VLAN Trunking Protocol

VTP
 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.
 What is VTP? Small Network VLAN Management
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 becomes a
challenge.
Small Network VLAN Management
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. Larger Network VLAN Management
Recall that a common error is forgetting to
update the allowed list of VLANs on trunks.
Larger Network VLAN Management
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.
VLAN trunking protocol (VTP).
 What is 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.
Switch can be configured a VTP server or VTP
client.
VTP only learns about normal-range VLANs
(VLAN IDs 1 to 1005). Extended-range VLANs
(IDs greater than 1005) are not supported by
VTP.
VTP Overview
VTP allows a network manager to make
changes on a switch that is configured as a
VTP server.
The VTP server distributes and synchronizes
VLAN information to all VTP-enabled switches in
the entire network.
VTP stores VLAN configurations in the VLAN
database called vlan.dat.
For example: In the figure, a trunk link is
added between S1, a VTP server, and S2, a
VTP client.
After a trunk is established and becomes
active, VTP advertisements are exchanged
 Benefits of VTP
VTP maintains VLAN
configuration consistency by
managing the following vlan
information in a switch
network:
Addition
Deletion
Renaming
VTP offers a number of
benefits for network managers,
as shown in the figure.
 VTP Components
VTP Domain - Consists of one or more
interconnected (by trunk links) switches.
All switches in a domain share VLAN configuration
details using VTP advertisements.
Router or Layer 3 switch defines the boundary of
domain.
VTP Modes - 3 different VTP modes
VTP Server - VTP servers advertise the VTP VLAN
information to other switches in the same VTP
domain.
VTP servers store the VLAN information for the domain
in NVRAM.
The server is where VLAN 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.
A VTP client only stores the VLAN information while the
switch is on.
A switch reset deletes the VLAN information. You
must then 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 Components (continue)
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 VTP pruning, a switch
floods broadcast, multicast, and
unknown unicast traffic across all
trunk links within a VTP domain.
VTP Advertisements - VTP uses
a hierarchy of advertisements
to distribute and synchronize
VLAN configurations across
the network.
VTP
 Default VTP Configuration
The Cisco command show VTP status displays the VTP status.
The default VTP settings are.
VTP Version = 1
VTP Domain Name = null
VTP Mode = Server
Configuration Revision = 0
VLANs = 1
The following briefly describes the show VTP status parameters:
VTP Version - Displays the VTP version the switch is
running.
There are 3 versions but by default, the switch
implements version 1.
Only one VTP version is allowed in a VTP domain.
Configuration Revision - Current configuration revision
number. (if this is 0, and this switch is part of the domain
then other switchs advertisements will be considered more
recent)
Maximum VLANs Supported Locally Is the 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.
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.
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.
 VTP Domains
VTP allows you to separate your
network into smaller management
domains to help reduce VLAN
management.
A VTP domain consists of one switch or
several interconnected switches sharing
the same VTP domain name.
An additional benefit of configuring VTP
domains is that it limits the size to which
configuration changes are propagated in
the network if an error occurs.
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.
 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.
Domain name propagation uses three VTP
components: servers, clients, and advertisements.
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.
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.
Cisco recommends that access to the domain
name configuration functions be protected by a
password.
 Adding a switch to the VTP
Domain
If a switch fails, and you need to
replace it with one that has
previously been used, make sure you
CHANGE THE VTP DOMAIN NAME on
the switch before adding it to the
network, otherwise, it could send
incorrect VLAN information onto the
network.
 VTP Revision Number
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 configuration revision number is a 32-bit
number.
The default revision 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 figure shows a network manager adding
three VLANs to switch S1.
The highlighted area shows that the revision
number on switch S1 is 3,
The number of VLANs is 8,
because 3 VLANs have been added to the 5
default VLANs.
 VTP Modes Overview
Server Mode MUST BE TRUNKED to do thisnot in access mode!
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 track of updates through a configuration revision number.
Other switches in the same VTP domain compare their configuration
revision 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.
The VLAN configuration information that a VTP client switch receives from
a VTP server switch is stored in a VLAN database, not in NVRAM.
When a VTP client is shut down and restarted, it sends a request
advertisement to a VTP server for updated VLAN information.
Transparent Mode
Switches configured in transparent mode forward VTP advertisements that
they receive on trunk ports to other switches.
VTP transparent mode switches do not advertise their VLAN and do not
synchronize their VLAN configuration with other switches, however, they
do pass that information on to other switches.
If a VTP transparent mode switch is restarted, it does not revert to a
default VTP server mode, but remains in VTP transparent mode.
 VTP pruning

(Cutting)
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. ONLY
SERVERS can do this!
In the figure, you would enable VTP
pruning on switch S1.
Switch S3 has VLAN 20 configured,
Switch S2 has VLAN 10 and VLAN 20
configured.
 VTP Pruning Enabled
The figure shows a network The highlighted area shows that
topology that has switches S1, S2, the trunk on port F0/1 allows
VLAN 10 traffic.
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.
VTP pruning only prunes the way
out port.
The highlighted area shows that the
trunk on port F0/1 does not allow
VLAN 10 traffic. VLAN 10 is not listed.
 VTP Configuration Guidelines
VTP Server Switches
Confirm that all of the switches you are configuring have been set to
default settings.
Configure at least two VTP server switches in your network.
In case the primary VTP server becomes disabled, if all the switches
are in VTP client mode, you cannot create new VLANs on the network.
Configure a VTP domain on the VTP server.
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.
Switches without password or with the wrong password reject VTP
advertisements.
Ensure that all switches are configured to use the same VTP 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.
Create the VLAN after you have enabled VTP on the VTP server.
VTP information is only exchanged on trunk ports.
 VTP Configuration Guidelines
VTP Client Switches
As on the VTP server switch, confirm that
the default settings are present.
Configure VTP client mode.
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, it
takes a few moments for the various
advertisements to make their way back
and forth to the VTP server.
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
Initially none of the devices are connected.
The topology highlights switch S1. You will
configure this switch to be a VTP server.
The output of the show vtp status command
confirms that the switch is by default a VTP
server.
the revision number is still set to 0
the switch does not belong to VTP domain.

Configure the VTP Server

If the switch was not already configured as a
VTP server, you could configure it using the
vtp mode server command.
The domain name is configured using the vtp
domain domain-name command.
switch S1 has been configured with the
domain name cisco1.
For security reasons, a password could be
configured using the vtp password password
command.
The default version for Catalyst 2960 is version
1.
Assume that three VLANs have been configured
and have been assigned VLANs names.
 Configuring VTP: Step 2
Configure the VTP client3.

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.
Configure the VTP Client
Before configuring a switch as a VTP
client, verify its current VTP status.
Show vtp status
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.
 Configuring VTP: Step 3 Confirm and Connect
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.
Confirm VTP Operation
There are 2 commands for confirming that
VTP domain and VLAN configurations have
been transferred.
Use 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 show vtp counters command to confirm
that the advertisements took place.
Configure Access Ports
The task now is to configure the port F0/11
on switch S2 to be in VLAN 20. Use the
switchport access vlan [number] interface
command
 Troubleshooting VTP
Connections
In this topic, you will learn about
common VTP configuration problems.
This information, combined with your
VTP configuration skills, will help you
troubleshooting VTP configuration
problems.
 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.
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.
 Troubleshooting VTP: 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 . It must be set
manualy
 Troubleshooting VTP: Incorrect VTP Domain Name
The VTP domain name is a key parameter
that is set on a switch.
An incorrectly 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.
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.
 Troubleshooting VTP: 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.
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.
 Summary
VTP is a Cisco proprietary protocol used to
exchange VLAN information across trunk links.
A switch can be in one of 3 VTP operating
modes
Client
Cannot create, modify or delete VLAN
Server
Can create, modify & delete VLAN
Transparent
Can create, modify, & delete LOCAL VLAN
Forwards VTP advertisements.
 Summary
VTP pruning
Limits unnecessary distribution of VLAN
information.
Verify VTP configuration
Show VTP status
Show interfaces trunk