Question on EtherChannels

Hey all

  I had a question regarding link-aggregation technology such as EtherChannels. I've been receiving conflicting information regarding this so any help to clear up the confusion would be much appreciated. The question is this: Does bundling the ports also aggregate the total bandwidth available to me? In other words, were I to bundle four fastethernet links at 100mb/sec would I be able to send out of that interface at speeds close to 400mb/sec? Or is link-aggregation strictly done for redundancy and spanning-tree purposes? I've heard different things from different sources, and I've also noticed that when you go on a switch and create a port-channel on four different fastethernet ports, issuing a show interface port-channel 1 commands still shows the total bandwidth on that link to be 100mb/sec.

 

Any help on this is appreciated. Thanks! 

Comments

  • Sort of. You do aggregate the bandwidth, but each flow has to go across one link and would not be able to exceed the speed of an individual link. How those flows get broken up is based on the port-channel load-balance method. This is configurable to some degree, but varies on some platforms as to what methods are available. In a case where the traffic crossing the link is mostly between the same two devices, you may not see any performance benefit from the aggregation.

    I would expect your port-channel to show the total bandwidth of all the links. If it doesn't, I'd suspect that some of the links aren't actually active in the bundle and I would start troubleshooting by looking at show etherchannel summary.

  • Yes your total bandwidth is 400MBps as you have access to 4 X 100MBps pipes. You can even choose how to loadbalance across the 4 links by follwing the steps here

    According to Cisco - This allows load sharing of traffic among the links in the channel as well as redundancy in the event that one or more links in the channel fail.

    In short it for Load sharing and redundancy

     

  • Yes your total bandwidth is 400MBps as you have access to 4 X 100MBps pipes. You can even choose how to loadbalance across the 4 links by follwing the steps here

    According to Cisco - This allows load sharing of traffic among the links in the channel as well as redundancy in the event that one or more links in the channel fail.

    In short it for Load sharing and redundancy

     

  • I just wanted to write up a thank you. I thought I had done it earlier and submitted it, but just checked on this thread and saw that it hasn't posted! :(

     

    THanks all for your answers, it helped me understand etherchannels a lot better!

  • It depends upon senario how you deployed your network. But to make it simple, If you have connected two switches directly into 4 ports, yes it is bundled to 400mbps link.

  • I agree with you as if we count two way, It's 800Mbps but with rational thinking, default speed of FE is 100mbps. But it can handle 200Mbps both ways.

     

    So, normally we say it's 400Mbps.

     

    :)

  • Correct. If we say throughput it's 200Mbps in FE port. But he is talking about speed so speed is always one way which is 100Mbps.

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