CCNA 3 Week 9 VLAN Trunking. Copyright © 2005 University of Bolton Origins Dates back to radio and...

CCNA 3 Week 9

VLAN Trunking

Copyright © 2005 University of BoltonCopyright © 2005 University of Bolton

Origins

Dates back to radio and telephone

Trunk carries multiple channels over a single link

Single link between switches carrying multiple VLANS


Lan Trunking

Trunking saves ports and reduces wiring between switches

Removes complexity from physical hardware


Trunking Operation

Need a method to identify which frames are destined for each subnet/VLAN

– Filtering– Tagging


IEEE 802.1Q

Switches need to be able to determine which VLAN frames from a trunk should be passed to

Cisco offers Propriatary ISL or 802.1Q

802.1Q protocol includes VLAN tagging as part of layer 2 frames

Standard protocol used by many manufacturers


Frame Tagging

Frames have a VLAN id inserted into Frame header

Understood and read by switches

VLAN identifier removed before traffic leaves trunked/backbone links


Setup Trunking

Commands to enable trunkingSw1(config)# interface fastethernet0/1Sw1(config-if)# switchport mode trunkSw1(config-if)# switchport trunk encapsulation dot1qSw1(config-if)# end

Naturally need to enable trunking at each end of a trunked link

VLAN Trunking Protocol


History of VTP

Protocol created by Cisco

Need consistency in VLAN numbering to allow trunking across large network

Either have to manage each switch individually

Manage centrally to ensure consistency

Otherwise risk cross-connection or failure to pass on frames


VTP Concepts

VTP uses layer 2 trunk frames to Add, Delete and Rename VLANs

VTP messages encapsulated in ISL or 802.1q


VTP Messages

Contain the following– VTP protocol version - Either version 1 or 2 – VTP message type - Indicates one of four types of

messages – Management domain name length - Indicates the size

of the name that follows – Management domain name - Name configured for the

management domain


VTP Modes

VLAN Server– Can create/modify/delete vlans for entire domain– Save VLAN config in NVRAM– Send VTP messages to all trunk ports

VLAN Client– Cannot make changes– Record information and forward VTP messages

Transparent Mode– Forward Messages but ignore content– Can create local VLANs


VTP Implementation

Each switch advertises multicasts via trunk ports– its management domain– configuration revision number– the VLANs that it knows about

Clients request info at bootup, servers respond


Summary Advertisements

Sent every five minutes with current VTP revision number

If greater that the receiver's revision number, an advertisement request is sent


Subset Advertisements

Subset advertisements contain detailed information about VLANs

– VTP version type– Domain name – Configuration revision number.

Certain actions can trigger subset advertisements:– VLAN creation or deletion – VLAN suspension or activation – VLAN name change – VLAN maximum transmission unit (MTU) change


Advertisement Contents

Management domain name - Advertisements with different names are ignored.

Configuration revision number - The higher number indicates a more recent configuration.

Message Digest 5 (MD5) - MD5 is the key that is sent with the VTP when a password has been assigned. If the key does not match, the update is ignored.

Updater identity - The updater identity is the identity of the switch that sends the VTP summary advertisement.


VTP Configuration

Determine the version number of VTP that will be utilized.

Is a new management domain needed

To join an existing domain, name and password are needed

Choose a VTP mode for the switch– V1 and V2 not interoperable


VTP Commands

Switch#vlan database

Switch(vlan)#vtp v2-mode

Switch(vlan)#vtp domain cisco

Switch(vlan)#vtp {client | server | transparent}

Routers and VLANs


Need for routers

To pass traffic between subnets(VLANs) a router is required

Segment broadcast domains

Trunks may connect to router


Routers Trunked Links

Not cost effective to have dedicated ethernet port per vlan

Can split physical interface into logical sub-interfaces

A logical interface for each subnet


Sub-interfaces

A logical interface within a physical interface

Each sub-interface has own IP address and belongs to one VLAN

Denoted by FA0/1.1, FA0/1.2 etc

Router passes traffic between sub-interfaces


Sub-interface setup

Router(config)#int fa port-number.subint-number

Router(config-if)#encapsulation dot1q vlan-no

Router(config-if)#ip address ip-address subnet-mask

CCNA 3 Week 9 VLAN Trunking. Copyright © 2005 University of Bolton Origins Dates back to radio and...

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