The document discusses VLAN Trunking Protocol (VTP), which allows VLAN configurations to be automatically propagated across multiple switches to reduce configuration errors and maintenance. VTP operates by defining a VTP domain where one switch acts as a server to send VLAN information to other client switches. It describes how VTP advertisements are sent and processed to update switches when VLANs are added or modified on the server. The roles of server, client, and transparent modes are also outlined.

1. VLAN Trunking
protocol
CCNA Exploration Semester 3
Chapter 4
30 Sep 2012 S Ward Abingdon and Witney College 1

2. 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

3. Semester 3
LAN Design
Basic Switch Wireless
Concepts
VLANs STP
VTP Inter-VLAN
routing
3
30 Sep 2012 S Ward Abingdon and
Witney College

4. 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
30 Sep 2012 S Ward Abingdon and
Witney College

5. 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
30 Sep 2012 S Ward Abingdon and
Witney College

6. 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
30 Sep 2012 S Ward Abingdon and
Witney College

7. 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
30 Sep 2012 S Ward Abingdon and
Witney College

8. 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
30 Sep 2012 S Ward Abingdon and
Witney College

9. 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
30 Sep 2012 S Ward Abingdon and
Witney College

10. 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
30 Sep 2012 S Ward Abingdon and
Witney College

11. 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
30 Sep 2012 S Ward Abingdon and
Witney College

12. 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
30 Sep 2012 S Ward Abingdon and
Witney College

13. 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
30 Sep 2012 S Ward Abingdon and
Witney College

14. 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
30 Sep 2012 S Ward Abingdon and
Witney College

15. 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
30 Sep 2012 S Ward Abingdon and
Witney College

16. 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
30 Sep 2012 S Ward Abingdon and
Witney College

17. 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
30 Sep 2012 S Ward Abingdon and
Witney College

18. 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
30 Sep 2012 S Ward Abingdon and
Witney College

19. 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
30 Sep 2012 S Ward Abingdon and
Witney College

20. 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
30 Sep 2012 S Ward Abingdon and
Witney College

21. 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
30 Sep 2012 S Ward Abingdon and
Witney College

22. 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
30 Sep 2012 S Ward Abingdon and
Witney College

23. 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
30 Sep 2012 S Ward Abingdon and
Witney College

24. 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
30 Sep 2012 S Ward Abingdon and
Witney College

25. 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
30 Sep 2012 S Ward Abingdon and
Witney College

26. 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
30 Sep 2012 S Ward Abingdon and
Witney College

27. Commands on server
 Create VLANs
 Check that link is a trunk.
 Check VTP operation
 SW1# show vtp status
 Assign switch ports to VLANs.
27
30 Sep 2012 S Ward Abingdon and
Witney College

28. 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
30 Sep 2012 S Ward Abingdon and
Witney College

29. 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
30 Sep 2012 S Ward Abingdon and
Witney College

30. The End
30 Sep 2012 S Ward Abingdon and Witney College 30