CCNA - Switch Vlan DTP - trunk encapsulation negotiate

[mozmarr124]

Trying to find out in what circumstances, why, would 2 trunk ports 'negotiate' the trunking protocol (ISL or dot1q)?

From what I have read, if ISL and 802.1q are both supported, ISL is preferred  - so why negotiate?

If only 802.1q is supported then the negotiate command doesnt even exist?

In general - what is the point of the negotiate option when choosing the trunking protocol?

Any help to clear this up appreciated

[Georg Pauwen]

Hello,

the post linked below has an excellent explanation of why and when to use DTP:

https://community.cisco.com/t5/switching/why-dtp-is-used/td-p/1377495

[mkazam001]

you can either manually configure trunk links between the switches for ISL or 802.1q or leave DTP to negotiate the trunk.

DTP was intended to make less work for administrators.

it is true that if both ends support both protocols isl is favoured.

it is recommended to not leave much to auto negotiation, so best to configure the trunk ports manually:

eg. switchport mode trunk

      switchport nonegotiate

      switchport trunk encapsulation dot1q

regards, mk