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CCNA3 VTP (VLAN Trunking Protocol) (Commands (Check the current VTP mode:…
CCNA3 VTP (VLAN Trunking Protocol)
What is it?
A protocol used to synchronize information related to VLAN database. We can create or modify a VLAN on a switch and propagate that change to other switches
Advantages of use
Save time of administration
It has the word
trunking
in its name because messages are sent over trunk connections
VTP modes
Each switch can use one of three different VTP modes:
VTP client mode
Cannot create, change or delete VLANs by its own
Can forward its version of vlan configuration
Can forward received VTP messages to another trunk links
Can change its VLAN configuration in response of VTP messages
Global VLAN configurations are stored in
RAM
only (erased on restart)
VTP server mode
Can create and delete VLANs and propagate those changes to other switches
This is the
default mode
for Cisco switches.
Global VLAN configurations are stored in
NVAM
(preserved on restart)
VTP transparent mode
This mode doesn’t share its VLAN database
Don't participate in VTP except to forward received VTP advertisements.
This mode doesn’t change its VLAN configuration in response of VTP advertisements
Configuration Revision Number (CRN)
Every time we make a change to the VLAN database, a number is increased by one (CRN of
32-bit
)
When a switch receives an advertisement it compares the CRN of that advertisement with the CRN of its local database, if the CRN od the advertisement is higher, the switch update its local database with the configuration received
CAUTION
: if a new switch is introduced to the network and it has a CRN higher than the current in the network, the whole switch will update the configuration.
REMEMBER:
in VTP client mode and server mode the vlan configuration is sent.
VTP Versions
V2
Forwards the VTP messages without checking the version number or domain in transparent mode
Supports Token Ring
CAUTION
: in this version, if the domain name is not set statically, other switches will see VTP advertises and automatically update its domain name
V1
Supports pruning of unused VLANs(1-1001)
Default mode
on all switches
V3
Supports extended VLAN numbers (1-4095)
Protection from unintended database overrides during insertion of new switches
Support MST (a version of STP)
VTP Prunning
Is the ability of VTP to prune off unneeded VLANs from VTP advertisements
Commands
Check the current VTP mode: SW#
show vtp status
Set a specific mode: SW(config)#
vtp mode (client | server | transparent)
Set VTP domain name: SW(config)#
vtp domain
HERE-GOES-THE-NAME
Set password: SW(config)#
vtp password
HERE-GOES-THE-PASS
use SW#
show vtp password
to see the password
Set the CRN to 0: SW(config)#
vtp mode transparent
Or change the VTP domain name, and then change the name back to the original name.
VTP Advertisements
Summary advertisements
- These inform adjacent switches of VTP
domain name
and
configuration revision number.
By default, Cisco switches issue summary advertisements every
five minutes
.
Advertisement request
- These are in response to a summary advertisement message when the summary advertisement contains a higher configuration revision number than the current value.
Subset advertisements
- These contain VLAN information including any changes.