1. Chap 4 – Implement VTP Learning Objectives
Explain the role of VTP in a converged switched network
Describe the operation of VTP: VTP domains, VTP Modes, VTP Advertisements, and VTP Pruning.
Configure VTP on the switches in a converged network.

2. VLAN Trunking Protocol (VTP)
Before discussing VTP, it is important to understand that VTP is
not necessary in order to configure VLANs or Trunking on Cisco
Switches.
VTP is a Cisco proprietary protocol that allows VLAN configuration to be consistently maintained across a common administrative domain.
VTP minimises the possible configuration inconsistencies that arise when changes are made.
Additionally, VTP reduces the complexity of managing and monitoring VLAN networks, allowing changes on one switch to be propagated to other switches via VTP.
On most Cisco switches, VTP is running and has certain defaults already configured.
VLAN Trunking Protocol (VTP) was created by Cisco to solve operational problems in a switched network with VLANs. It is a Cisco proprietary protocol.
As an organisation grows and additional switches are added to the network, each new switch must be manually configured with VLAN information. A single incorrect VLAN assignment could cause two potential problems:
Cross-connected VLANs due to VLAN configuration inconsistencies
VLAN misconfiguration across mixed media environments such as Ethernet and Fiber Distributed Data Interface (FDDI)
With VTP, VLAN configuration is consistently maintained across a common administrative domain. Additionally, VTP reduces management and monitoring complexities of networks with VLANs

3. VTP stores VLAN configurations in the VLAN database called vlan.dat.
VTP Operation
1. Create VLAN 40 on S1 – VTP server
VTP allows a network manager to makes changes on a switch that is configured as a VTP server. The VTP server distributes and synchronizes VLAN information to VTP-enabled switches throughout the switched network, S1
VLAN 40
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Fa0/1
Fa0/2
Fa0/11
Fa0/11 S2 S3
Fa0/1
Fa0/2
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Fa0/18
Fa0/18
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Fa0/6
VLAN 40
Fa0/6
VTP allows a network manager to makes changes on a switch that is configured as a VTP server. The VTP server distributes and synchronizes VLAN information to VTP-enabled switches throughout the switched network, which minimizes the problems caused by incorrect configurations and configuration inconsistencies. VTP stores VLAN configurations in the VLAN database called vlan.dat.
After a trunk is established between switches, VTP advertisements are exchanged between the switches. Both the server and client leverage advertisements from one another to ensure each has an accurate record of VLAN information.
2. VTP propagates VLAN 40 to S2 & S3 – VTP clients
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VTP stores VLAN configurations in the VLAN database called vlan.dat.

4. VTP Components
VTP Domain - consists of one or more interconnected switches. All switches in a domain share VLAN configuration details using VTP advertisements. A router or Layer 3 switch defines the boundary of each domain.
VTP Advertisements - used 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 Server - store the VLAN information for the entire domain in NVRAM. The server is where VLAN can created, deleted, or renamed for the domain.
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.
VTP Transparent - forwards VTP advertisements to VTP clients and VTP servers, but do not participate in VTP. VLANs that are created, renamed, or deleted on transparent switches are local to that switch only.
VTP Pruning - VTP pruning increases network available bandwidth by restricting flooded traffic to those trunk links that the traffic must use to reach the destination devices.

5. Default VTP Configuration
Sh vtp status
VTP Version - Displays the VTP version the switch is capable of running. By default, the switch implements version 1, but can be set to version 2.
Configuration Revision - Current configuration revision number on this switch. You will learn more about revisions numbers in this chapter.
Maximum VLANs Supported Locally - Maximum number of VLANs supported locally.
Number of Existing VLANs - Number of existing VLANs.
VTP Operating Mode - Can be server, client, or transparent.
VTP Domain Name - Name that identifies the administrative domain for the switch.
VTP Pruning Mode - Displays whether pruning is enabled or disabled.
VTP V2 Mode - Displays if VTP version 2 mode is enabled. VTP version 2 is disabled by default.
VTP Traps Generation - Displays whether VTP traps are sent to a network management station.
MD5 Digest - A 16-byte checksum of the VTP configuration.
Configuration Last Modified-Date and time of the last configuration modification. Displays the IP address of the switch that caused the configuration change to the database.

6. VTP Domains
VTP allows separation of a network into smaller management domains to help reduce VLAN management S1 S2 S3
cisco1
cisco2
Until the VTP domain name is specified, VLANs cannot be created or modified on a VTP server, and VLAN information is not propagated over the network. S4 S5 S6
VTP allows you to separate your network into smaller management domains to help reduce VLAN management. An additional benefit of configuring VTP domains is that it limits the extent to which configuration changes are propagated in the network if an error occurs.
A VTP domain consists of one switch or several interconnected switches sharing the same VTP domain name.
A switch can be a member of only one VTP domain at a time.
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.

7. VTP Domain Name Propagation
The network manager configures the VTP domain name as cisco2 on the VTP server switch S1.
The VTP server sends out a VTP advertisement with the new domain name embedded inside.
The S2 and S3 VTP client switches update their VTP configuration to the new domain name.
cisco2 S1
Server
Null0
cisco2
VTP
Advert
VTP
Advert S2 S3
Client
Client
Null0
Null0
cisco2
cisco2

8. VTP Frame Structure
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.
Destination MAC address-This address is set to C-CC-CC-CC, which is the reserved multicast address for all VTP messages.
LLC field-Logical link control (LLC) field contains a destination service access point (DSAP) and a source service access point (SSAP) set to the value of AA.
VTP header field- The contents vary depending on the VTP message type-summary, subset, or request-but it always contains these VTP fields:
Domain name- Identifies the administrative domain for the switch.
Domain name length- Length of the domain name.
Version- Set to either VTP 1, VTP 2, or VTP 3. The Cisco 2960 switch only supports VTP 1 and VTP 2.
Configuration revision number- The current configuration revision number on this switch.
VTP Message Contents. 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

9. VTP Revision Number
The configuration revision number is a 32-bit number that indicates the level of revision for a VTP frame.
The default configuration number for a switch is zero.
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.

10. VTP Message Types
Server and client switches issue summary advertisements every 5 minutes. Servers inform neighbor switches what they believe to be the current VTP revision number
The summary advertisement contains the VTP domain name, the current revision number, and other VTP configuration details. Summary advertisements are sent:
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
Immediately after a configuration has been made
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
It may take multiple subset advertisements to fully update the VLAN information.
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
Clients request VLAN information from servers using the advertisement request.
Subset advertisements contain detailed information about VLANs and are sent by servers in response to an advertisement request from a client.

11. VTP Operation - Server
VTP servers can create, modify, delete VLAN and VLAN configuration parameters for the entire domain.
VTP servers save VLAN configuration information in the switch NVRAM.
VTP servers send VTP messages out to all trunk ports.
In server mode, you can create, modify, and delete VLANs for the entire VTP domain. VTP server mode is the default mode for a Cisco switch.
VTP servers advertise their VLAN configurations to other switches in the same VTP domain and synchronize their VLAN configurations with other switches based on advertisements received over trunk links.
VTP servers keep track of updates through a configuration revision number.
Other switches in the same VTP domain compare their configuration revision number with the revision number received from a VTP server to see if they need to synchronize their VLAN database.

12. VTP Operation - Client
VTP clients cannot create, modify, or delete VLAN information.
The only role of VTP clients is to process VLAN changes and send VTP messages out all trunk ports.
The VTP client maintains a full list of all VLANs within the VTP domain, but it does not store the information in NVRAM.
Any changes made must be received from a VTP server advertisement.
If a switch is in client mode, you cannot create, change, or delete VLANs. In addition, the VLAN configuration information that a VTP client switch receives from a VTP server switch is stored in a VLAN database, not in NVRAM. Consequently, VTP clients require less memory than VTP servers. When a VTP client is shut down and restarted, it sends a request advertisement to a VTP server for updated VLAN configuration information.
Switches configured as VTP clients are more typically found in larger networks, because in a network consisting of many hundreds of switches, it is harder to coordinate network upgrades.
For large networks, having client switches is also more cost-effective. By default, all switches are configured to be VTP servers. This configuration is suitable for small scale networks in which the size of the VLAN information is small and the information is easily stored in NVRAM on the switches. In a large network of many hundreds of switches, the network administrator must decide if the cost of purchasing switches with enough NVRAM to store the duplicate VLAN information is too much.

13. VTP Operation - Transparent
Switches in VTP transparent mode forward VTP advertisements but ignore information contained in the message.
A transparent switch will not modify its database when updates are received, nor will the switch send out an update indicating a change in its own VLAN status.
Except for forwarding VTP advertisements, VTP is disabled on a transparent switch.
There is also an “off” VTP mode in which switches behave the same as in the VTP transparent mode, except VTP advertisements are not forwarded.
Switches configured in transparent mode forward VTP advertisements that they receive on trunk ports to other switches in the network.
VTP transparent mode switches do not advertise their VLAN configuration and do not synchronize their VLAN configuration with any other switch. Configure a switch in VTP transparent mode when you have VLAN configurations that have local significance and should not be shared with the rest of the network.
In transparent mode, VLAN configurations are saved in NVRAM (but not advertised to other switches), so the configuration is available after a switch reload. This means that when a VTP transparent mode switch reboots, it does not revert to a default VTP server mode, but remains in VTP transparent mode.

14. VTP Pruning
VTP pruning prevents unnecessary flooding of broadcast information from one VLAN across all trunks in a VTP domain.
VTP pruning permits switches to negotiate which VLANs are assigned to ports at the other end of a trunk and, hence, prune the VLANs that are not assigned to ports on the remote switch.
Pruning is disabled by default. VTP pruning is enabled using the vtp pruning global configuration command on the VTP Server. S1
PC1
VLAN 10
PC4
VLAN 20
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Without VTP pruning, a broadcast for VLAN 10 on S2 will propagate across the trunks to S3, which has no PCs in VLAN 10.
S3 will not propagate the broadcast, but valuable trunk bandwidth is wasted. S2 S3
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PC2
VLAN 20
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PC5
VLAN 20
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PC3
VLAN 10
PC6
VLAN 20

15. S2 will no longer send VLAN 10 broadcasts out of Fa0/1
VTP Pruning Enabled
S2 will no longer send VLAN 10 broadcasts out of Fa0/1 S1
PC1
VLAN 10
PC4
VLAN 20
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VLAN 10
PC6
VLAN 20

16. VTP Server Configuration
1. Check VTP revision number, mode, domain name
(Use reset vtp command to zeroise revision number)
Server S1
PC1
VLAN 10
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Fa0/11
Note – if you plug a switch into an existing network that has previously been configured as a server, there is a possibility that its revision number may be higher than the server already in the network – thus it will update all the clients/servers in the network with its configuraton, which will overwrite the required vlan configuration.
Therefore:
Always check the VTP revision number, before connecting the trunk link.
Always zeroise the VTP counters on a new switch. S2
Fa0/1
Fa0/2
PC2
VLAN 20
Fa0/18
2. Use vtp domain command to configure domain name as ‘cisco1’
Fa0/6
Client
PC3
VLAN 30

17. VTP Server Configuration
3. Use vtp version command to set VTP version
(VTP 1 and VTP are not compatible)
Server S1
PC1
VLAN 10
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Fa0/11 S2
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PC2
VLAN 20
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Client
4. Add VLANs, activate Fa0/1 trunk
PC3
VLAN 30

18. VTP Client Configuration
1. Check VTP revision number, mode, domain name
(Use reset vtp command to zeroise revision number)
Server S1
PC1
VLAN 10
Fa0/1
Fa0/11
Note: The VTP domain name can be learned by a client switch from a server switch, but only if the client switch domain is in the null state.
It does not learn a new name if one has been previously set.
For that reason, it is good practice to manually configure the domain name on all switches to ensure that the domain name is configured correctly. Switches in different VTP domains do not exchange VLAN information. S2
Fa0/1
Fa0/2
PC2
VLAN 20
Fa0/18
2. Use vtp mode client command to configure S2 as a client
Fa0/6
Client
PC3
VLAN 30

19. VTP Client Configuration
3. Check status of trunk and VTP parameters
Server S1
PC1
VLAN 10
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Fa0/11 S2
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Fa0/2
PC2
VLAN 20
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Client
3. Connect trunk cabling,
Check VTP advertisements being exchanged
PC3
VLAN 30

20. Troubleshooting VTP
Incompatible VTP Versions - VTP versions 1 and 2 are incompatible with each other. Modern Cisco Catalyst switches, such as the 2960, are configured to use VTP version 1 by default.
VTP Password Issues - When using a VTP password to control participation in the VTP domain, ensure that the password is set correctly on all switches in the VTP domain.
Incorrect VTP Domain Name - The VTP domain name is a key parameter that is set on a switch. An improperly configured VTP domain affects VLAN synchronization between switches. To avoid incorrectly configuring a VTP domain name, only set the VTP domain name on one VTP server switch.
All Switches Set to VTP Client Mode - lose all ability to create, delete, and manage VLANs within a network. To avoid losing all VLAN configurations in a VTP domain, configure a second switch in the same domain as a VTP server.

21. Any
Questions?

22. Chapter 4.4.1 – Basic VTP Config
Lab Topology
Chapter – Basic VTP Config S1
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Broadcast traffic has been minimised on the network shown, by creating 3 separate VLANs. All broadcast traffic created in VLAN20 is only pseen by devices that are part of VLAN20.
To exchange information between different VLANs, it is necessary to use a router to perform layer 3 switching. In effect, each VLAN uses the router as a default gateway to reach other VLANs.