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the on mode still negotiable (send/receive DTP) until i set it no negotiate so what is the Difference between on and Desirable.

please give an example :))

  • Did any answer help you? If so, you should accept the answer so tht the question doesn't keep popping up forever, looking for an answer. Alternatively, you could post and accept your own answer. – Ron Maupin Dec 22 '18 at 3:17
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I think you are confusing DTP with PAgP. DTP doesn't have a switchport mode on, while PAgP has channel-group <num> mode on. DTP is always on for a switch port unless you turn it off with switchport nonegotiate.

The DTP commands are:

  • switchport mode trunk - initiates DTP (always trunk)
  • switchport mode access - initiates DTP (never trunk)
  • switchport mode dynamic desirable - initiates and listens for DTP (negotiate trunk)
  • switchport mode dynamic auto - listens for DTP (negotiate trunk)
  • switchport nonegotiate - disables DTP
  • switchport trunk encapsulation <encap> - disables DTP trunk encapsulation negotiation
  • thanks for replying Ron, #switchport mode trunk - this is on mode (unconditional trunk) this is initiates DTP as you said, so it keeps negotiation with other port until i set it to #sw nonegotiate so what is the difference between Desirable and on let me make it clear to you Desirable send/receive DTP and after all it will be Trunk on send/receive DTP (as long as i didn't configure it nonegotiation) and after all it will be Trunk – ebnrdwan Sep 6 '15 at 23:39
  • switchport mode trunk still initiates DTP to tell the other side that it will only trunk. The only way to stop the DTP messages is to use switchport nonegotiate. – Ron Maupin Sep 6 '15 at 23:41
  • yeah dude i know,, let me make it clear to you>>>(1) Desirable>>[[ send/receive DTP and after all it will be Trunk ]]] ...........>>(2) on >> [[send/receive DTP (as long as i didn't configure it nonegotiation) and after all it will be Trunk ]]............... so what is the difference – ebnrdwan Sep 6 '15 at 23:44
  • As I said, it's because it is sending DTP to tell the other side that it will only trunk since it doesn't know what mode the other side is in (the other side may listening and depending on DTP to set its mode). On older switches, it may also need to negotiate the encapsulation via DTP. The switchport nonegotiate is there to disable DTP because none of the other settings will disable DTP since they all use it for one thing or another. DTP is a two-sided thing. – Ron Maupin Sep 6 '15 at 23:53
  • i got it, Thanks so much Ron, i appreciate your interest – ebnrdwan Sep 7 '15 at 0:08

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