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Latest post 04-13-2017 10:19 AM by JoeM. 6 replies.
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  • 04-07-2017 12:25 PM

    • HubertW
    • Top 75 Contributor
    • Joined on 09-25-2013
    • Warsaw(PL)/Bratislava(SK)
    • Expert
    • Points 3,840

    Layer 2 Dynamic Switchports

    Hi,


     [ sw1 ](gig0/33)----(gig0/33)[ sw2 ]
    (gig0/37)
        |
        |
        |
        |
    (gig0/37)
     [ sw4 ]


    On sw1 two ports I set:

    "switchport mode dynamic desireble"


    On sw2 (gig0/33) and sw4 (gig0/37) I set:

    "switchport mode dynamic auto"


    The effect of above settings is:


    SW1#sh int gig0/37 switchport
    Name: Gi0/37
    Switchport: Enabled
    Administrative Mode: dynamic desirable
    Operational Mode: trunk
    Administrative Trunking Encapsulation: negotiate
    Operational Trunking Encapsulation: isl
    Negotiation of Trunking: On
    Access Mode VLAN: 1 (default)
    Trunking Native Mode VLAN: 1 (default)
    Administrative Native VLAN tagging: enabled
    Voice VLAN: none
    Administrative private-vlan host-association: none
    Administrative private-vlan mapping: none
    Administrative private-vlan trunk native VLAN: none
    Administrative private-vlan trunk Native VLAN tagging: enabled
    Administrative private-vlan trunk encapsulation: dot1q
    Administrative private-vlan trunk normal VLANs: none
    Administrative private-vlan trunk associations: none
    Administrative private-vlan trunk mappings: none
    Operational private-vlan: none
    Trunking VLANs Enabled: ALL
    Pruning VLANs Enabled: 2-1001
    Capture Mode Disabled
    Capture VLANs Allowed: ALL

    Protected: false
    Unknown unicast blocked: disabled
    Unknown multicast blocked: disabled
    Appliance trust: none
    SW1#



    and


    SW1#sh int gig0/33 switchport
    Name: Gi0/33
    Switchport: Enabled
    Administrative Mode: dynamic desirable
    Operational Mode: static access
    Administrative Trunking Encapsulation: negotiate
    Operational Trunking Encapsulation: native
    Negotiation of Trunking: On
    Access Mode VLAN: 1 (default)
    Trunking Native Mode VLAN: 1 (default)
    Administrative Native VLAN tagging: enabled
    Voice VLAN: none
    Administrative private-vlan host-association: none
    Administrative private-vlan mapping: none
    Administrative private-vlan trunk native VLAN: none
    Administrative private-vlan trunk Native VLAN tagging: enabled
    Administrative private-vlan trunk encapsulation: dot1q
    Administrative private-vlan trunk normal VLANs: none
    Administrative private-vlan trunk associations: none
    Administrative private-vlan trunk mappings: none
    Operational private-vlan: none
    Trunking VLANs Enabled: ALL
    Pruning VLANs Enabled: 2-1001
    Capture Mode Disabled
    Capture VLANs Allowed: ALL

    Protected: false
    Unknown unicast blocked: disabled
    Unknown multicast blocked: disabled
    Appliance trust: none
    SW1#


    What settings (defautl?) can influence on operational mode 'static access' vs 'trunk'?

    Thanks

    • Post Points: 35
  • 04-07-2017 4:17 PM In reply to

    • JoeM
    • Top 10 Contributor
    • Joined on 04-15-2012
    • Guadalajara, Mexico
    • Elite
    • Points 31,545

    Re: Layer 2 Dynamic Switchports

    HubertW:
     

    [ sw1 ](gig0/33)----(gig0/33)[ sw2 ]
    (gig0/37)
        |
        |
        |
        |
    (gig0/37)
     [ sw4 ]



    On sw1 two ports I set:

    "switchport mode dynamic desireble"


    On sw2 (gig0/33) and sw4 (gig0/37) I set:

    "switchport mode dynamic auto"

    SW1#sh int gig0/33 switchport
    Name: Gi0/33
    Switchport: Enabled
    Administrative Mode: dynamic desirable  <--this side good
    Operational Mode: static access  <--other side?

     Hi Hubert,

    I think you may want to double-check your settings on SW2 gi0/33.  

    My guess is that it is set to switchport mode access .

    • Post Points: 5
  • 04-08-2017 11:21 PM In reply to

    Re: Layer 2 Dynamic Switchports

    DTP only works if the VTP domain names match

    So i assume they match between SW1 and SW4 and differ between SW1 and SW2

    If DTP fails it falls back to "access" mode

    • Post Points: 35
  • 04-09-2017 6:18 PM In reply to

    • JoeM
    • Top 10 Contributor
    • Joined on 04-15-2012
    • Guadalajara, Mexico
    • Elite
    • Points 31,545

    Re: Layer 2 Dynamic Switchports

    I agree with Johannes.   Nice call.  This would be a perfect exam question.

     

    • Post Points: 5
  • 04-09-2017 6:23 PM In reply to

    • JoeM
    • Top 10 Contributor
    • Joined on 04-15-2012
    • Guadalajara, Mexico
    • Elite
    • Points 31,545

    Re: Layer 2 Dynamic Switchports

    But not sure about what Hubert is doing...because in my lab...there is a clear log error on both sides. If he does not see this, then I go back to my original answer. ;-)

     %DTP-5-DOMAINMISMATCH: Unable to perform trunk negotiation on port Gi0/0 because of VTP domain mismatch.

    • Post Points: 5
  • 04-13-2017 2:59 AM In reply to

    • HubertW
    • Top 75 Contributor
    • Joined on 09-25-2013
    • Warsaw(PL)/Bratislava(SK)
    • Expert
    • Points 3,840

    Re: Layer 2 Dynamic Switchports

    Hi,

     

    yes, VTP domain is the problem

     

    Thanks

    • Post Points: 20
  • 04-13-2017 10:19 AM In reply to

    • JoeM
    • Top 10 Contributor
    • Joined on 04-15-2012
    • Guadalajara, Mexico
    • Elite
    • Points 31,545

    Re: Layer 2 Dynamic Switchports

    Thanks Hubert for updating us.   Nice little puzzle. 

    • Post Points: 5
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