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Bronze

vtp

hi every body!

I have some confusion about vtp.

In cisco press book by Wendell odom, I find this " VTP client switch can not save vlan configuration in nvram"

In cisco presss book "BCMSN" by David hucaby, i find this" vtp client switch will store the last known vtp information,including the configuration revision number"

question#1 What VTp information includes that vtp client switch maintains even upon power

cycling?

question#2 Let say we have vtp domain cisco with only two switches(just two for simplicity)sw1 and sw2.

sw1 is server and sw2 is client

sw1(server) has following configuration

ports f0/1-f0/12 are in vlan 2

ports f0/13-f0/20 are in vlan 3

When client switch (sw2) receives vtp advertisement from sw1, will it put similar ports in corresponding vlans i.e pots f0/1-f0/12 in vlan 2 and f0/13-f0/20

in vlan 3?

Thanks alot and have a nice day!

2 ACCEPTED SOLUTIONS

Accepted Solutions

Re: vtp

yes vlan database is vlan name & number.

vlan information is stored in a vlan.dat file in flash on all switches including clients.

pls use rating system to let us know that answers helped.

Re: vtp

Even though the Catalyst switch is configured as a VTP client, and not a server, it can erase the information of an existing network. Cisco explains the problem as follows:

How a Recently Inserted Switch Can Cause Network Problems

This problem occurs when you have a large switched domain, which is all in the same VTP domain, and you want to add one switch in the network. This switch was previously used in the lab, and a good VTP domain name was entered. It was configured as a VTP client, and connected to the rest of the network. Then, the trunk link was brought up to the rest of the network. In just a few seconds, the whole network is down. What could have happened? The configuration revision of the switch you inserted was higher than the configuration revision of the VTP domain. Therefore, your recently-introduced switch, with almost no configured VLANs, has erased all VLANs through the VTP domain. This happens whether the switch is a VTP client or a VTP server. A VTP client can erase VLAN information on a VTP server. You can tell that this has happened when many of the ports in your network go into inactive state, but continue to be assigned to a nonexistent VLAN.

HTH.

12 REPLIES

Re: vtp

HI, [Pls RATE if HELPS]

VTP Client will refer to the Configuration that are stored and available in VTP Server.

Whereas the VTP Client will store the VTP Information, the information includes the "Cofig revision Number"

Normally, the Config Revision Number will be issued by VTP Server and CLient's will store the Number say as VTP Information. Based on the Revision Number the Client will work.

If a VTP Client didnot receive the Latest Revision Number means, its not Updated and not working properly in the VTP Domain and it need immediate check.

Refer link below:For a Cisco Document

http://www.cisco.com/warp/public/473/21.html

VTP Configuration Guidelines:

All switches have the same the VTP domain name, unless the network design insists for different VTP domains.

Note: Trunk negotiation does not work across VTP domains.

All switches in a VTP domain must run the same VTP version.

All switches in a VTP domain has the same VTP password, if there is any.

All VTP Server switch(es) should have the same configuration revision number and it should also be the highest in the domain.

When you move a VTP mode of a switch from Transparent to Server, VLANs configured on the VTP Transparent switch should exist on the Server switch.

Hope I am informative.

Pls Rate if HELPS

Best Regards,

Guru Prasad R

Bronze

Re: vtp

hi Guru Prasad!

Thanks for your response. I already read that link before i posted this question.

It raised many questions in my mind.

I use a scenario to make my point.

sw1 (server mode) sw2(client mode)

sw1-----------sw2

trunk

sw1 and sw2 are sychronised

sw1 has following:

domain name : cisco

config revision = 2

vlan1,vlan2

sw2 has the similar config as well.

now a third switch sw3 in client mode,with pre- exiting config added to the network

domain name : cisco

config revision = 3

vlan4,vlan5.

My question is how does sw3 retains this information of vlans ? i know , isw3 can retain config revision number even if it resets.

does any one have any clue?

I also need an answer to my 2nd question which was:

IF sw1(server mode) has following config

f0/1-f0/12 in vlan2

f0/13-f0/16 in vlan 3

sw2(client mode) is connected to sw1(server).

When sw2 receive advertisements from sw1. will it put its ports likewise i.e ports f0/1-f0/12 in vlan 2 and port f0/13-f0/16 in vlan 3?

thanks alot! I really appreciate if anyone help me understand this.

Re: vtp

Let me answer your second question 1st. VTP is responsible for replicating VLAN database to the switches in domain but not the configuration. For example, if sw1 has 4 vlans in its database then onlythose 4 vlans will be replicated to rest of clients in domain. The vtp server however doesnt replicate the switch confiuration i.e. if sw1 has 2 ports each in each vlan then that port information is not circulated to clients.

To summarise, only vlan database are replicated while port configurations are not.

Now your 1st question. If you add a new switch to the domain irrespective of whether its server or client, if the config-revision number of new switch is higher than vtp server then the new switch's vlan configuration will overwrite the existing configuration.

To reset the cofig revision number number on new switch, 1st change the domain of that switch, make it transparent & again change it to clinet. This would reset the revision number.

Hope this helps clarify your doubt.

Community Member

Re: vtp

I couldnt understand that what will happen if the vtp verson of client switch is higher than that of VTP server switch

Regards

Bava

Re: vtp

If client has a higher revision number than server, client will overwrite the server's configuration with its own.

Bronze

Re: vtp

thanks alot for your response. By the way, what are the contents of vlandatabase? is there anything else besides vlan numbers ,names?

I understand that by default every switch is vtp server, thus if introduced into network will cause the problems because:

(1)That server could have higher config revision number.

(2) Being vtp server, that server retains vlan config and does not lose it even upon restting.

Now but the vtp clent switch can not hold such vlan config and will lose upon power cycling. However, it can retain config revision number in nvram. So when such client in introduced to network, how it could effect the network since it has no vlan config just only config revision number?

Simply put what client switch could have besides config revision number upon power cycling? If the client- switch can only hold config revision number, how this switch can effect the network if introduced into network?

I am sorry for this long-winded post,I really appreciate if one can clarify this.

thanks alot and have a nice day!

Re: vtp

yes vlan database is vlan name & number.

vlan information is stored in a vlan.dat file in flash on all switches including clients.

pls use rating system to let us know that answers helped.

Re: vtp

Even though the Catalyst switch is configured as a VTP client, and not a server, it can erase the information of an existing network. Cisco explains the problem as follows:

How a Recently Inserted Switch Can Cause Network Problems

This problem occurs when you have a large switched domain, which is all in the same VTP domain, and you want to add one switch in the network. This switch was previously used in the lab, and a good VTP domain name was entered. It was configured as a VTP client, and connected to the rest of the network. Then, the trunk link was brought up to the rest of the network. In just a few seconds, the whole network is down. What could have happened? The configuration revision of the switch you inserted was higher than the configuration revision of the VTP domain. Therefore, your recently-introduced switch, with almost no configured VLANs, has erased all VLANs through the VTP domain. This happens whether the switch is a VTP client or a VTP server. A VTP client can erase VLAN information on a VTP server. You can tell that this has happened when many of the ports in your network go into inactive state, but continue to be assigned to a nonexistent VLAN.

HTH.

Re: vtp

Sorry forgot the fix, erase vlan.dat file from flash and reboot - or wr erase the switch, either one should happen before you connect to the LAN.

HTH.

Bronze

Re: vtp

thanks alot Andrew!

Re: vtp

No problem - glad to help.

Bronze

Re: vtp

thanks alot!

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