Exam 200-301 topic 1 question 243 discussion

B and C are correct

Actually B is correct as well

ANSWER: B Most of you are confusing Etherchannel link setup with CDP trunking setup. Although they interconnect at some point and they use DESIRABLE/AUTO in both settings, these are two different things.

Just like B is correct, C is also correct when one switch is already in trunk or dynamic desirable mode then other switch doesnt have to be dynamic desirable mode(If it is dynamic desirable mode it will establish trunk port for sure), switch can be in dynamic auto mode where switch can passively wait for the other side to initiate trunking process

Setting dynamic auto on the local switch will allow it to passively become a trunk when the other side initiates trunk negotiation.

If the switch is old model: -Default mode is dynamic desirable and a command wouldn't be needed as it would already form a trunk, this scenario discards B and C. If the switch is new: -Default mode is dynamic auto and it would also form a trunk without the need of an additional command. This discards option C as it makes no sense to issue an existing command and leave the option B. Also the question says "must form a trunk".

Summary The table below summarizes the possible states: Port 1 Port 2 Trunk Formed? Trunk Trunk Yes Trunk Dynamic Desirable Yes Trunk Dynamic Auto Yes Trunk Access No Dynamic Desirable Dynamic Desirable Yes Dynamic Desirable Dynamic Auto Yes Dynamic Auto Dynamic Auto No Dynamic Desirable Access No Dynamic Auto Access No Nonegotiate Trunk Yes Nonegotiate Nonegotiate Yes

you guys how you vote for B and in the question this hint : The neighboring switch is set to trunk or desirable mode ... means we have already desirable mode, the other neighboring must have Auto or Active ... correct me if im wrong

B. configure switchport mode dynamic desirable: This command sets the local switchport to negotiate the trunk link actively. It will initiate negotiations if the neighboring switch is set to desirable, and it will accept negotiations if the neighboring switch is set to trunk mode. This is the correct choice in this scenario. C. configure switchport mode dynamic auto: This command sets the local switchport to negotiate the trunk link passively. It will accept negotiations if the neighboring switch is set to desirable mode but will not initiate negotiations. This is not the best choice in this scenario.

When a Cisco switch is configured in "desirable" mode for a particular trunk negotiation (trunking) protocol, the state of the other switch must be configured accordingly to ensure a compatible and stable trunk configuration. If a switch is configured as "desirable", this means that it is willing to form a trunk if the other side is also configured to form a trunk (i.e., "desirable", "auto", or "on"). So for best practices: 1. **If both switches are under your control:** - You can configure the other switch in "desirable" mode to ensure that both sides are configured to form an active trunk. 2. **If only one switch is under your control:** - Configure the other switch to "desirable", "auto", or "on", depending on your trunk configuration policy and network needs. - "Desirable" if you want the trunk to be formed whenever possible. - "Auto" if you want the switch to accept trunk formation if the other side is configured to form a trunk. - "On" if you want the trunk to always be formed, regardless of the configuration on the other side. Always ensure that both sides of the trunk link are configured compatible to avoid interoperability issues and ensure network stability.

When connecting two switches via a trunk link, it's crucial to decide the switchport mode settings. Given that the neighboring switch is set to trunk or desirable mode, you should configure the local switch to a mode that enables successful negotiation. Modes dynamic desirable and dynamic auto will try to convert the link to a trunk link if the neighboring port is set to trunk, dynamic desirable, or dynamic auto. Since the neighboring switch is already set to desirable mode, which actively attempts to convert the link into a trunk, you should configure switchport mode dynamic desirable (option 2). This way, the local switch will also actively attempt to convert the link to a trunk link, which will ensure a successful trunk link establishment as both sides are actively negotiating for it.

According to chatgpt is B

Although both B and C are correct, I think here the logic here is granting the "least privileges". By setting the switch to dynamic auto it will only form a trunk with another switch set in trunk or dynamic desirable and NOT in dynamic auto (2 conditions, as stated in the question). By setting it to dynamic desirable it will form a trunk with another switch set to desirable OR auto OR trunk (3 conditions)

• Dynamic Auto — Makes the Ethernet port willing to convert the link to a trunk link. The port becomes a trunk port if the neighboring port is set to trunk or dynamic desirable mode. This is the default mode for some switchports. • Dynamic Desirable — Makes the port actively attempt to convert the link to a trunk link. The port becomes a trunk port if the neighboring Ethernet port is set to trunk, dynamic desirable or dynamic auto mode. B and C are correct

Both answers are correct very confusing: switchport mode dynamic desirable: Makes the interface actively attempt to convert the link to a trunk link. The interface becomes a trunk interface if the neighboring interface is set to trunk, desirable, or auto mode.

Going with B

its b because auto & auto -> none