EtherChannel Tutorial

EtherChannel Configuration

To assign and configure an EtherChannel interface to an EtherChannel group, use the channel-group command in interface mode: channel-group number mode { active | on | {auto [non-silent]} | {desirable [non-silent]} | passive}
For example we will create channel-group number 1:

If a port-channel interface has not been created before using this command, it will be created automatically and you will see this line: “Creating a port-channel interface Port-channel 1”. In this example, we will create an EtherChannel via LACP between SwA & SwB with the topology shown below:

That is all the configuration for the EtherChannel to work well on both switches. We can verify with the “show etherchannel <port-channel number> port-channel” or “show etherchannel summary” command.

SwA# show etherchannel 1 port-channel  
     Port-channels in the group:   
     ----------------------------
 Port-channel: Po1
 Age of the Port -channel   = 0d:00h:02m:37s 
 Logical slot/port   = 2/1          Number of ports = 2 
 GC                  = 0x00010001      HotStandBy port = null  
 Port state          = Port-channel Ag -Inuse  
 Protocol            =   LACP
 Port security       = Disabled  
  
 Ports in the Port-channel:  
  
 Index   Load   Port     EC state        No of bits  
 ------+------+------+------------------ +----------- 
   0     00     Fa0/0    Active                  0  
   0     00     Fa0/1    Active                  0  
  
 Time since last port bundled:    0d:00h:02m:27s    Fa0/1

The “show etherchannel number port-channel” command can be used to display information about a specific port channel (in this case port-channel 1). From the command above we can see Port-channel 1 consists of Fa0/0 & Fa0/1 and they are in Active state.

 SwA# show etherchannel 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      f - failed to allocate aggregator 
  
          M - not in use, minimum links not met  
          u - unsuitable for bundling  
          w - waiting to be aggregated 
          d - default port 
  
 Number of channel-groups in use: 1 
 Number of aggregators:           1 
  
 Group  Port-channel  Protocol    Ports 
 ------+------------- +-----------+-----------------------------------------------  
 1      Po1(SU)         LACP      Fa0/0(P)   Fa0/1(P) 

The “show etherchannel summary” can be used to simply display one line of information per port-channel. In this case we learn from the last line that Group 1 uses LACP. This is a Layer 2 EtherChannel (symbolized by “SU”, in which “S” means “Layer2” & “U” means this port-channel is up.

EtherChannel Load-Balancing

EtherChannel load-balances traffic among port members of the same channel. Load balancing between member interface is based on:
+ Source MAC address
+ Destination MAC address
+ Source IP address
+ Destination IP address
+ Combination of Source and Destination MAC address
+ Combination of Source and Destination IP address

Note: Some old switch/router flatforms do not support all the load-balancing methods above. To configure load-distribution method, use the command port-channel load-balance under global configuration mode. For example to load-balance based on destination MAC use the command:

How the router/switch load-balances traffic among member interface is out of the scope of this article. For more information about EtherChannel load-balancing please visit http://www.cisco.com/en/US/tech/tk389/tk213/technologies_tech_note09186a0080094714.shtml#topic1.