EtherChannel is a way to combine some phsycal link to be one logical link.

EtherChannel cisco, layer 2 (switch)

EtherChannel doesn't really aggregate the max speed of the link. if a logical link consists of four 100mps link, the max speed for a single communication is not 400mbps. it is still 100mbps. cisco has an algorithm for determining which path a traffic will use, it could be configure to depends on:

  • soure MAC address

  • destination MAC address

  • source and destination MAC address

  • source IP

  • destination IP

  • source and destination IP

  • source port

  • destination port

  • source and destination port

how we configure this usually depends on what the other end of the EtherChannel is.

every link participating in an EtherChannel must have the same configuration (same vlan / trunk, etc)

there are two EtherChannel protocols,

  • Link Aggregation Control Protocol (LACP), defined by IEEE. used when connecting to non cisco devices

  • Port Aggregation Control Protocol (PAgP), cisco-proprietary. used when connecting to cisco devices.

each of the protocol have 2 modes, LACP -> passive, active. PAgP -> auto, desirable. each of the mode show how the configured interface will negotiating the EtherChannel (you may think of these modes as the modes in trunk negotiation)

configuring etherchannel is different in CatOS and in IOS. to establish EtherChannel in IOS first you create a virtual etherChannel interface (interface Port-channel number) and configure this interface (vlan/trunk, etc). then you configure the physical interface that will be part of the virtual etherchannel interface ('channel-group number mode desirable|auto' enter this command at interface configuration level). remember that all of the physical interface must have identical configuration.

configuration in IOS

while in CatOS

set port name 3/1 Link #1 in Channel
set port name 3/2 Link #2 in Channel
set port name 3/3 Link #3 in Channel
set port name 3/4 Link #4 in Channel

set vlan 20 3/1-4

set port channel 3/1-4 mode desirable