icnd 2 trunking and vtp 2010

8/8/2019 ICND 2 Trunking and VTP 2010

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ICND2

Trunking & VTP

Rudy Drew

rudydrew@ rmit.edu.au


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Slide 2

A trunk carries traffic from multiple LANs.

Trunks connect switches to switches ORswitches to routers.


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Slide 3

1 A frame enters an access port that belongs to VLAN 200.

A port in access mode belongs to one VLAN and connects

to a PC or server. These frames are ordinary ethernetframes. The frames VLAN is known because of the VLAN

number that has been assigned to the port

(e.g. switchport access vlan 200)


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Slide 4

2 The frames on trunk links carry VLAN ID information

using dot1q encapsulation i.e. there are extra fieldsinserted into the layer 2 header.

VLAN traffic is given a VLAN ID (i.e tagged) only on

trunk links not on access port


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Slide 5

For switch ports that connect to other switches or to a

router, usually you need to set the port in in trunk mode.

VLAN traffic is tagged using dot1q or the Cisco ISL.

The standards based dot1q is used everywhere these

days.


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Slide 6

dot1q inserts a 4 byte field into the existing layer 2 header. The

VLAN ID field is 12 bits which allows for VLAN numbers up to 4094.The switch itself may only support a much smaller number of VLANse.g. 64 VLANs or 255 VLANs.

One special VLAN is called a Native VLAN. Frames belonging to thisVLAN are sent across a trunk without being tagged. The default Native

VLAN is VLAN 1 but for security this is usually changed to a different

VLAN.


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Slide 7

dot1q inserts a 4 byte field to make the frame slightly larger (a baby giant). One

of the dot1q fields (the priority field) is used forquality of service

Traffic like voice or video only works because it is given a high priority


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Slide 8

In CCNP you learn how to configure a special VLAN for

voice traffic. The tagged frames coming into the switch

belong to the voice vlan.

The untagged frames come from the PC and belong to

whatever the native VLAN is for that port.

e.g. switchport voice vlan 200

switchport access vlan 3 pmakes VLAN 3 the native

VLAN for that port.

More about this in CCNP BCMSN and ONT


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Vlan Trunking Protocol

(VTP)Create VLANs on one vtp server

switch (Sw1). Soon all of the vtp

client switches (Sw2, Sw3) in thesame VTP domain have learnt

the VLANs


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Slide 10

VLAN Trunking Protocol (VTP)

Purpose: maintain VLAN configuration

consistency across the entire domain.

Dont need to worry about typing errors when

adding vlans to other switches

e.g. -vlan)# name building_51_ITS_voice

A messaging protocol that uses Layer 2 trunk

frames to manage the addition, deletion, and

renaming of VLANs from a centralized switch that

is in the VTP server mode

Note: only VLAN information is advertised. You

still need to allocate switch ports to VLANs

manually.


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Slide 11


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Slide 13

VTP conditions:

- switch belong only to one domain.

-Cisco proprietary

-VTP frames only sent on trunk links to otherswitches in the same domain.

- 3 modes : server, client, transparent.


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Slide 14

Modes: server, client or transparent

A client switch in the same domain will change its VLAN

information to agree with the VTP advertisement sent by the VTPserver.

But a transparent mode switch willignore VTP messages butpass them to server or clients. VLANs created on transparent

switches are local only.

To turn off VTP

Sw2(config)# vtp mode transparent


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Slide 15


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Slide 17

Careful when adding a switch

The new switch should have its VLAN

information erased before being added to

the network. If not, the replacement switch

might have a revision number that makes it

seem to have newer information. Thisswitches trunking information then

replaces the existing information that is on

the switches.(The new switches existing revision

number would be what it had previously

wherever it waslocated)


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Slide 18

The newly added switch (SwitchB) has a

higher revision number. Its 7 VLANs

overwrites the existing 5 VLANs!NOTE: It doesnt matter whether the newly

introduced switch is a server or a client

icnd 2 trunking and vtp 2010

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