Stacking 2 Cisco 2970G switches

Posted on 2011-04-26
Last Modified: 2012-05-11
Is it possible to use 2 sfp ports to daisy chain a pair of 2970G switches and load-balance the 2 gig ports to allow for a full 2GB of through-put between the 2 devices?

Or I am limited to using a single sfp port and 1gb of throughput?
Question by:mcrouch1

    Expert Comment

    Technically with one fiber you get 2gb of through-put.  But if you connect two fibers between the switches then PagP should create an etherchannel for you and they should load balance and give you 4gb between the switches.  You can check by doing a Show pagp on the switch after you make the connection.  It should show the channel group number.  

    Author Comment

    Do you have any examples of the config by chance?
    LVL 8

    Expert Comment

    doing this will only help you if your traffic between the switches comes from a random mix of mac addresses. the switch determines which link to send the packet over based on source and/or destination mac address. if your traffic is all between a few servers, then you most likely wont see even balance of traffic, but you should find somewhat better than only using one link.
    LVL 26

    Accepted Solution

    Assuming you will be carrying vlans across these fibers:

    interface Port-channel 1
    switchport trunk encapsulation dot1q
    switchport mode trunk

    For SFP's (Do this for ever SFP interface you want part of Port channel 1)

    interface x/x
    switchport trunk encapsulation dot1q
    switchport mode trunk
    channel-group 1 mode on

    You don't need PaGp. Just manually enable the port channels. PaGP or LACP is  used you want etherchannels to be created automatically, depending on the configuration of the switch on the other end of the link aggregate.


    Author Comment

    ok guys thank you.  I will go ahead and try this with the 2970G's.  My servers and power users will be on the main switch and the people that don't require the network as much will be on the daisy chained switch.

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