�ݺ�ߣ

VLAN Trunking
protocol
CCNA Exploration Semester 3
Chapter 4

30 Sep 2012 S Ward Abingdon and Witney College 1

Topics
 The role of VLAN Trunking Protocol (VTP)
 Operation of VTP

 Configure VTP on switches

2
30 Sep 2012 S Ward Abingdon and
Witney College

Semester 3
LAN Design

Basic Switch Wireless
Concepts

VLANs STP

VTP Inter-VLAN
routing
3
Witney College

Purpose of VTP
 You can create VLANs on a switch.
 What if you have the same VLANs on 10
linked switches? Or 100 linked switches?
 Do you have to create the VLANs on every
switch and allow them on each trunk?
 VTP helps.

 But you still have to assign access ports to
VLANs on each switch.
4
Witney College

VTP domain
 Group of layer 2 switches sharing VLAN data.
 Ends at router or layer 3 switch.

 Switch can be linked but not part of domain.

 Each switch can belong to only one domain.

 Domain is defined by its name.

 Proprietary to Cisco, so all switches in
domain must be Cisco switches.

5
Witney College

VTP server
 One switch acts as server.
 Create VLANs on this switch.

 Information saved in vlan.dat.

 Server sends VLAN information to client
switches over active trunk links.
 Add, delete, rename VLANs on server.

 Default mode of switch is server.

6
Witney College

VTP client
 Client receives VLAN information from
server.
 Client switches then have the same VLANs
as the server.
 Client does not save VLAN information. It is
held only in RAM and lost if switch is
powered off.

7
Witney College

VTP modes
 Server – default mode. Sends VLAN
information to other switches.
 Client – receives VLAN information and
forwards it to other switches.
 Transparent – forward VTP traffic but do not
originate or use it. They can have their own
VLANs, not shared with other switches.

8
Witney College

VTP defaults
 Version 1. (Versions 2 and 3 also exist.)
 VTP domain name is not set.

 VTP mode server

 One active VLAN, VLAN 1

 Configuration revision number 0

 Any switches added to a domain should be in
the default condition or they may send
unwanted information to other switches.
9
Witney College

Show vtp status
 VTP Version
 Maximum VLANs Supported
 Number of Existing VLANs
 VTP Operating Mode- server, client, or transparent.
 VTP Domain Name
 VTP Pruning Mode
 VTP V2 Mode (disabled by default)
 VTP Traps Generation
 MD5 Digest (checksum of VTP configuration)
 Configuration Last Modified
10
Witney College

VTP advertisements
 Consist of VTP header and VTP message
 Encapsulated inside Ethernet frame with tag
to pass over trunk link.
 Destination MAC address is multicast
address 01-00-0C-CC-CC-CC

11
Witney College

VTP message header
 Domain name
 Domain name length

 Version - VTP 1 or VTP 2, on Cisco 2960
switch.
 Configuration revision number

 Other fields, depending on type of message.

12
Witney College

Configuration revision number
 32-bit number.
 Default value is 0.

 It is incremented each time a VLAN is added
or removed.
 Reset to 0 is domain name changes.

 Switch uses it to see if information is more
recent that what it already holds.

13
Witney College

Summary advertisement
 Sent immediately after a change is made,
with updated revision number.
 Sent every 5 minutes by servers and clients
to check on current VTP configuration
revision number.
 Contains the VTP domain name, the current
revision number, and other VTP configuration
details.

14
Witney College

VTP Summary advertisement
 A switch receives a summary advertisement.
 Compares domain name to its own domain name.
 If name is different, the switch ignores the packet.
 If the name is the same, the switch compares the
revision number to its own revision number.
 Number higher or equal, ignored the packet.
 Number lower, sends an advertisement request.

15
Witney College

Request Advertisement
Sent by client to server 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

16
Witney College

Subset advertisement
 Contains VLAN information. Several may be
needed if there is a lot of information.
 Sent by server in response to a request or
after:
 Creating or deleting a VLAN
 Suspending or activating a VLAN
 Changing the name of a VLAN
 Changing the MTU of a VLAN

17
Witney College

Subset advertisement

Version Code Seq-number Domain name length
Management domain name (padded to 32 bytes)
Configuration revision number
VLAN info field 1
VLAN info field 2
Etc.

18
Witney College

Subset advertisement VLAN info
VLAN-Info
Info length Status VLAN-Type VLAN-name
Len
ISL VLAN ID MTU size

802.10 index

VLAN name (padded to multiple of 4 bytes)

19
Witney College

Pros and cons
 Small network – don’t bother with VTP.
 Big network – good for consistency and
easier to make changes.
 Server switches need lots of flash memory,
clients do not.
 Redundancy – don’t have everything on one
server switch.
 Problems from large domains.
 Extreme care when adding a switch.

20
Witney College

Why transparent?
 Put a switch in transparent mode if it has
local VLANs that are not on other switches.
 The other switches do not need to know
about them.

21
Witney College

VTP pruning
 Disabled by default
 Enable it on one server in domain.

 Stops VLAN traffic from being sent on links
that do not lead to devices on that VLAN.
 Cuts down on traffic on trunk links.

22
Witney College

Domain names and passwords
 Configure a domain name on the first server
switch. The other switches will learn it.
 If you configure it on other switches, check
that it is exactly the same. It is case sensitive.
 If you use a password then it must be exactly
the same on all switches.

23
Witney College

Versions
 VTP version 1 is used by default on Catalyst
switches, but they can use version 2.
 If you configure version 2 on one switch then
the other switches should learn the new
version and change to it.
 If a switch is not capable of running version 2
then it will not exchange advertisements.

24
Witney College

Configure VTP
 Configure VTP with a domain name before
creating VLANs on the server.
 Existing VLANs are removed when you start
to configure VTP.
 Check that links are trunk links.

 Configure client switches to client mode.

25
Witney College

Commands on server
 SW1(config)#vtp domain cisco1
 SW1(config)#vtp password cisco

 (Password is optional)

 Server mode is default, but if it was changed:

 SW1(config)#vtp mode server

 Version 1 is default, but command is:

 SW1(config)#vtp version 1

26
Witney College

Commands on server
 Create VLANs
 Check that link is a trunk.

 Check VTP operation

 SW1# show vtp status

 Assign switch ports to VLANs.

27
Witney College

Client configuration
 SW2(config)#vtp mode client

 Check that link is a trunk.
 Check VTP operation

 SW2# show vtp status

 Assign switch ports to VLANs.

28
Witney College

Things to check
 VTP Version. It needs to be the same on all
switches in the domain.
 Domain name. Is it exactly the same on all
switches?
 VTP Password if any. Is it exactly the same on all
switches?
 Check that there is at least one server. Better to
have at least two.
 If you recently added a new switch, had its revision
number been set to 0?
29
Witney College

The End

30 Sep 2012 S Ward Abingdon and Witney College 30

�ݺ�ߣ

Chapter 4 vtp

More Related Content

Chapter 4 vtp