Refer to the exhibit. A network administrator is reviewing the configuration of switch S1. Which protocol has been implemented to group multiple physical ports into one logical link?

The configuration in the exhibit shows that the interfaces FastEthernet0/8 and FastEthernet0/9 on switch S1 have been configured with the channel-group 1 mode auto command. This command is used to configure the interfaces to negotiate an EtherChannel using Cisco’s Port Aggregation Protocol (PAgP).

PAgP is a Cisco-proprietary protocol used in the automatic creation of a fast EtherChannel link. The mode auto command enables PAgP only if the other side is interested in forming a PAgP EtherChannel. Since this is a Cisco-specific feature and the command explicitly refers to a channel group, which is associated with port channels, the correct answer is PAgP.