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What is VTP?

VTP allows a network manager to configure a switch so that it will propagate VLAN

configurations to other switches in the network. The switch can be configured in the role of a

VTP server or a VTP client. VTP only learns about normal-range VLANs (VLAN IDs 1 to 1005).

Extended-range VLANs (IDs greater than 1005) are not supported by VTP.

VTP stores VLAN configurations in the VLAN database called vlan.dat.

VTP advertisements will not be exchanged if the trunk between the switches is inactive.

VTP Domain-Consists of one or more interconnected switches. All switches in a domain share

VLAN configuration details using VTP advertisements. VTP Advertisements-VTP uses a

hierarchy of advertisements to distribute and synchronize VLAN configurations across the

network. VTP Modes- A switch can be configured in one of three modes: server, client, or

transparent.

VTP Modes- A switch can be configured in one of three modes: server, client, or transparent.

VTP Client-VTP clients function the same way as VTP servers, but you cannot create, change, or

delete VLANs on a VTP client. A VTP client only stores the VLAN information for the entire

domain while the switch is on. A switch reset deletes the VLAN information. You must

configure VTP client mode on a switch.

VTP Transparent-Transparent switches forward VTP advertisements to VTP clients and VTP

servers. Transparent switches do not participate in VTP. VLANs that are created, renamed, or

deleted on transparent switches are local to that switch only.

Corte de VTP - O corte de VTP aumenta a largura de banda disponvel na rede restringindo o

trfego inundado aos links tronco que o trfego deve utilizar para alcanar os dispositivos de

destino. Sem o corte de VTP, um switch inunda o trfego de broadcast, multicast e unicast

desconhecido para todos os links tronco dentro de um domnio VTP mesmo que os switches de

recebimento o descartem.

VTP Versions

VTP has three versions, 1, 2, and 3. Only one VTP version is allowed in a VTP domain. The

default is VTP version 1. A Cisco 2960 switch supports VTP version 2, but it is disabled.

A VTP domain consists of one switch or several interconnected switches sharing the same VTP

domain name. Until the VTP domain name is specified you cannot create or modify VLANs on a

VTP server, and VLAN information is not propagated over the network. When switches are in

different VTP domains, they do not exchange VTP messages. A VTP server propagates the VTP

domain name to all switches for you. Domain name propagation uses three VTP components:

servers, clients, and advertisements.

VTP Frame Encapsulation

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A VTP frame consists of a header field and a message field. The VTP information is inserted

into the data field of an Ethernet frame. The Ethernet frame is then encapsulated as a 802.1Q

trunk frame (or ISL frame). Each switch in the domain sends periodic advertisements out each

trunk port to a reserved multicast address. These advertisements are received by neighboring

switches, which update their VTP and VLAN configurations as necessary.

VTP frames contain the following fixed-length global domain information:

VTP domain name

Identity of the switch sending the message, and the time it was sent

MD5 digest VLAN configuration, including maximum transmission unit (MTU) size for each

VLAN

Frame format: ISL or 802.1Q

VTP frames contain the following information for each configured VLAN:

VLAN IDs (IEEE 802.1Q)

VLAN name

VLAN type

VLAN state

Additional VLAN configuration information specific to the VLAN type

Note: A VTP frame is encapsulated in an 802.1Q Ethernet frame. The entire 802.1Q Ethernet

frame is the VTP advertisement often called a VTP message. Often the terms frame,

advertisement, and message are used interchangeably.

Each time a VLAN is added or removed, the configuration revision number is incremented.

Each VTP device tracks the VTP configuration revision number that is assigned to it.

Note: A VTP domain name change does not increment the revision number. Instead, it resets

the revision number to zero.

The configuration revision number determines whether the configuration information received

from another VTP-enabled switch is more recent than the version stored on the switch.

Summary Advertisements

The summary advertisement contains the VTP domain name, the current revision number, and

other VTP configuration details.

Summary advertisements are sent(exchange to each other)

Every 5 minutes by a VTP server or client to inform neighboring VTP-enabled switches of the

current VTP configuration revision number for its VTP domain

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Immediately after a configuration has been made

Subset Advertisements

A subset advertisement contains VLAN information. Changes that trigger the subset

advertisement include:

Creating or deleting a VLAN

Suspending or activating a VLAN

Changing the name of a VLAN

Changing the MTU of a VLAN

Request Advertisements

When a request advertisement is sent to a VTP server in the same VTP domain, the VTP serverresponds by sending a summary advertisement and then a subset advertisement.(Ver o video

do slide 4.2.3.4)

Request advertisements are sent if:

The VTP domain name has been changed

The switch receives a summary advertisement with a higher configuration revision number

than its own(after the switch know that there are a change on revision then they request

advertisement)

A subset advertisement message is missed for some reason

The switch has been reset

Request Advertisements

When a request advertisement is sent to a VTP server in the same VTP domain, the VTP server

responds by sending a summary advertisement and then a subset advertisement.

Request advertisements are sent if:

The VTP domain name has been changed

The switch receives a summary advertisement with a higher configuration revision number

than its own

A subset advertisement message is missed for some reason

The switch has been reset

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VTP pruning prevents unnecessary flooding of broadcast information from one VLAN across all

trunks in a VTP domain.

S4, which has been previously configured as a VTP client, is added to the network. The revision

number of the switch S4 is 35, which is higher than the revision number of 17 in the existing

network. S4 comes preconfigured with two VLANs, 30 and 40, that are not configured in theexisting network. The existing network has VLANs 10 and 20.

When switch S4 is connected to switch S3, VTP summary advertisements announce the arrival

of a VTP-enabled switch with the highest revision number in the network. The animation

shows how switch S3, switch S1, and finally switch S2 all reconfigure themselves to the

configuration found in switch S4.

When a new VLAN, for example, VLAN 10, is added to the network, the network manager adds

the VLAN to the VTP server, switch S1 in the figure. As you know, VTP takes care of

propagating the VLAN configuration details to the rest of the network. It does not have any

effect on which ports are configured in VLAN 10 on switches S1, S2, and S3.

VTP pruning is disabled by default in Cisco switches. VTP pruning helps to send broadcastsonly to those trunk links that actually needs the information. For example, if switch A does nothave a port configured for VLAN 7, and broadcast is sent throughout VLAN 7, that broadcast ortraffic will not pass through the trunk link to switch A.