VTP Default Negotiation

Answered Question
Jul 22nd, 2009

Hi all. Just passed my CCCENT last week and am hitting the CCNA material - VLANS and VTP.


I understand Cisco catalyst switches default to a VLAN server but I'm having problems finding what the default VTP negotiation would be with no additional configuration. I think I understand what each mode does, just not what the default behavior is if you don't specify in the config. And, do all switchports default to an implied access port?


auto?

desireable?

trunk?

access?


TIA

Correct Answer by Edison Ortiz about 7 years 7 months ago

The default VTP status is 'Server' and 'Null domain'.


If all switches in the switched network have a 'Null domain', no VTP updates will be exchange regardless their VTP status 'Server or Client'.


If you enter a VTP Domain Name on a switch, it will automatically propagate this name on the switches with 'Null Domain' as long as the inter-switch link are trunk links.


Access switches such as 3750, 2960 and 3560 default to dynamic auto and Core switches such as 4500 and 6500 default to dynamic desirable. Note: 3550 was an oddity as it defaulted to dynamic desirable.


Auto <-> Auto does not form a trunk

Desirable <-> Auto or Desirable does form a trunk




HTH,


__


Edison.

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Correct Answer
Edison Ortiz Wed, 07/22/2009 - 06:37

The default VTP status is 'Server' and 'Null domain'.


If all switches in the switched network have a 'Null domain', no VTP updates will be exchange regardless their VTP status 'Server or Client'.


If you enter a VTP Domain Name on a switch, it will automatically propagate this name on the switches with 'Null Domain' as long as the inter-switch link are trunk links.


Access switches such as 3750, 2960 and 3560 default to dynamic auto and Core switches such as 4500 and 6500 default to dynamic desirable. Note: 3550 was an oddity as it defaulted to dynamic desirable.


Auto <-> Auto does not form a trunk

Desirable <-> Auto or Desirable does form a trunk




HTH,


__


Edison.

pipemajor Wed, 07/22/2009 - 07:06

Thanks Edison,


I also found additional information in my CP CCNA Portable Command Guide by Scott Empson.


Default behavior is platform dependent with the 2960 switches (I have a 2950 for my home lab) defaulting to dynamic auto. And this would mean to form a trunk the nieghboring port would need to be set at either "trunk" or "dynamic desirable"


My toughest challenge to to memorize what all the router/switch default behaviors are...

Edison Ortiz Wed, 07/22/2009 - 07:10

No need to memorize


Rack1SW1#sh run int f0/12

Building configuration...


Current configuration : 34 bytes

!

interface FastEthernet0/12

end


Rack1SW1#sh int f0/12 sw | i Administrative Mode

Administrative Mode: dynamic auto




pipemajor Wed, 07/22/2009 - 09:31

Thanks! Very handy show commands but...


I doubt I'd have access to that feature in an exam environment.

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