When Switch A's port is configured to access mode from trunk mode, Switch B's port stays in trunk mode.

Switch A is DTP disabled (#switchport nonegotiate). Switch B has default configuration which is dynamic auto and DTP enabled.

Is this normal?

  • 3
    a) what are the types and IOS versions of each switch? b) include the configuration of the ports (show run int xxx) c) are you using VTP? As a general rule, never trust DTP.
    – Ricky
    May 18, 2015 at 22:13
  • 2
    DTP is almost as bad as VTP. It's worth trying it out in a lab, but disabling it will save you in the future. Plus not all Cisco gear supports it (NX-OS...) and it is a security hole (user can DTP-negotiate an edge port to a trunk, allow access to all vlans).
    – cpt_fink
    Jun 5, 2015 at 2:28

2 Answers 2


Depending on when the commands were typed in, this sounds like the expected behaviour. If Switch A were plugged into Switch B, and Switch A moved to the trunk state, then DTP on Switch B would have negotiated trunk mode.

This is how DTP normally negotiates the interface mode:

Table 3-8 DTP Negotiated Interface Modes

                Dynamic       Dynamic     Trunk        Access
                Auto          Desirable

Dynamic Auto    Access        Trunk       Trunk        Access <-- Should be here

Dynamic         Trunk         Trunk       Trunk        Access

Trunk           Trunk         Trunk       Trunk        Limited 

Access          Access        Access      Limited      Access

Cisco Press, Cisco Networking Academy's Introduction to VLANs, Table 3-8

However, if you disabled DTP on Switch A, then Switch B would have no further knowledge of any changes in interface changes on Switch A. So moving Switch A to access will not be conveyed to Switch B, as it would have normally expected.

If you reset the connection between them, Switch B would have never changed it's mode to trunk and remain in access mode. Then you'd be having the total opposite problem (Switch B not turning into a trunk).

  • 1
    It'll change after timeout of Dynamic Trunk timeout time.
    – Ron Vince
    Jun 5, 2015 at 7:22

DTP by default has 300 seconds of Dynamic Trunk timeout. So, Switch B will change its port operational mode to "static access" if it will have not received any DTP advertisement to trunk in the next 300 seconds [after it changes the port operational mode to "static access" or since the receive of the DTP advertisement to trunk].

I tested and the Switch B's port operational mode was changed from "trunk" to "static access" after 300 seconds.

Note: The statement in [ ] is not confirmed. It is supposed to be either one.

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