# Etherchannel on Cisco IOS Catalyst Switch **URL:** https://forum.networklessons.com/t/etherchannel-on-cisco-ios-catalyst-switch/1084 **Category:** Lessons Discussion **Created:** [December 26, 2016, 10:31pm UTC](https://forum.networklessons.com/t/etherchannel-on-cisco-ios-catalyst-switch/1084 "2016-12-26T22:31:15Z") **Posts on this page:** 1 **Showing post:** 107
### Author: ![lagapidis](https://cdn-forum.networklessons.com/user_avatar/forum.networklessons.com/lagapidis/32/4949_2.png) [@lagapidis](https://forum.networklessons.com/u/lagapidis) #### Post date: [January 22, 2020, 6:39am UTC](https://forum.networklessons.com/t/etherchannel-on-cisco-ios-catalyst-switch/1084/107 "2020-01-22T06:39:19Z")
Hello Po When we talk about load balancing between physical connections of etherchannels, we must use some criteria to determine which physical link a particular frame will go over. Take a look at the following diagram: ![image](https://cdn-forum.networklessons.com/uploads/default/original/2X/0/0c9e1c7e1a2361dac98b30b79ed9a95985eed5a7.png) Devices in Network A will be communicating with devices in Network B. Each of the frames traversing the link will have a source and destination MAC, and at Layer 3, will have a source and destination IP address. Remember first of all that load balancing must be employed on a per direction basis. This means that for the above topology, you must configure the load balancing that will be employed **for each direction**. For traffic from SW1 to SW2, you configure the load balancing on SW1. For traffic from SW2 to SW1, you configure the load balancing on SW2. Now let’s say you have 60 hosts on Network A, and you have a single host, say a default gateway, on Network B. Let’s take a look at traffic going from Network A to Network B. If load balancing by source MAC address is configured, then the traffic going from all the hosts on Network A over the etherchannel, will be load balanced well. Specifically, traffic from 10 hosts will use each single physical connection. (60 source MAC addresses, 6 physical links). That’s good right? But what if you used the destination MAC as the criteria? There’s only one destination MAC on Network B, which is the default gateway. So whenever SW1 sees that destination MAC, it will always send the traffic over a single physical link. So the source and destination MAC and IP addresses used for the algorithm are those found within the frame/packet for the particular direction of travel of that packet. You might find these posts helpful as well: > [@Etherchannel on Cisco IOS Catalyst Switch](https://forum.networklessons.com/t/etherchannel-on-cisco-ios-catalyst-switch/1084/97): > > Hello team, I need help. According a topology below a single server is connected via EtherChannel to a single Layer 2 switch. A router is the default gateway to the server. I think in this case on the switch traffic flow from the router should be load balanced based on the destination addresses (MAC or IP). Let me know please if I’m wrong. Another scenario. We have multiple computers. Which EtherChannel load balancing methods on the Layer 2 switch make optimal use of the redund… > [@Etherchannel on Cisco IOS Catalyst Switch](https://forum.networklessons.com/t/etherchannel-on-cisco-ios-catalyst-switch/1084/98): > > Hello Boris These are excellent examples that very appropriately show the distinction between the various load balancing methods and the scenarios for which they are useful. Remember first of all that load balancing must be employed on a per direction basis. This means that if you have a topology like this: SW1===SW2, then you must configure the load balancing that will be employed for each direction. For traffic from SW1 to SW2, you configure the load balancing on SW1. For traffic from S… I hope this has been helpful! Laz --- _[View the full topic](https://forum.networklessons.com/t/etherchannel-on-cisco-ios-catalyst-switch/1084)._