Cisco DTP (Dynamic Trunking Protocol) Negotiation

This topic is to discuss the following lesson:

Thanks Rene very useful

Dear René,

Is it to avoid a security issue that we disable DTP ? If someone bring a rogue switch and plug it et voilà we negociate a trunk ?

Thks,

Prince

 

Hi Prince,

That’s correct, this could be dangerous if your interface is configured for “dynamic auto” or “dynamic desirable”.

If you configured the interface in static “access” or “trunk” then negotiatin can’t change it anymore but you are still sending DTP packets which is a bit pointless, better to just disable them.

Rene

Thanks for the reply René,

 

Prince

Rene,

Watching you switching videos and I like the background of your terminal. Tale me, which terminal program and font are you using. I would like to use such a background.

 

Hi Jesse,

Which video did you see?

For a long time I used Linux Mint (Mate edition) with the mate-terminal to record these videos. It was the default font, not sure which one that was.

Nowadays I use secureCRT configured to use the same colors as Pycharm’s darcula (I liked their colors):

Here’s a screenshot of what my SecureCRT looks like:

I’m not sure if this is the best for videos but it’s easy on the eyes, even after hours of hardcore Cisco console work :slight_smile:

Rene

Very good information.

thank you
Rene
your wonderful

You are welcome Hussein.

Hi Rene,

Can you explain me what does it mean Trunking negotiation is ON does it means that this particular mode is set to send DTP frames . to the my knowledge only Dynamic desirable and ON mode will send out DTP frames and other modes are doesn’t (Dynamic Auto and Access)

Hello Ankit

When we say that DTP negotiation is ON, it means that the port is in a state where, if the proper DTP packets are sent/received, the port may change its trunking functionality. Negotiation is ON in the following states: Dynamic Desirable, Dynamic Auto or Trunk.

DTP negotiation is OFF when a port is in one of the following states: Access or Non-negotiate.

As for the exchanging of DTP frames, these are sent when a port is in the following states: Dynamic Desirable and Trunk.

DTP frames are NOT sent when a port is configured as Dynamic Auto, Non-negotiate or Access.

So, even if a port is in Dynamic Auto and doesn’t send DTP frames, it is still considered Negotiation ON because it can be affected by the DTP frames it receives.

I hope this has been helpful!

Laz