LACP- LINK AGGREGATION CONTROL PROTOCOL.

Link Aggregation Control Protocol is used for logically bundle many physical links and convert into a single logical medium.

For example:

If the traffic between core and access switch is high, But some time we might have a single physical connectivity between the switches, It might not be capable of handling the high load traffic so we must connect two are more cable and make them single medium(work like single wire).    

One more  protocol name.

PAGP port aggregation protocol which is Cisco proprietary. 


Switch1 :
==========


interface Port-channel1
!
interface GigabitEthernet0/0
 negotiation auto
 channel-group 1 mode active
!
interface GigabitEthernet0/1
 negotiation auto
 channel-group 1 mode active


Switch 2:
=========


interface Port-channel1
!
interface GigabitEthernet0/0
 negotiation auto
 channel-group 1 mode active
!
interface GigabitEthernet0/1
 negotiation auto
 channel-group 1 mode active


Verification output:
====================

SW1#show etherchannel 1 detail
Group state = L2
Ports: 2   Maxports = 4
Port-channels: 1 Max Port-channels = 4
Protocol:   LACP
Minimum Links: 0


                Ports in the group:
                -------------------
Port: Gi0/0
------------

Port state    = Up Mstr Assoc In-Bndl
Channel group = 1           Mode = Active          Gcchange = -
Port-channel  = Po1         GC   =   -             Pseudo port-channel = Po1
Port index    = 0           Load = 0x00            Protocol =   LACP

Flags:  S - Device is sending Slow LACPDUs   F - Device is sending fast LACPDUs.
        A - Device is in active mode.        P - Device is in passive mode.

Local information:
                            LACP port     Admin     Oper    Port        Port
Port      Flags   State     Priority      Key       Key     Number      State
Gi0/0     SA      bndl      32768         0x1       0x1     0x1         0x3D

Partner's information:

                  LACP port                        Admin  Oper   Port    Port
Port      Flags   Priority  Dev ID          Age    key    Key    Number  State
Gi0/0     SA      32768     5000.0001.8000  27s    0x0    0x1    0x1     0x3D

Age of the port in the current state: 0d:00h:03m:35s

Port: Gi0/1
------------

Port state    = Up Mstr Assoc In-Bndl
Channel group = 1           Mode = Active          Gcchange = -
Port-channel  = Po1         GC   =   -             Pseudo port-channel = Po1
Port index    = 0           Load = 0x00            Protocol =   LACP

Flags:  S - Device is sending Slow LACPDUs   F - Device is sending fast LACPDUs.
        A - Device is in active mode.        P - Device is in passive mode.

Local information:
                            LACP port     Admin     Oper    Port        Port
Port      Flags   State     Priority      Key       Key     Number      State
Gi0/1     SA      bndl      32768         0x1       0x1     0x2         0x3D

Partner's information:

                  LACP port                        Admin  Oper   Port    Port
Port      Flags   Priority  Dev ID          Age    key    Key    Number  State
Gi0/1     SA      32768     5000.0001.8000  25s    0x0    0x1    0x2     0x3D

Age of the port in the current state: 0d:00h:03m:35s

                Port-channels in the group:
                ---------------------------

Port-channel: Po1    (Primary Aggregator)

------------

Age of the Port-channel   = 0d:00h:03m:46s
Logical slot/port   = 16/0          Number of ports = 2
HotStandBy port = null
Port state          = Port-channel Ag-Inuse
Protocol            =   LACP
Port security       = Disabled
Load share deferral = Disabled

Ports in the Port-channel:

Index   Load   Port     EC state        No of bits
------+------+------+------------------+-----------
  0     00     Gi0/0    Active             0
  0     00     Gi0/1    Active             0

Time since last port bundled:    0d:00h:03m:35s    Gi0/1



SW1#show etherchannel 1 summary
Flags:  D - down        P - bundled in port-channel
        I - stand-alone s - suspended
        H - Hot-standby (LACP only)
        R - Layer3      S - Layer2
        U - in use      N - not in use, no aggregation
        f - failed to allocate aggregator

        M - not in use, minimum links not met
        m - not in use, port not aggregated due to minimum links not met
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port

        A - formed by Auto LAG


Number of channel-groups in use: 1
Number of aggregators:           1

Group  Port-channel  Protocol    Ports
------+-------------+-----------+-----------------------------------------------
1      Po1(SU)         LACP      Gi0/0(P)    Gi0/1(P)