CCNA3 CHAPTER 4 VTP

CHAPTER 4
VTP
Introduction
As the size of the network for a small- or medium-sized business grows, the management involved
in maintaining the network grows. In the previous chapter, you learned how to create and manage
VLANs and trunks using Cisco IOS commands. The focus was on managing VLAN information
on a single switch. But what if you have many switches to manage? How will you manage the
VLAN database across many switches? In this chapter, you will explore how you can use the
VLAN Trunking Protocol (VTP) of Cisco Catalyst switches to simplify management of the VLAN
database across multiple switches.
4.1 VTP Concepts
4.1.1 What is VTP?
The VLAN Management Challenge
As the number of switches increases on a small- or medium-sized business network, the overall
administration required to manage VLANs and trunks in a network becomes a challenge.
Click Play to view an animation of the VLAN management challenge.
Small Network VLAN Management
In the animation, the figure shows a network manager adding a new VLAN, VLAN30. The network
manager needs to update the three trunks to allow VLANs 10, 20, 30, and 99. Recall that a
common error is forgetting to update the allowed list of VLANs on trunks.
Click the Larger Network button in the figure.
Larger Network VLAN Management
When you consider the larger network in the figure, the VLAN management challenge becomes
clear. After you have manually updated this network a few times, you may want to know if there is
a way for the switches to learn what the VLANs and trunks are so that you do not have to manually
configure them. You are ready to learn about VLAN trunking protocol (VTP).
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). Extendedrange
VLANs (IDs greater than 1005) are not supported by VTP.
Click Play in the figure to view an animation of an overview of how VTP works.
VTP Overview
96 CCNA Exploration Course Booklet: LAN Switching and Wireless, Version 4.0
VTP allows a network manager to makes changes on a switch that is configured as a VTP server.
Basically, 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.
Click the Two Switches button in the figure.
Two Switches
Click Play in the figure to view an animation on the basic VTP interaction between a VTP server
and a VTP client.
In the figure, a trunk link is added between switch S1, a VTP server, and S2, a VTP client. After a
trunk is established between the two 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. VTP advertisements will not be exchanged if the trunk
between the switches is inactive. The details on how VTP works is explained in the rest of this
chapter.
Benefits of VTP
You have learned that VTP maintains VLAN configuration consistency by managing the addition,
deletion, and renaming of VLANs across multiple Cisco switches in a network. VTP offers a number
of benefits for network managers, as shown in the figure.
VTP Components
There are number of key components that you need to be familiar with when learning about VTP.
Here is a brief description of the components, which will be further explained as you go through
the chapter.
■ 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- 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 Server- VTP servers advertise the VTP domain VLAN information to other VTPenabled
switches in the same VTP domain. VTP servers store the VLAN information for the
entire domain in NVRAM. The server is where VLANs can be 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.
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.
■ 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. Without
Chapter 4: VTP 97
VTP pruning, a switch floods broadcast, multicast, and unknown unicast traffic across all
trunk links within a VTP domain even though receiving switches might discard them.
Roll over the key VTP components in the figure to see where they are in the network.
4.2 VTP Operation
4.2.1 Default VTP Configuration
In CCNA Exploration: Network Fundamentals, you learned that a Cisco switch comes from the
factory with default settings. The default VTP settings are shown in the figure. The benefit of VTP
is that it automatically distributes and synchronizes domain and VLAN configurations across the
network. However, this benefit comes with a cost, you can only add switches that are in their default
VTP configuration. If you add a VTP-enabled switch that is configured with settings that supersede
existing network VTP configurations, changes that are difficult to fix are automatically
propagated throughout the network. So make sure that you only add switches that are in their default
VTP configuration.You will learn how to add switches to a VTP network later in this chapter.
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 discussion
of VTP versions is beyond the scope of this course.
Click the Switch Output button in the figure to see the default VTP settings on switch S1.
Displaying the VTP Status
The figure shows how to view the VTP settings for a Cisco 2960 switch, S1. The Cisco IOS command
show VTP status displays the VTP status. The output shows that switch S1 is in VTP server
mode by default and that there is no VTP domain name assigned. The output also shows that the
maximum VTP version available for the switch is version 2, and that VTP version 2 is disabled.
You will use the show VTP status command frequently as you configure and manage VTP on a
network. The following briefly describes the show VTP status parameters:
■ 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.
98 CCNA Exploration Course Booklet: LAN Switching and Wireless, Version 4.0
■ 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.
4.2.2 VTP Domains
VTP Domains
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. The figure shows a
network with two VTP domains, cisco2 and cisco3. In this chapter, the three switches, S1, S2, and
S3, will be configured for VTP.
A VTP domain consists of one switch or several interconnected switches sharing the same VTP
domain name. Later in this chapter, you will learn how VTP-enabled switches acquire a common
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.
Click the Switch Output button in the figure to see switch S4 output.
VTP Domain Name Propagation
For a VTP server or client switch to participate in a VTP-enabled network, it must be a part of the
same domain. 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.
Click Play in the figure to see how a VTP server propagates the VTP domain name in a network.
The network in the figure shows three switches, S1, S2, and S3, in their default VTP configuration.
They are configured as VTP servers. VTP domain names have not been configured on any of the
switches.
The network manager configures the VTP domain name as cisco1 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 server switches update their VTP configuration to the new domain name.
Note: Cisco recommends that access to the domain name configuration functions be protected by
a password. The details of password configuration will be presented later in the course.
How does the domain name get placed into a VTP advertisement? What information is exchanged
between VTP-enabled switches? In the next topic, you will learn about the details of VTP advertisements
and find answers to these questions.
4.2.3 VTP Advertising
VTP Frame Structure
VTP advertisements (or messages) distribute VTP domain name and VLAN configuration changes
to VTP-enabled switches. In this topic, you will learn about the VTP frame structure and how the
three types of advertisements enable VTP to distribute and synchronize VLAN configurations
throughout the network.
Click the Overview button in the figure and then click Play to view an animation on the structure
of a VTP frame.
VTP Frame Encapsulation
Chapter 4: VTP 99
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.
Click the VTP Frame Details button in the figure.
VTP Frame Details
In the figure, you can see the VTP frame structure in more detail. Keep in mind that a VTP frame
encapsulated as an 802.1Q frame is not static. The contents of the VTP message determines which
fields are present. The receiving VTP-enabled switch looks for specific fields and values in the
802.1Q frame to know what to process. The following key fields are present when a VTP frame is
encapsulated as an 802.1Q frame:
Destination MAC address- This address is set to 01-00-0C-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.
SNAP field- Subnetwork Access Protocol (SNAP) field has an OUI set to AAAA and type set to
2003.
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 field- Varies depending on the message type.
Click the VTP Message Contents button in the figure.
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
100 CCNA Exploration Course Booklet: LAN Switching and Wireless, Version 4.0
■ 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.
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.
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. The figure
shows a network manager adding three VLANs to switch S1.
Click the Switch Output button in the figure to see how the revision number has been changed.
The highlighted area shows that the revision number on switch S1 is 3, the number of VLANs is
up to eight, because three VLANs have been added to the five default VLANs.
The revision number plays an important and complex role in enabling VTP to distribute and synchronize
VTP domain and VLAN configuration information. To comprehend what the revision
number does, you first need to learn about the three types of VTP advertisements and the three
VTP modes.
VTP Advertisements
Summary Advertisements
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
Click the Summary button in the figure and then click Play to view an animation on the summary
VTP advertisements.
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
It may take multiple subset advertisements to fully update the VLAN information.
Chapter 4: VTP 101
Click the Subset button in the figure and then click Play to view an animation on the subset
VTP advertisements.
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
Click the Request button in the figure and then click Play to view an animation on the request
VTP advertisements.
VTP Advertisements Details
VTP uses advertisements to distribute and synchronize information about domains and VLAN
configurations. There are three main VTP advertisements.
Each type of VTP advertisement sends information about several parameters used by VTP. A description
of the fields in each of the VTP advertisements are presented.
Click the Summary Details button in the figure.
Summary Advertisements
Summary advertisements comprise the majority of VTP advertisement traffic. Roll over the fields
in the summary advertisement to view the descriptions.
Roll over the fields in the summary advertisement to view the descriptions.
Click the Subset Details button in the figure.
Subset Advertisements
The fields found in a subset advertisement are briefly described. The fields in the VLAN-info are
not described.
Roll over the fields in the subset advertisement to view the descriptions.
Click the Request Details button in the figure.
Request Advertisements
The fields found in a request advertisement are briefly described.
Roll over the fields in the request advertisement to view the descriptions.
4.2.4 VTP Modes
VTP Modes Overview
A Cisco switch, configured with Cisco IOS software, can be configured in either server, client, or
transparent mode. These modes differ in how they are used to manage and advertise VTP domains
and VLANs.
Server Mode
102 CCNA Exploration Course Booklet: LAN Switching and Wireless, Version 4.0
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.
Client Mode
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. Often
there are many network administrators working at different times of the day. Having only a few
switches that are physically able to maintain VLAN configurations makes it easier to control
VLAN upgrades and to track which network administrators performed them.
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. A cost-conscious network administrator could choose to configure a few wellequipped
switches as VTP servers, and then use switches with less memory as VTP clients. Although
a discussion of network redundancy is beyond the scope of this course, know that the
number of VTP servers should be chosen to provide the degree of redundancy that is desired in the
network.
Transparent Mode
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.
VTP in Action
You will now see how the various VTP features come together to distribute and synchronize domain
and VLAN configurations in a VTP-enabled network. The animation starts with three new
switches, S1, S2, and S3, configured with their factory default settings, and finishes with all three
switches configured and participating in a VTP-enabled network.
You can pause and rewind the animation to reflect and review this process.
You have seen how VTP works with three switches. This animation examines in more detail how a
switch configured in VTP transparent mode supports the functionality of VTP.
Chapter 4: VTP 103
Click the Play button in the figure.
You can pause and rewind the animation to reflect and review this process.
4.2.5 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. You need to enable pruning on only one VTP server switch in the
domain. In the figure, you would enable VTP pruning on switch S1. The figure shows a network
with VLAN 10 and VLAN 20 configured. Switch S3 has VLAN 20 configured, and switch S2 has
VLAN 10 and VLAN 20 configured. Examine the topology in the figure and then click to see the
switch configurations.
VTP Pruning in Action
Recall that a VLAN creates an isolated broadcast domain. A switch floods broadcast, multicast,
and unknown unicast traffic across all trunk links within a VTP domain. When a computer or device
broadcasts on a VLAN, for example, VLAN 10 in the figure, the broadcast traffic travels
across all trunk links throughout the network to all ports on all switches in VLAN 10. In the figure,
switches S1, S2, and S3 all receive broadcast frames from computer PC1. The broadcast traffic
from PC1 consumes bandwidth on the trunk link between all 3 switches and consumes processor
time on all 3 switches. The link between switches S1 and S3 does not carry any VLAN 10 traffic,
so it is a candidate for VTP pruning.
Click the Play button in the figure to see the how VLAN flood traffic is handled on a network
with no VTP pruning.
VTP Pruning
Click the VTP Pruning button and then click Play to see an animation on how VLAN flood
traffic is handled on a network with VTP pruning.
The flood traffic is stopped from entering the trunk connecting switches S1 and S2. VTP pruning
only prunes the egress port F0/1 on switch S2.
VTP Pruning Enabled
The figure shows a network topology that has switches S1, S2, and S3 configured with VTP pruning.
When VTP pruning is enabled on a network, it reconfigures the trunk links based on which
ports are configured with which VLANs.
Click the Switch S1 button in the figure.
The highlighted area shows that the trunk on port F0/1 allows VLAN 10 traffic. VTP pruning only
prunes the egress port.
Click the Switch S2 button in the figure.
The highlighted area shows that the trunk on port F0/1 does not allow VLAN 10 traffic. VLAN 10
is not listed. For more details on VTP pruning, visit: http://www.cisco.com/univercd/cc/td/doc/
product/lan/cat5000/rel_4_2/config/vlans.htm#xtocid798016.
4.3 Configure VTP
104 CCNA Exploration Course Booklet: LAN Switching and Wireless, Version 4.0
4.3.1 Configuring VTP
VTP Configuration Guidelines
Now that you are familiar with the functionality of VTP, you are ready to learn how to configure a
Cisco Catalyst switch to use VTP. The topology shows the reference topology for this chapter.
VTP will be configured on this topology.
Click the Table button in the figure.
VTP Server Switches
Follow these steps and associated guidelines to ensure that you configure VTP successfully:
■ Confirm that all of the switches you are going to configure have been set to their default
settings.
■ Always reset the configuration revision number before installing a previously configured
switch into a VTP domain. Not resetting the configuration revision number allows for potential
disruption in the VLAN configuration across the rest of the switches in the VTP domain.
■ Configure at least two VTP server switches in your network. Because only server switches can
create, delete, and modify VLANs, you should make sure that you have one backup VTP
server in case the primary VTP server becomes disabled. If all the switches in the network are
configured in VTP client mode, you cannot create new VLANs on the network.
■ Configure a VTP domain on the VTP server. Configuring the VTP domain on the first switch
enables VTP to start advertising VLAN information. Other switches connected through trunk
links receive the VTP domain information automatically through VTP advertisements.
■ If there is an existing VTP domain, make sure that you match the name exactly. VTP domain
names are case-sensitive.
■ If you are configuring a VTP password, ensure that the same password is set on all switches in
the domain that need to be able to exchange VTP information. Switches without a password
or with the wrong password reject VTP advertisements.
■ Ensure that all switches are configured to use the same VTP protocol version. VTP version 1
is not compatible with VTP version 2. By default, Cisco Catalyst 2960 switches run version 1
but are capable of running version 2. When the VTP version is set to version 2, all version 2
capable switches in the domain autoconfigure to use version 2 through the VTP
announcement process. Any version 1-only switches cannot participate in the VTP domain
after that point.
■ Create the VLAN after you have enabled VTP on the VTP server. VLANs created before you
enable VTP are removed. Always ensure that trunk ports are configured to interconnect
switches in a VTP domain. VTP information is only exchanged on trunk ports.
VTP Client Switches
■ As on the VTP server switch, confirm that the default settings are present.
■ Configure VTP client mode. Recall that the switch is not in VTP client mode by default. You
have to configure this mode.
■ Configure trunks. VTP works over trunk links.
■ Connect to a VTP server. When you connect to a VTP server or another VTP-enabled switch,
it takes a few moments for the various advertisements to make their way back and forth to the
VTP server.
Chapter 4: VTP 105
■ Verify VTP status. Before you begin configuring the access ports, confirm that the revision
mode and number of VLANs have been updated.
■ Configure access ports. When a switch is in VTP client mode, you cannot add new VLANs.
You can only assign access ports to existing VLANs.
Configuring VTP Step 1 – Configure the VTP Server
The next three topics will show you how to configure a VTP server and two VTP clients. Initially
none of the devices are connected.
The topology highlights switch S1. You will configure this switch to be a VTP server. The commands
to configure the trunk ports are provided for interface F0/1.
Click the Confirm Details button in the figure.
The output of the show vtp status command confirms that the switch is by default a VTP server.
Since no VLANs have yet been configured, the revision number is still set to 0 and the switch does
not belong to VTP domain.
If the switch was not already configured as a VTP server, you could configure it using the the vtp
mode {server} command.
Click the Configure Domain Name button in the figure.
The domain name is configured using the the vtp domain domain-name command. In the figure,
switch S1 has been configured with the domain name cisco1.
For security reasons, a password could be configured using the vtp password password command.
Click the Configure Version button in the figure.
Most switches can support VTP version 1 and 2. However, the default setting for Catalyst 2960
switches is version 1. When the vtp version 1 command is entered on the switch, it informs us
that the switch is already configured to be in version 1.
Click the Add VLANs and Trunks button in the figure.
Assume that three VLANs have been configured and have been assigned VLANs names. The output
in the figure is displaying the result of these changes.
You can use the no version of the commands.
The topology highlights switches S2 and S3. You will be shown the VTP client configuration for
S2. To configure S3 as a VTP client, you will follow the same procedure.
Click the Confirm Defaults button to verify the switch status.
Before configuring a switch as a VTP client, verify its current VTP status. Once you’ve confirmed
status, you will configure the switch to operate in VTP client mode.
Click the Enable VTP Client Mode button to see how to configure a switch for VTP client mode.
Configure VTP client mode using the following Cisco IOS command syntax:
Enter global configuration mode with the configure terminal command.
Configure the switch in client mode with the vtp mode {client} command.
If you need to reset the VTP configuration to the default values, you can use the no version of the
commands.
Click the Verify VTP Status button to see the rest of VTP client configuration.
Configuring VTP Step 3 – Confirm and Connect
106 CCNA Exploration Course Booklet: LAN Switching and Wireless, Version 4.0
After configuring the main VTP server and the VTP clients, you will connect the VTP client
switch S2 to the switch S1 VTP server.
The topology highlights the trunks that will be added to this topology. In the figure, switch S2 will
be connected to switch S1. Then switch S2 will be configured to support the computers, PC1 to PC3.
The same procedure will be applied to switch S3, although the commands for S3 are not shown.
Confirm VTP Operation
Click the Confirm VTP Operation button in the figure.
There are two Cisco IOS commands for confirming that VTP domain and VLAN configurations
have been transferred to switch S2. Use the show VTP status command to verify the following:
■ Configuration revision number has been incremented to 6.
■ There are now three new VLANs indicated by the existing number of VLANs showing 8.
■ Domain name has been changed to cisco1.
Use the show vtp counters command to confirm that the advertisements took place.
Configure Access Ports
Click the Configure Access Ports button in the figure.
The top highlight in the screen output confirms that the switch S2 is in VTP client mode. The task
now is to configure the port F0/18 on switch S2 to be in VLAN 20. The bottom highlighted area
shows the Cisco IOS command used to configure port F0/18 on switch S2 to be in VLAN 20.
4.3.2 Troubleshooting VTP Configurations
Troubleshooting VTP Connections
You have learned how VTP can be used to simplify managing a VLAN database across multiple
switches. In this topic, you will learn about common VTP configuration problems. This information,
combined with your VTP configuration skills, will help you when troubleshooting VTP configuration
problems.
The figure lists the common VTP configuration issues that will be explored in this topic.
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. However, older switches may only support
VTP version 1. Switches that only support version 1 cannot participate in the VTP domain
along with version 2 switches. If your network contains switches that support only version 1, you
need to manually configure the version 2 switches to operate in version 1 mode.
Click the VTP Version Solution button in the figure.
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. Forgetting to set a VTP password is a very
common problem. If a password is used, it must be configured on each switch in the domain. By
default, a Cisco switch does not use a VTP password. The switch does not automatically set the
password parameter, unlike other parameters that are set automatically when a VTP advertisement
is received.
Click the VTP Password Solution button in the figure.
Chapter 4: VTP 107
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. As you learned earlier, if a switch receives
the wrong VTP advertisement, the switch discards the message. If the discarded message
contains legitimate configuration information, the switch does not synchronize its VLAN database
as expected.
Click Play in the figure to see an animation of this issue.
Click the VTP Domain Solution button in the figure.
Solution
To avoid incorrectly configuring a VTP domain name, only set the VTP domain name on one VTP
server switch. All other switches in the same VTP domain will accept and automatically configure
their VTP domain name when they receive the first VTP summary advertisement.
Switches Set to VTP Client Mode
It is possible to change the operating mode of all switches to VTP client. By doing so, you lose all
ability to create, delete, and manage VLANs within your network environment. Because the VTP
client switches do not store the VLAN information in NVRAM, they need to refresh the VLAN information
after a reload.
Click Play in the figure to see an animation of this issue.
Click the Solution button in the figure.
Solution
To avoid losing all VLAN configurations in a VTP domain by accidentally reconfiguring the only
VTP server in the domain as a VTP client, you can configure a second switch in the same domain
as a VTP server. It is not uncommon for small networks that use VTP to have all the switches in
VTP server mode. If the network is being managed by a couple of network administrators, it is unlikely
that conflicting VLAN configurations will arise.
Incorrect Revision Number
Even after you have configured the switches in your VTP domain correctly, there are other factors
that can adversely affect the functionality of VTP.
Configuration Revision Number Issues
The topology in the figure is configured with VTP. There is one VTP server switch, S1, and two
VTP client switches, S2 and S3.
Click the Incorrect Revision Number button in the figure to play an animation showing how
the addition of a switch with a higher configuration revision number affects the rest of the switches
in the 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 the existing
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
108 CCNA Exploration Course Booklet: LAN Switching and Wireless, Version 4.0
in switch S4. As each switch reconfigures itself with VLANs that are not supported in the network,
the ports no longer forward traffic from the computers because they are configured with VLANs
that no longer exist on the newly reconfigured switches.
Click the Reset Revision Number button in the figure.
Solution
The solution to the problem is to reset each switch back to an earlier configuration and then reconfigure
the correct VLANs, 10 and 20, on switch S1. To prevent this problem in the first place, reset
the configuration revision number on previously configured switches being added to a VTP-enabled
network. The figure shows the commands needed to reset switch S4 back to the default revision
number.
Click Verify Revision Number button in the figure to see that switch S4 has had its revision
number reset.
4.3.3 Managing VLANs on a VTP Server
Managing VLANs on a VTP Server
You have learned about VTP and how it can be used to simplify managing VLANs in a VTP-enabled
network. Consider the topology in the figure. 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.
Click the Configure New VLANs and Ports button in the figure.
The figure displays the commands used to configure VLAN 10 and the port F0/11 on switch S1.
The commands to configure the correct ports for switches S2 and S3 are not shown.
After you have configured the new VLAN on switch S1 and configured the ports on switches S1,
S2, and S3 to support the new VLAN, confirm that VTP updated the VLAN database on switches
S2 and S3.
Click the show vtp status button in the figure.
The output of the command is used to verify the configuration on switch S2. The verification for
S3 is not shown.
Click the show interfaces trunk button in the figure.
The output confirms that the new VLAN has been added to F0/1 on switch S2. The highlighted
area shows that VLAN 10 is now active in the VTP management domain.
In this activity, you will practice configuring VTP. When Packet Tracer first opens, the switches already
contain a partial configuration.
Detailed instructions are provided within the activity as well as in the PDF link below.
Activity Instructions (PDF)
Refer to Packet
Tracer Activity
for this chapter
Chapter 4: VTP 109
4.4 Chapter Labs
4.4.1 Basic VTP Configuration
Imagine a network with 50 switches with a total of 12 identical VLANs each. If you had to manually
type in the commands to each switch, it would be a huge undertaking. It would be so much
easier if you could configure those 12 VLANs once, and then allow those VLANs to be propagated
automatically to the other 49 switches. VTP configuration makes this possible.
This activity is a variation of Lab 4.4.1. Packet Tracer may not support all the tasks specified in the
hands-on lab. This activity should not be considered equivalent to completing the hands-on lab.
Packet Tracer is not a substitute for a hands-on lab experience with real equipment.
Detailed instructions are provided within the activity as well as in the PDF link below.
Activity Instructions (PDF)
4.4.2 VTP Configuration Challenge
How much of the basics of VTP configuration do you remember? Let’s see how much you can
configure from memory having completed the Basic VTP lab. Be sure to check your work with the
answer key that your instructor will provide.
This activity is a variation of Lab 4.4.2. Packet Tracer may not support all the tasks specified in the
hands-on lab. This activity should not be considered equivalent to completing the hands-on lab.
Packet Tracer is not a substitute for a hands-on lab experience with real equipment.
Detailed instructions are provided within the activity as well as in the PDF link below.
Activity Instructions (PDF)
4.4.3 Troubleshooting VTP Configuration
In this lab, you will use the supplied scripts to configure S1 as a VTP server, and S2 and S3 as
VTP clients. However, there are a number of errors in this configuration that you must troubleshoot
and correct before end-to-end connectivity within the VLAN is restored.
You will have successfully resolved all errors when the same VLANs are configured on all three
switches, and you can ping between any two hosts in the same VLAN or between any two
switches.
This activity is a variation of Lab 4.4.3. Packet Tracer may not support all the tasks specified in the
hands-on lab. This activity should not be considered equivalent to completing the hands-on lab.
Packet Tracer is not a substitute for a hands-on lab experience with real equipment.
Detailed instructions are provided within the activity as well as in the PDF link below.
Activity Instructions (PDF)
Refer to
Lab Activity
for this chapter
Refer to Packet
Tracer Activity
for this chapter
Refer to
Lab Activity
for this chapter
Refer to Packet
Tracer Activity
for this chapter
Refer to
Lab Activity
for this chapter
Refer to Packet
Tracer Activity
for this chapter
110 CCNA Exploration Course Booklet: LAN Switching and Wireless, Version 4.0
Chapter Summary
In this chapter, we discussed the VLAN trunking protocol. VTP is a Cisco-proprietary protocol
used to exchange VLAN information across trunk links, reducing VLAN administration and configuration
errors. VTP allows you to create a VLAN once within a VTP domain and have that
VLAN propagated to all other switches in the VTP domain.
There are three VTP operating modes: server, client, and transparent. VTP client mode switches
are more prevalent in large networks, where there definition reduces the administration of VLAN
information. In small networks, network managers can more easily keep track of network changes,
so switches are often left in the default VTP server mode.
VTP pruning limits the unnecessary propagation of VLAN traffic across a LAN. VTP determines
which trunk ports forward which VLAN traffic. VTP pruning improves overall network performance
by restricting the unnecessary flooding of traffic across trunk links. Pruning only permits
VLAN traffic for VLANs that are assigned to some switch port of a switch on the other end of a
trunk link. By reducing the total amount of flooded traffic on the network, bandwidth is freed up
for other network traffic.
We discussed VTP configuration and preventative measures to take to avoid common problematic
VTP issues.
In this activity, you will configure switches including basic configuration, port security, trunking
and VLANs. You will use VTP to advertise the VLAN configurations to other switches.
Activity Instructions (PDF)
Chapter Quiz
Take the chapter quiz to test your knowledge.
Refer to Packet
Tracer Activity
for this chapter

About these ads
This entry was posted in Uncategorized. Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s