5 Replies Latest reply: Mar 14, 2014 12:45 AM by anicet RSS

    switchport nonegotiate


      Hi ,


      If i configure a switch to use switchport mode trunk with no negotiate command , would that form a trunk with the other end switch which is configured to act in dynamic mode auto ? Also I am looking for the reason, how could switches configured as "trunk" / ON mode , could form trunk even when we disable DTP on them. What kind of communication happens between the switches in trunk mode to let them bring up a trunk link,  when dtp frames are disabled ?



      - Baks

        • 1. Re: switchport nonegotiate

          When you put a switchport into trunking mode, it will trunk and it will try to negotiate. Dynamic auto will wait for a request to trunk, so if the other side is set to trunk, a trunk will form. If you disable negotiating by issuing the switchport nonegotiate command, both sides will need to be set to trunk in order for a successful trunk to be created.


          When both sides are configured to trunk, no negotiation is needed. A trunk will be formed based on the manual configuration of the switches and the switchports.




          • 2. Re: switchport nonegotiate

            DelVonte nailed it.....


            When you configure nonegotiate, you're disabling DTP - but not the port's ability to function as a trunk.  With DTP disabled the port will behave as dictated by the manual configuration you enter.

            • 3. Re: switchport nonegotiate

              Thanks for the information Guys.


              So to let the switches to bring up a trunk, given a condition that one of the switch is configured for dynamic mode (auto / desirable), it requires the dtp to be enabled (on both the switches) irrespective of the mode (either trunk / auto / desirable)  that is configured on far-end switch. Did i grasp it correctly ?



              - Baks

              • 4. Re: switchport nonegotiate

                In order to negotiate a trunk, both switches do need to have DTP enabled, but If your switchport is in dynamic auto mode, the other side needs to be in either dynamic desirable or trunk in order for a trunk to form successfully. Other than that, you are correct.




                • 5. Re: switchport nonegotiate

                  If i get you, you are asking 2 questions which are as follow:

                  1-Will 2 switches form a trunk link when "trunking" is configured statically with "nonegotiate" option on one side and when "dynamic auto" is configured on the other side?

                  2-How 2 switches on which trunking is configured statically with DTP disabled can form a trunk link?


                  for the 1st question, trunking wont be formed between both switches because in "dynamic auto" mode, the switch's port can never initiate any trunking config and the switch configured statically to trunk plus the "nonegiate" option also is not going to initiate any trunking  bcz of the "nonegotiate"option which disables DTP.To enable trunking in this case, static trunking should be configured on the other switch with this command"switchport mode trunk" instead of "switchport mode dynaamic auto"

                  For the 2nd question, yes trunking can be formed between both switches even though "nonegotiate" option has been added..it doesnt really matter bcause the switches have already been configured to trunk statically so DTP is not needed in that case..

                  Hope i answered to ur questions and plz if am wrong let me know ths..