Cisco Certified Network Associate (CCNA) Practice Exam

Which command is used to create a dynamic Port Aggregation Protocol EtherChannel?

1. (config-if)#channel-group CHANNEL GROUP NUMBER mode desirable

2. (config-if)#channel-group CHANNEL GROUP NUMBER mode manual

3. (config-if)#channel-group CHANNEL GROUP NUMBER mode active

4. (config-if)#channel-group CHANNEL GROUP NUMBER mode auto

The correct answer is: (config-if)#channel-group CHANNEL GROUP NUMBER mode desirable

The command to create a dynamic Port Aggregation Protocol (PAgP) EtherChannel uses the "mode desirable" setting. When this mode is configured, the interface actively initiates the formation of the EtherChannel. It sends PAgP packets to negotiate the link aggregation with other interfaces. If the neighboring interface is also configured to form an EtherChannel (whether in "auto" or "desirable" mode), the two interfaces will form an EtherChannel, allowing for increased bandwidth and redundancy through link aggregation. Choosing "mode desirable" is significant because it enables proactive negotiation, enhancing the likelihood of forming the EtherChannel as long as the other side is compatible. This is essential for smooth network operations where additional links can provide better load balancing and fault tolerance. In contrast, the other options utilize different modes. "mode manual" does not initiate any negotiation and requires the opposite end to be configured similarly to establish an EtherChannel. "mode active" is specific to Link Aggregation Control Protocol (LACP), making it applicable for a different context than PAgP. Lastly, "mode auto" allows the interface to passively wait for negotiation invitations but does not initiate them, making it less dynamic compared to "mode desirable."