Apr
25

Here ye, here ye, VTP experts. (We are not referring to the Vandenberg Test Program, although they are very likely experts in their field as well.  :))

Can you predict the results of a 3 switch VTP client/server scenario?

SW1-3, are connected, as shown in the diagram.

VTP question for Blog

Here is the initial output of show VTP status, and show VLAN brief on each. Note that SW1 and SW3 are servers, while SW2 is a client.   We will be adding a failure to the network in just a moment.

SW1#show vtp status
VTP Version : 2
Configuration Revision : 3
Maximum VLANs supported locally : 1005
Number of existing VLANs : 8
VTP Operating Mode : Server
VTP Domain Name : INE
VTP Pruning Mode : Disabled
VTP V2 Mode : Disabled
VTP Traps Generation : Disabled
MD5 digest : 0x2C 0x04 0x21 0x2B 0x10 0xFE 0x03 0x50
Configuration last modified by 0.0.0.0 at 3-1-93 00:05:40
Local updater ID is 0.0.0.0 (no valid interface found)
SW1#show vlan brief

VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Fa0/1, Fa0/2, Fa0/3, Fa0/4
Fa0/5, Fa0/6, Fa0/7, Fa0/8
Fa0/9, Fa0/10, Fa0/11, Fa0/12
Fa0/13, Fa0/14, Fa0/15, Fa0/16
Fa0/17, Fa0/18, Fa0/19, Fa0/20
Fa0/21, Fa0/22, Fa0/23, Gig0/1
Gig0/2
2 VLAN0002 active
3 VLAN0003 active
4 VLAN0004 active
1002 fddi-default active
1003 token-ring-default active
1004 fddinet-default active
1005 trnet-default active
SW1#

SW2#show vtp status
VTP Version : 2
Configuration Revision : 3
Maximum VLANs supported locally : 1005
Number of existing VLANs : 8
VTP Operating Mode : Client
VTP Domain Name : INE
VTP Pruning Mode : Disabled
VTP V2 Mode : Disabled
VTP Traps Generation : Disabled
MD5 digest : 0x2C 0x04 0x21 0x2B 0x10 0xFE 0x03 0x50
Configuration last modified by 0.0.0.0 at 3-1-93 00:05:40
SW2#show vlan brief

VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Fa0/2, Fa0/3, Fa0/4, Fa0/5
Fa0/6, Fa0/7, Fa0/8, Fa0/9
Fa0/10, Fa0/11, Fa0/12, Fa0/13
Fa0/14, Fa0/15, Fa0/16, Fa0/17
Fa0/18, Fa0/19, Fa0/20, Fa0/21
Fa0/22, Fa0/23, Gig0/1, Gig0/2
2 VLAN0002 active
3 VLAN0003 active
4 VLAN0004 active
1002 fddi-default active
1003 token-ring-default active
1004 fddinet-default active
1005 trnet-default active
SW2#

SW3#show vtp status
VTP Version : 2
Configuration Revision : 3
Maximum VLANs supported locally : 1005
Number of existing VLANs : 8
VTP Operating Mode : Server
VTP Domain Name : INE
VTP Pruning Mode : Disabled
VTP V2 Mode : Disabled
VTP Traps Generation : Disabled
MD5 digest : 0x2C 0x04 0x21 0x2B 0x10 0xFE 0x03 0x50
Configuration last modified by 0.0.0.0 at 3-1-93 00:05:40
Local updater ID is 0.0.0.0 (no valid interface found)
SW3#show vlan brief

VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Fa0/2, Fa0/3, Fa0/4, Fa0/5
Fa0/6, Fa0/7, Fa0/8, Fa0/9
Fa0/10, Fa0/11, Fa0/12, Fa0/13
Fa0/14, Fa0/15, Fa0/16, Fa0/17
Fa0/18, Fa0/19, Fa0/20, Fa0/21
Fa0/22, Fa0/23, Fa0/24, Gig0/1
Gig0/2
2 VLAN0002 active
3 VLAN0003 active
4 VLAN0004 active
1002 fddi-default active
1003 token-ring-default active
1004 fddinet-default active
1005 trnet-default active
SW3#

So here is the scenario for the question. The Fa0/24 connection is suddenly broken between SW1 and SW2, and while that is down, a new VLAN (we will use 999)  is created on SW3 like this:

<strong>SW3(config)#vlan 999</strong>

And then, a few minutes later, SW3 is completely powered off, shipped to another city, and removed completely from this network forever.

If we then restore the Fa0/24 connection between SW1 (the server) and SW2 (the client) what will happen to the VTP/VLAN information on the two switches? Will there be an update on either switch, will SW1 wait for a Server advertisement or will something else happen all together?

Take a moment, and let us know what you think.

Best wishes.

PS We’ll post the results as a after you have had some time to consider the results.

A few hours have passed, and we have had over 50 comments , ideas and theories.

I appreciate you taking the time to work through this.  May your hard work pay off with a successful lab.

And the correct answer is:

SW1, will see that its configuration revision number is lower than SW2, and even though SW2 is a "client" SW1 will use the updated information in the VTP advertisement from SW2 to update to its VLAN database, and get in "sync" with the rest of the VTP domain, including knowing about VLAN 999.   The configuration revision number would also move to 4.

Here is SW1, after the connection to SW2 is restored:

SW1#show vtp status
VTP Version : 2
Configuration Revision : 4
Maximum VLANs supported locally : 1005
Number of existing VLANs : 9
VTP Operating Mode : Server
VTP Domain Name : INE
VTP Pruning Mode : Disabled
VTP V2 Mode : Disabled
VTP Traps Generation : Disabled
MD5 digest : 0x45 0x1D 0x6E 0xF0 0xB7 0xC2 0x84 0xFA
Configuration last modified by 0.0.0.0 at 3-1-93 00:11:43
Local updater ID is 0.0.0.0 (no valid interface found)
SW1#show vlan brief

VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Fa0/1, Fa0/2, Fa0/3, Fa0/4
Fa0/5, Fa0/6, Fa0/7, Fa0/8
Fa0/9, Fa0/10, Fa0/11, Fa0/12
Fa0/13, Fa0/14, Fa0/15, Fa0/16
Fa0/17, Fa0/18, Fa0/19, Fa0/20
Fa0/21, Fa0/22, Fa0/23, Gig0/1
Gig0/2
2 VLAN0002 active
3 VLAN0003 active
4 VLAN0004 active
999 VLAN0999 active
1002 fddi-default active
1003 token-ring-default active
1004 fddinet-default active
1005 trnet-default active
SW1#

Here is SW2:

SW2#show vtp status
VTP Version : 2
Configuration Revision : 4
Maximum VLANs supported locally : 1005
Number of existing VLANs : 9
VTP Operating Mode : Client
VTP Domain Name : INE
VTP Pruning Mode : Disabled
VTP V2 Mode : Disabled
VTP Traps Generation : Disabled
MD5 digest : 0x45 0x1D 0x6E 0xF0 0xB7 0xC2 0x84 0xFA
Configuration last modified by 0.0.0.0 at 3-1-93 00:11:43
SW2#show vlan brief

VLAN Name Status Ports
---- -------------------------------- --------- -------------------------------
1 default active Fa0/1, Fa0/2, Fa0/3, Fa0/4
Fa0/5, Fa0/6, Fa0/7, Fa0/8
Fa0/9, Fa0/10, Fa0/11, Fa0/12
Fa0/13, Fa0/14, Fa0/15, Fa0/16
Fa0/17, Fa0/18, Fa0/19, Fa0/20
Fa0/21, Fa0/22, Fa0/23, Gig0/1
Gig0/2
2 VLAN0002 active
3 VLAN0003 active
4 VLAN0004 active
999 VLAN0999 active
1002 fddi-default active
1003 token-ring-default active
1004 fddinet-default active
1005 trnet-default active
SW2#

Thanks again everyone, and happy studies!

INE Instructor
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