trunk formation between two switches

Answered Question
Jun 13th, 2010

Hi every body.



i understand  the Dtp also report domain name in its messages. The result is  trunk will not form between two adjacent switches if they are in different vtp domain.  Let say sw1----trunk------sw2


sw1 is vtp cisco,  sw2  has its default configurations which mean vtp domain: null


Will the trunk form or it will not form ?


thanks  and have a nice weekend

Correct Answer by Giuseppe Larosa about 6 years 8 months ago

Hello Sarah,

this is tricky


a device with VTP domain null is actually ready to accept and to implement the VTP domain name it receives in a VTP message.

This is done to allow "plug and play" of new devices without configuring the vtp domain name over them.


But to receive a VTP message a working trunk is needed.


In order to have this "plug and play" feature the VTP domain name must match or one side has to show "null" as soon as the trunk is up and operational both sides will agree on VTP domain name.


Again, I haven't tested this. By the way using auto trunks is not recommended. In order to be sure of trunk operational state the use of switchport mode trunk is recommended and would solve the problem above.

This because if we rely on DTP trunk state can change over time causing also VTP db mismatches as it happened in a recent thread


note: let's wait for someone (hopefully Edison) to test it


Have a nice day you too.


Hope to help

Giuseppe

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Correct Answer
Giuseppe Larosa Sun, 06/13/2010 - 06:03

Hello Sarah,

this is tricky


a device with VTP domain null is actually ready to accept and to implement the VTP domain name it receives in a VTP message.

This is done to allow "plug and play" of new devices without configuring the vtp domain name over them.


But to receive a VTP message a working trunk is needed.


In order to have this "plug and play" feature the VTP domain name must match or one side has to show "null" as soon as the trunk is up and operational both sides will agree on VTP domain name.


Again, I haven't tested this. By the way using auto trunks is not recommended. In order to be sure of trunk operational state the use of switchport mode trunk is recommended and would solve the problem above.

This because if we rely on DTP trunk state can change over time causing also VTP db mismatches as it happened in a recent thread


note: let's wait for someone (hopefully Edison) to test it


Have a nice day you too.


Hope to help

Giuseppe

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