Link Aggregation Control Protcol (LACP)

LACP (Link Aggregation Control Protocol) is an open standards protocol (IEEE802.3ad) that allows multiple physical interfaces to be aggregated into one logical link.
Each logical link can contain up-to 8 physical members. All member ports within the bundle must have the same physical settings such as port type, speed and duplex.

Modes

Within LACP there are 2 modes available, Active and Passive.

  • Active – Within Active mode the switch tries to negotiate and form LACP with its neighbor.
  • Passive – Within Passive mode LACP is enabled but the switch waits for the neighbor to initiate the negotiation LACP.

Create LACP Bundle

Creating an LACP bundle is simple, you define the port-channel number onto each of the interfaces.

Switch(config-if)#interface range gi0/1-3
Switch(config-if-range)#channel-group 33 mode active
Creating a port-channel interface Port-channel 33

Show Commands

Below is an example of some of the common show commands.

Switch#sh lacp 33 neighbor 
Flags:  S - Device is requesting Slow LACPDUs 
        F - Device is requesting Fast LACPDUs
        A - Device is in Active mode       P - Device is in Passive mode     

Channel group 33 neighbors

Partner's information:

                  LACP port                        Admin  Oper   Port    Port
Port      Flags   Priority  Dev ID          Age    key    Key    Number  State
Gi0/1     SA      32768     fa16.3efa.dce3  24s    0x0    0x18   0x2     0x3D  
Gi0/2     SA      32768     fa16.3efa.dce3   6s    0x0    0x18   0x3     0x3D  
Gi0/3     SA      32768     fa16.3efa.dce3  16s    0x0    0x18   0x4     0x3D
Switch#sh lacp 33 counters 
             LACPDUs         Marker      Marker Response    LACPDUs
Port       Sent   Recv     Sent   Recv     Sent   Recv      Pkts Err
---------------------------------------------------------------------
Channel group: 33
Gi0/1       62     56       0      0        0      0         0     
Gi0/2       64     56       0      0        0      0         0     
Gi0/3       64     55       0      0        0      0         0

LACP provides the ability to define the number of active members within the bundle, in essence allowing you to have create hot-standby bundle members.

Switch(config)#int po33
Switch(config-if)#lacp max-bundle ?
  <1-8> Max number of ports to bundle in this Port Channel

Port Priority

Once you have configured the maximum ports allowed within a bundle the port priority can be configured. Setting priority’s on each of the ports provides you with greater control and allows you to determine what ports are first added to the bundle and what ports are added into the bundle in the event of interface failure.

Switch(config)#int gi0/3 Switch(config-if)#lacp port-priority 300 
Switch#sh lacp internal 
Flags:  S - Device is requesting Slow LACPDUs 
        F - Device is requesting Fast LACPDUs
        A - Device is in Active mode       P - Device is in Passive mode     

Channel group 33
                            LACP port     Admin     Oper    Port        Port
Port      Flags   State     Priority      Key       Key     Number      State
Gi0/1     SA      bndl      32768         0x18      0x18    0x2         0x3D  
Gi0/2     SA      bndl      32768         0x18      0x18    0x3         0x3D  
Gi0/3     SA      bndl      300           0x18      0x18    0x4         0x3D
Rick Donato
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