Ccna3mod9_VLAN Trunking Protocol

8/8/2019 Ccna3mod9_VLAN Trunking Protocol

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1Version 3.0

Module 9VLAN Trunking Protocol


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2Version 3.0

VLAN Communication

D evices on different VLANS must have arouter to communicate with each other If devices are on the same VLAN, then theycan communicate through a switch.


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3Version 3.0

Access Links

An access link is a link on the switch thatis a member of only one VLAN.This VLAN is referred to as the nativeVLAN of the port. Any device that is attached to the port is

completely unaware that a VLAN exists.


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4Version 3.0

Trunk Links

A trunk link is capable of supporting multipleVLANs.Trunk links are typically used to connect switches

to other switches or routers.Switches support trunk links on both FastEthernet and Gigabit Ethernet ports.Switches, routers, and some servers can beconnected to a VLAN trunk (NIC must supporttrunking)


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5Version 3.0

Access and Trunk Links


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6Version 3.0

Trunk Links

A trunk link does not belong to a specific VLAN. acts as a conduit for VLANs between switches and

routers.

The trunk link can be configured to transport allVLANs or to transport a limited number of VLANs.A trunk link may, however, may have a nativeVLAN. The native VLAN of the trunk is the VLAN that the

trunk uses if the trunk link fails for any reason.


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8Version 3.0

VLAN Identification

IS L - This protocol is a Cisco proprietaryencapsulati o n protocol for interconnectingmultiple switches; it is supported inswitches as well as routers.


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9Version 3.0

VLAN Identification

IEEE 802.1Q - This protocol is an IEEEstandard method for identifying VLANs byinserting a VLAN identifier into the frameheader. This process is referred to asframe tagging.


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10Version 3.0

2-by te TP ID

2-by te TC I

802.1q

S A and D AMACsMACs 80 2.1q Tag Type/LengthField

D ata (max 15 00bytes)

CRCNew CRC

NIC cards and networking devices can understand thisbaby giant frame (1522 bytes). However, a Cisco switchmust remove this encapsulation before sending the frameout on an access link.

Tag Protocol Identifier

Tag Control Info (includesVLAN ID )


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11Version 3.0

802.1q

A 4 -by te tag header containing a tag protocolidentifier (TP ID ) and tag control information (TC I) withthe following elements: A 2-by te TP ID with a fixed value of 0x8 100 . This value

indicates that the frame carries the 80 2.1Q /80 2.1p taginformation .

A TC I containing the following elements:Three -bit user priority

O ne -bit canonical format (CF I indicator)Tw elve-bit VLAN i d entifier (VID)-Uniquely i d entifies theVLAN t o w hich the frame bel o ngs

This VLAN I D is added to each frame to allowdelivery of frames across a switched trunk.


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12Version 3.0

Trunking

A trunk is a point-to-point link thatsupports several VLANsA trunk is used to save ports when creatinga link between two devices implementingVLANs


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13Version 3.0

Trunking


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14Version 3.0

Configuring Trunking

Fast Ethernet and Gigabit Ethernet trunkingmodes: On

Off D esirable Auto Non negotiate


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15Version 3.0


On - This mode puts the port into permanenttrunking mode. The port becomes a trunk porteven if the neighboring port does not agree to the

change.The on state does not allow for the negotiation of an encapsulation type. You must, therefore, specify the encapsulation in

the configuration


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16Version 3.0


O ff - This mode puts the port intopermanent nontrunking mode andnegotiates to convert the link into anontrunk link.The port becomes a nontrunk port even if the neighboring port does not agree to the

change.


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17Version 3.0


D esirable - This mode makes the portactively attempt to convert the link to atrunk link. The port becomes a trunk port if the neighboring port is set to on, desirable,or auto mode.


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18Version 3.0


Auto - This mode makes the port willing toconvert the link to a trunk link.The port becomes a trunk port if the neighboring

port is set to on or desirable mode.This is the default mode for all Ethernet ports. if the default setting is left on both sides of the

trunk link, the link will not become a trunk


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19Version 3.0


Non negotiate - This mode puts the portinto permanent trunking mode but preventsthe port from generating D ynamic TrunkingProtocol ( D TP) frames. You must configure the neighboring port

manually as a trunk port to establish a trunklink.


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20Version 3.0


For trunking to be auto negotiated on FastEthernet or Gigabit Ethernet ports, theports must be in the same VTP domain.However, you can use on or non negotiatemode to force a port to become a trunk,even if it is in a different domain.


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21Version 3.0


IOS-Based SwitchSwitch(config)# interface fastethernet 0

Switch(config-if)# switchport mode [access | multi | trunk]

Switch(config-if)# switchport trunk encapsulation {isl|dot1q}Switch(config-if)# switchport trunk allowed vlan remove vlan-list

Switch(config-if)# switchport trunk allowed vlan add vlan-list


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22Version 3.0

VLAN Trunking Protocol

VTP maintains VLAN configuration consistencyacross the entire network.VTP is a messaging protocol that uses Layer 2

trunk frames to manage the addition, deletion,and renaming of VLANs on a network-wide basis.Further, VTP allows you to make centralizedchanges that are communicated to all other

switches in the network.


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23Version 3.0

VTP Benefits


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24Version 3.0

VTP

All switches in the same management domainshare their VLAN information with each other, anda switch can participate in only one VTPmanagement domain.Switches in different domains do not share VTPinformation.Using VTP, switches advertise: Management domain Configuration revision number Known VLANs and their specific parameters


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25Version 3.0

VTP

Switches can be configured not to acceptVTP information.

These switches will forward VTPinformation on trunk ports in order toensure that other switches receive theupdate, but the switches will not modify

their database, nor will the switches sendout an update indicating a change in VLANstatus.


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26Version 3.0

VTP

By default, management domains are set toa non secure mode, meaning that theswitches interact without using apassword.Adding a password automatically sets themanagement domain to secure mode.

A password must be configured on everyswitch in the management domain to usesecure mode.


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27Version 3.0

VTP

The VTP database contains a revisionnumber.Each time a change is made, the switchincrements the revision number


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28Version 3.0

VTP

A higher configuration revision number indicates that the VLAN information that isbeing sent is more current then the stored copy.

Any time a switch receives an update that has ahigher configuration revision number, theswitch will overwrite the stored information withthe new information being sent in the VTP

update.That is why when adding a new switch, youshould make sure it has a lower revisionnumber than the others in the domain.


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29Version 3.0

VTP Modes

Switches can operate in any one of thefollowing three VTP modes: Server Client Transparent


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30Version 3.0

VTP Modes

S erver - If you configure the switch for server mode, you can create, modify, and delete VLANs,and specify other configuration parameters (suchas VTP version and VTP pruning) for the entireVTP domain.VTP servers: Advertise their VLAN configuration to other

switches in the same VTP domain

Synchronize the VLAN configuration with other switches based on advertisements received over trunk links.

This is the default mode on the switch.


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31Version 3.0

VTP Modes

C lient - VTP clients behave the same wayas VTP servers.However, you cannot add, change, or delete VLANs on a VTP client.

You can only adopt VLAN managementchanges


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32Version 3.0

VTP Modes

T ransparent - VTP transparent switches donot participate in VTP.

A V TP transparent s w itch do es n o t a d vertise its VLAN c o nfigurati o n , and doesnot synchronize its VLAN configurationbased on received advertisements. However, in VTP Version 2, transparent

switches do forward VTP advertisementsthat the switches receive out their trunkports.


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34Version 3.0

Configuring VTP

IOS-Based SwitchSwitch(vlan)# vtp domain dom ain-na me

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

Switch(vlan)# vtp password password

Switch(vlan)# vtp v2-mode (version2)


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35Version 3.0

Adding a Switch to an Existing D omainBe sure to reset the configurationrevision number of the new switchto be lower than the other switchesor VLAN info will be erased on theVTP Server and VTP Clients


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36Version 3.0

Inter-VLAN legacy routing

Re quires one 10Mbp s(prefera bly 100M bp s or 1 Gbp s) interface per VLAN .


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38Version 3.0

Trunking Provides Scalability

Using ISL or 801.Q,router only needsone port.

Note: this must be FastEthernet!

Subinterfaces areonly on the router for the VLANs


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39Version 3.0

External router config exampleRouter on a Stick


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40Version 3.0

External router config exampleRTA (config)# interface f0/0RTA (config-if)# no ip addressRTA (config-if)# interface f0/0.1RTA (config-subif)# encapsulation dot1q 1

RTA (config-subif)# ip address 10.1.1.1RTA (config-subif)# int f0/0.2RTA (config-subif)# encapsulation dot1q 20RTA (config-subif)# ip address 10.1.2.1RTA (config-subif)# int f0/0.3

RTA (config-subif)# encapsulation dot1q 30RTA (config-subif)# ip address 10.1.3.1


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41Version 3.0

Switch ConfigurationSwitch(config)# interface FastEthernet0/1Switch(config-if)# switchport mode trunkSwitch(config-if)# switchport trunk encapsulation

dot1q

Switch(config)# interface FastEthernet0/2Switch(config-if)# switchport access vlan 1

Switch(config)# interface FastEthernet0/3Switch(config-if)# switchport access vlan 10

Cant skip this step could beisl if using older equipment


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42Version 3 0

Module 9VLAN Trunking Protocol

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Ccna3mod9_VLAN Trunking Protocol