When we configure etherchannel on switch cisco, we will to configure some protocol is pagp and lacp. What different at both ?

PAGP (Port Aggregation Protocol)

Is a cisco proprietary protocol also known as aggregation protocol. Pagp is allowed to creating etherchannel automatically with exchanging pagp packages between ports.  PAGP has two modes :

• Auto     :  In this mode, all interfaces is put in passive negotiation state, where these interface will be reply to the received packages though it doesn’t instigate pagp negotiation.
• Desirable   : In this mode, all interfaces is put in active negotiation state, where these negotiation with other interface is instigate by sending the aggregation packages.

LACP (Link Aggregation Protocol)

Also known as IEEE 802.3AD is a openstandard protocol that is used for ethernet link aggregation. This protocol will building dynamically etherchannel. It supported to transparent layer2 in addition to currently support in layer 3 mode for 5000 series and SRX devices.  LACP has two mode :

• Active : In this mode, all interfaces  or ports will be placed in active state negotiation, that is negotiation with other interface will be initiate by exchanging LACP packages.
• Passive :  In this mode, all interface or ports wil be placed in passive state negotiation, that is will be reply to received LACP packet though it doesn’t initiate by exchanging LACP packages.