of the native VLAN however, they will pass as normal as they don’t have an 802.1Q header and the access port will assume the traffic is part of its VLAN even if it isn’t.

18
Q

True or False. By default all VLANs defined on a device will be forwarded by a trunk port.

A

True. In order to negate this you would need to configure the ‘switchport trunk allowed vlan <vlan-id>' command.</vlan-id>

19
Q

Define the headings displayed by the ‘show interfaces trunk’ command.

A
  • VLANs allowed on trunk - Shows all VLANs defined on the switch that are allowed to be forwarded by a trunk port. Use the ‘switchport trunk allowed vlan’ command.
  • VLANs allowed and active in management (VTP) domain - VLANs in the first header that haven’t been shutdown and are active on this switch.
  • VLANs in spanning tree forwarding state and not pruned - The same as the second list minus VLANs in an STP blocking state for the specified interface and VLANs that have been pruned from this trunk via VTP
20
Q

What is a native VLAN mismatch?

A

When two connected switches have a different native VLAN on their trunk ports.

(For example SW1 has its native VLAN as 10 and SW2 has its native VLAN as 20. A device on SW1 (VLAN 10) pings a device on SW2 that is connected to an access port for VLAN 10. When the ping leaves SW1 it will not be tagged as this is the native VLAN, however when it reaches SW2 without a tag, SW2 will consider it to be part of its own native VLAN (VLAN 20) and therefore won’t forward the ping to VLAN 10.)

21
Q

True or False. Traffic traversing the trunk link in the trunks native VLAN will be tagged with the trunk’s native VLAN.

A

False. Traffic from the native VLAN will traverse the link untagged so once it reaches the other end this will be considered to be part of the other switches native VLAN also. If the native VLAN matches on both ends this won’t cause an issue

22
Q

What is a Management VLAN?

A

A VLAN that only network devices will be able to access and receive an IP address from. This is used to login directly to the device. Switches do not build ARP tables aside from for management addresses (e.g. the IP of a router that is also part of this VLAN).

23
Q

What are the different fields of a 802.1Q header?

A
  • TPID (Tag Protocol Identifier) (16 bits) - Always has a value of 0x8100. This indicates the frame is 802.1Q tagged.
  • TCI PCP (Priority Code Point) (3 bits) - Used for CoS (Class of Service) which prioritizes important traffic in congested networks.
  • TCI DEI (Drop Eligible Indicator) (1 bit) - Indicates frames that can be dropped if the network is congested.
  • TCI VID (VLAN ID) (12 bits) - Identifies the VLAN tag.
24
Q

What is the default 802.1Q trunking setting for Cisco switches?

A

dynamic auto

25
Q

True or False. VTP updates can only be sent over a trunk.

A

True. VTP domains cannot cross routers for this reason.

26
Q

What is a Voice VLAN?

A
  • A VLAN dedicated to IP voice traffic
  • If an interface has a voice VLAN set, this traffic will be received as tagged by the interface but the port can still be access. If there is also a data VLAN on this interface traffic will be received in that as untagged.
  • A switch can use CDP to tell a VOIP phone that any traffic sent in the voice VLAN must be tagged.
27
Q

What VTP mode do switches operate in by default?

A

Server

28
Q

What do VTP servers do?

A
  • Add, modify, and delete VLANs on VTP domains
  • Store VLAN database in NVRAM
  • Increase their revision number everytime a VLAN is added, modified, or deleted
  • Advetise the latest version of their VLAN database on trunk interfaces so clients can sync to it
  • VTP servers will also function as clients and will sync to other servers with a higher revision number
29
Q

What do VTP clients do?

A
  • Cannot add, modify, and delete VLANs on VTP domains
  • Do not store their VLAN database in NVRAM (unless using v3)
  • Will sync their VLAN database to the server in their domain with the highest revision number
  • Will advertise their VLAN database and forward VTP updates to other clients over trunk ports
30
Q

What will happen if a switch with no VTP domain name (NULL) receives a VTP advertisement with a VTP domain name?

A

It will automatically join that VTP domain

31
Q

What does a VTP switch in transparent mode do?

A
  • Does not participate in any VTP domain and sync its VLAN database
  • Maintains its own VLAN database in NVRAM. Any VLANs added, created, or deleted will not be advertised
  • Will forward VTP advertisements for servers in the same domain
32
Q

True or False. Changing the VTP domain name will set the revision number to 0.

A

True. This will also happen if the switch is set to Transparent.

CCNA (50 decks)

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