switch in vtp client mode

Answered Question
Nov 16th, 2008
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hi every body!

Does switch in vtp client mode stores config revision number in vlan.dat or nvram?

i find some cisco documents which say client switch store config revision number in vlan.dat on flash while my cisco press book says client switch stores config revision number in nvram

which one is correct?

thanks a lot and have a nice day!

Correct Answer by Edison Ortiz about 8 years 7 months ago

During my test, I also found the VTP Client keeps the Vlans that were obtained from the VTP server.


All that information is tied together in the vlan.dat file so indeed - a VTP Client can bring a network down in some situations such as 'higher revision number'.


Best Practice is to delete the vlan.dat file on any new switch being inserted into a production network.


Keep hitting those books, you are bringing up very useful topics into these forums :)


Here is some output from an isolated switch:


S4#sh vtp status

VTP Version : 2

Configuration Revision : 14

Maximum VLANs supported locally : 1005

Number of existing VLANs : 14

VTP Operating Mode : Client

VTP Domain Name : NET34


Trying to create a Vlan:


S4(config)#vlan 33

VTP VLAN configuration not allowed when device is in CLIENT mode.


No other switch connected:


S4#sh int trunk


S4#


Vlans obtained from a VTP Server before rebooting:


S4#sh vlan | e unsup


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, Fa0/24

Gi0/1, Gi0/2

4 VLAN0004 active

10 VLAN_10 active

40 VLAN0040 active

45 VLAN0045 active

49 VLAN0049 active

50 VLAN0050 active

59 VLAN0059 active

100 VLAN0100 active

363 VLAN0363 active



BTW, I deleted NVRAM: "startup-config" and "private-config" files and it deleted my original configuration but the Vlan information was kept intact since they are kept in Vlan.dat as I previously stated.


__


Edison.

Correct Answer by Edison Ortiz about 8 years 7 months ago

Sarah,


I really praise you for your quest in obtaining the right information.


It inspired me to test this behavior in the lab and my results concluded the VTP information is held in the vlan.dat file.


I had a switch running in VTP Client mode and after deleting the vlan.dat file, the switch reverted back to VTP server after reboot.


In conclusion, the switch VTP status information is held in Vlan.dat while the Vlan information is provided by the VTP server.


Thanks for making me re-learn one of those obscures behavior within VTP.


Regards,


__


Edison.

Correct Answer by Edison Ortiz about 8 years 7 months ago

I mean this


store vlan information and vtp information in nvram


All the information is obtained from the current VTP Server(s). If you turn off a VTP Client switch and turn it back on w/o VTP Server(s) being available, the switch won't have any Vlan information.


__


Edison.

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Edison Ortiz Sun, 11/16/2008 - 19:09
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The Cisco Press Book is correct.


http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_44_se/configuration/guide/swvtp.html#wp1035285


If you configure the switch for VTP client mode, the switch does not create the VLAN database file (vlan.dat). If the switch is then powered off, it resets the VTP configuration to the default. To keep the VTP configuration with VTP client mode after the switch restarts, you must first configure the VTP domain name before the VTP mode.


HTH,


__


Edison.

sarahr202 Mon, 11/17/2008 - 05:10
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thanks for your reply. I think switch in client mode store vlan and vtp information in vlan.dat. Is it correct?

thanks!

Edison Ortiz Mon, 11/17/2008 - 05:13
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No, NVRAM.


Vlan.dat is used on VTP Servers.


__


Edison.

sarahr202 Mon, 11/17/2008 - 05:24
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thanks for your reply! you mean switch in client mode

1) store vlan information and vtp information in nvram


or

does not store at all vlan information just vtp information in nvram.

thanks a lot!

Correct Answer
Edison Ortiz Mon, 11/17/2008 - 05:27
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I mean this


store vlan information and vtp information in nvram


All the information is obtained from the current VTP Server(s). If you turn off a VTP Client switch and turn it back on w/o VTP Server(s) being available, the switch won't have any Vlan information.


__


Edison.

sarahr202 Mon, 11/17/2008 - 17:12
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sorry to bother you.

nvram does not lose its contents upon reboot. So if the client switch store vlan and vtp information in nvram, and we turn off the switch in server mode and reboots the client switch, it should have vlan information because vlan information was stored in nvram.

thanks a lot!

Edison Ortiz Mon, 11/17/2008 - 17:59
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Stand corrected and I must word my answer better, the information technically isn't saved anywhere in the VTP Client as the device request this information from the VTP Server as needed.


Sarah, you deserve some rating :)


__


Edison.

sarahr202 Mon, 11/17/2008 - 18:41
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thanks a lot Edison for your kind remarks!

So switch in client mode stores only vtp domain and config revision number in nvram?

Does it require the use of " copy running-config startup-config" ?

thanks a lot!

Edison Ortiz Mon, 11/17/2008 - 19:02
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According to this link

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_35_se/configuration/guide/swvtp.html#wp1205076


It isn't saved anywhere. If the information is saved, it can be reused later but as you know, a reboot of the switch in an isolated area will result a switch w/o vlan information.


__


Edison.

sarahr202 Mon, 11/17/2008 - 19:30
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Sorry Edison for this long post!

The link you forwarded says no vlan information is stored in nvram (if the switch in client mode).

It does not say anything about vtp information if it is stored or not.

However, before i posted my question , i read few cisco documents which say switch in client mode store vtp domain name and config revision number in nvram. Those documents do not say anything how this vtp information is saved i.e Do we need to use Copy running-config startup-config or switch in client mode automatically stores vtp informartion in nvram.

thanks a lot!

darren-carr Mon, 11/17/2008 - 21:04
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sarah202,


If in client mode the vlan info is not stored in NVRAM. If the switch is rebooted it will lose the VLAN info and will relearn it if it can access a VTP server in the same VTP domain when it loads. If it cannot contact a VTP server it will not learn the VTP domain information.


If configured VTP transparent (after being configured as a client initially) the file is saved into NVRAM so if rebooted the VLAN data will remain the same. Only issue with this is that if the VLAN info is changed on the server it will not auto update. You need to change the mode back to client for it to update then back to transparent to store the new config in NVRAM.


If configured as a server you can edit the vlan info, etc and it can push this out to your clients.


In our environment we have two VTP servers, the rest of the switches are saved as transparent with pruning enabled.


Benefit of this is that we only maintain one server for updating the VLAN info, we do have to change each switch to client thought to propogate the change to the network but this gives us control over who can do what and stops the network from being destroyed!!! :)


Hope this helps


Darren

Correct Answer
Edison Ortiz Tue, 11/18/2008 - 05:42
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Sarah,


I really praise you for your quest in obtaining the right information.


It inspired me to test this behavior in the lab and my results concluded the VTP information is held in the vlan.dat file.


I had a switch running in VTP Client mode and after deleting the vlan.dat file, the switch reverted back to VTP server after reboot.


In conclusion, the switch VTP status information is held in Vlan.dat while the Vlan information is provided by the VTP server.


Thanks for making me re-learn one of those obscures behavior within VTP.


Regards,


__


Edison.

sarahr202 Tue, 11/18/2008 - 06:22
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Thanks a lot for your kind remarks Edison!

I have no resources to afford school or buy equipments. My teachers are people like you on this net pro and my book.

Anyway now I know the location where switch in client mode store vtp information. It is very discouraging that cisco own documents are full of contradictions .

According to following link:

{under the "common issues" link in the flash)

http://www.cisco.com/warp/public/473/vtp_flash/

switch in client mode does not store any vlan information ,rather it depends upon vtp server to receive vlans informations.

In the above flash, a swicth in client mode , with higher config revision number, is inserted in a domain to demonstrate how it will bring the network down.

The only problem is ,client switch inserted in the domain , still had vlans 200-300, with high config revision number.

My point as client switch does not store vlan informations, how come the inserted switch in client mode still had vlans 200-300, It should have only default vlan i.e vlan 1 nothing else.

Any comment will be greatly appreciated.

Thanks a lot and have a nice day!


Correct Answer
Edison Ortiz Tue, 11/18/2008 - 06:30
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During my test, I also found the VTP Client keeps the Vlans that were obtained from the VTP server.


All that information is tied together in the vlan.dat file so indeed - a VTP Client can bring a network down in some situations such as 'higher revision number'.


Best Practice is to delete the vlan.dat file on any new switch being inserted into a production network.


Keep hitting those books, you are bringing up very useful topics into these forums :)


Here is some output from an isolated switch:


S4#sh vtp status

VTP Version : 2

Configuration Revision : 14

Maximum VLANs supported locally : 1005

Number of existing VLANs : 14

VTP Operating Mode : Client

VTP Domain Name : NET34


Trying to create a Vlan:


S4(config)#vlan 33

VTP VLAN configuration not allowed when device is in CLIENT mode.


No other switch connected:


S4#sh int trunk


S4#


Vlans obtained from a VTP Server before rebooting:


S4#sh vlan | e unsup


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, Fa0/24

Gi0/1, Gi0/2

4 VLAN0004 active

10 VLAN_10 active

40 VLAN0040 active

45 VLAN0045 active

49 VLAN0049 active

50 VLAN0050 active

59 VLAN0059 active

100 VLAN0100 active

363 VLAN0363 active



BTW, I deleted NVRAM: "startup-config" and "private-config" files and it deleted my original configuration but the Vlan information was kept intact since they are kept in Vlan.dat as I previously stated.


__


Edison.

sarahr202 Tue, 11/18/2008 - 07:15
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Thanks a lot Edison!Thanks to you ,the whole mystery is solved .


Jon Marshall Thu, 12/04/2008 - 14:02
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It depends on the switch as to where the vlan.dat file lives but on most switches


delete flash:vlan.dat


do a "sh flash" first to check the vlan.dat file is in flash.


Jon

darren-carr Thu, 12/04/2008 - 14:06
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Jon,


Correct me if im wrong, but doesn't delete just mark the file for deletion? to actually remove the file permanently you have to use the 'erase' option?


D

Jon Marshall Thu, 12/04/2008 - 14:14
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Darren


It does vary from switch to switch ie. the 4500/6500 switches use the erase command but with the fixed switches ie. 29xx/35xx/37xx the delete has usually worked for me. I'll boot up a 3550 tomorrow and check :-)


Jon

darren-carr Thu, 12/04/2008 - 14:16
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Jon,


I agree :) does vary maybe its just what I have been using of late :)

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