VTP

Answered Question
Oct 4th, 2008

How can a VTP domain name be learned?

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Correct Answer by glen.grant about 8 years 1 month ago

I believe switch can learn the vtp domain if the vtp domain name was at factory defaults, out of a vtp doc.

By default, the switch is in VTP server mode and is in the no-management domain state until the switch receives an advertisement for a domain over a trunk link or you configure a management domain. You cannot create or modify VLANs on a VTP server until the management domain name is specified or learned.

If the switch receives a VTP advertisement over a trunk link, it inherits the management domain name and the VTP configuration revision number. The switch remains in the first management domain learned unless changed by the user.

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Mark Yeates Sat, 10/04/2008 - 14:50

James,

A VTP domain name cannot be learned. You can specify the domain name by issuing the "vtp domain (name)" command

switch(config)#vtp domain test

HTH,

Mark

Correct Answer
glen.grant Sat, 10/04/2008 - 15:08

I believe switch can learn the vtp domain if the vtp domain name was at factory defaults, out of a vtp doc.

By default, the switch is in VTP server mode and is in the no-management domain state until the switch receives an advertisement for a domain over a trunk link or you configure a management domain. You cannot create or modify VLANs on a VTP server until the management domain name is specified or learned.

If the switch receives a VTP advertisement over a trunk link, it inherits the management domain name and the VTP configuration revision number. The switch remains in the first management domain learned unless changed by the user.

Mark Yeates Sat, 10/04/2008 - 15:50

Interesting point Glen. Isn't the default domain name a null value? Does that count as a VTP domain name? My understanding is:

When the switch receives a summary advertisement packet, it compares the VTP domain name to its own VTP domain name. If the name is different, the switch simply ignores the packet. If the name is the same, the switch then compares the configuration revision to its own revision. If its own configuration revision is higher or equal, the packet is ignored. If it is lower, an advertisement request is sent.

Mark

joshua.wilson Sat, 10/04/2008 - 16:45

shouldn't the second switch be set to client...then it will learn the vtp domain from the vtp server.

Jon Marshall Sun, 10/05/2008 - 01:12

Joshua

Yes you are correct as far as i know. Once a VTP server switch is configured with a VTP domain name then any client switches connected to the network with a trunk that do not have a VTP domain name set will learn the VTP name from the VTP server.

Jon

jwchristian87 Mon, 10/06/2008 - 13:09

UPDATE:

Everyone: just an FYI, i had both switches in server mode.

Jon: sorry, i just saw that you said in the flash file... i will go back and look at it later

glen: thanks for the info. also i read in your post and the link that jon posted"You cannot create or modify VLANs on a VTP server until the management domain name is specified or learned." do you know more about this? i am on a switch right now and i dont have a vtp domain set and i type in "Switch(config)#vlan 20" and it creates the vlan. i did notice that the revision # increases.....i would infer that null would be the domain. if that is true that means we could never not have a domain....?

jwchristian87 Mon, 10/06/2008 - 07:34

sorry for the late reply everyone. my email notifications are not working.

mark.yeates: I beleive you are correct. However, i keep reading that it can be learned.

Everyone else: my theory was that if i have a switch set to server mode with a domain name set and i connect a switch without a domain name set in client mode it would recieve the domain name. i tried that and it did not work. however i thought today that all of the client switch's ports were still on vlan 1...not sure if that made difference. i am going to the lab today. i will play around and see what i find out

Thanks everyone for your responses...i am just starting to get into forums. i hope to sharpen my knowledge some through this venue.

jwchristian87 Mon, 10/06/2008 - 12:57

ok i did some playing around and figured out that the switch will only learn the domain name if there is not a domain name set. even if you set one switch to server and one switch to client mode then change the domain name on the server the client will not learn it if one has already been set. you will get the domainname mismatch error.i think my issue before was i was on two 3560 switches and the default mode was dynamic auto. so i may have not set the trunk staticly. so you will also want to verify you are trunking. right now i am on a 2960 and 2950(the 2950 having a default of dynamic desirable)

Jon: i looked at the link you posted but still did not see anything about learning the domain name.

if anyone else wants to elaborate on this or knows more details please do!

thanks everyone

Jon Marshall Mon, 10/06/2008 - 13:01

James

You have to use the flash animation and have a bit of patience !! and you will see a new switch pick up it's domain name from a VTP server.

Yes if you don't have a domain name set on a VTP client switch and join it with a trunk to an existing VTP domain it will pick up the VTP domain. If the client switch already has a VTP domain name it will not change it.

Jon

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