Which two modes are used by PAgP for EtherChannel configuration?

PAgP, or Port Aggregation Protocol, is a Cisco proprietary protocol used to automate the creation of EtherChannels by allowing switches to negotiate their configurations. Within PAgP, two specific modes facilitate this negotiation process: Desirable and Auto.

In the Desirable mode, a switch actively attempts to form an EtherChannel by sending PAgP packets to its neighbor. It can initiate the formation of an EtherChannel if the other switch is set to a compatible mode.

In the Auto mode, a switch is configured to automatically respond to PAgP packets but does not initiate any requests to form an EtherChannel. This mode allows the switch to participate in an EtherChannel if the neighboring switch is in a Desirable state, but it will not actively seek to establish the link.

This negotiation process allows for more dynamic and adaptable network configurations, enhancing the ability of network administrators to ensure redundancy and increased bandwidth without requiring manual intervention for each link in the EtherChannel.

The other modes mentioned in the other choices relate to different protocols or configurations that do not apply to PAgP specifically, such as LACP (Link Aggregation Control Protocol), which uses Active and Passive modes, or manual configurations that do not support the automated negotiation that PAgP provides.