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gwhuang5398
Explorer

Does VTP domain matter if "switchport mode trunk"?

If I have two switches with trunks in between, assuming I configure the trunk ports on both switches as "switchport mode trunk". would the trunk come up if the VTP domain names are dfferent on two swtiches?

Thanks

Gary

12 REPLIES 12

Hi,

Yes The trunk come up.

Best regards.

Massimiliano.

hi

I think "switchport mode trunk" alone configured will still send dtp messages.hence u need to configure "switchport nonegotiate" in this case..

arun

If I don't configure any "vtp domain ..." statement, would that solve the problem or not work at all?

Gar

hi,

If you do not configure any domain name on both switches then the doamin name used will be blank.In this case the trunk should come up.

HTH,

regards,

shri :)

Yes as above said the for DTP to make the trunk up the VTP domain should be same ,or one or both end should be NULL(by default)..

arun

Hi,

Trunk will come up and works fine even if the vtp domain names are different and in diff modes. I have tested....

I too think so, what does VTP domain/ VTP has to do with bringing truk up/down? If it has something to do kindly share it with all of us.

--gaurav

hi,

AFAIK while using DTP negotiations the VTP domain name is checked and if unmatched the trunk will not came up.If you configure the trunk as nonegotiate then the domain name is not considered.

HTH,

regards,

shri :)

Hi ,

Just for ur reference,Pls read out DTP session..

http://cisco.iphelp.ru/doc/3/Cisco.Press,.CCNP.Self-Study.CCNP.Practical.Studies.Switching.(2003).(INTERNAL).BBL.LotB/1587200600/ch03lev1sec3.html

arun

Thanks all for the help. I think if DTP is not involved in the trunk establishing process, then VTP domain name does not matter. I somehow have the impression that if the port mode is set to "trunk", DTP will not have negotiation between the two interfaces, so the trunk would come up regardless. Please let me know if I misunderstood it.

Gary

As i understand the DTP messages are still send evenif u configure mode to "trunk" only..

The dtp messesages are stopped only with "nonegogiate" option

arun

If you run switchport mode trunk with the nonegotiate option then the vtp domain names do not matter as dtp frames will not be sent . If you configure them to dynamically create the trunks with the option switchport mode dynamic desirable or auto then the vtp domain names do matter and the trunk will not come active unless they match. That being said if you force them on all the switch has to see is a physical link and it will say it is trunking when it might not be if configured incorrectly so that is the danger of forcing them on . When you use dynamic trunk protocols this problem is eliminated.