Channel Bonding: link aggregation across 2 switches

Discussion in 'Linux Networking' started by js, Aug 31, 2006.

  1. js

    js Guest

    There are 2 switches on the data centre which is a switch managed by the
    hosting company. Our servers have dual NICs in them and they are currently
    configured using active-backup. Thus, only one slave is active at any time.

    AFAIK, the switch is meshed together to provide redundant connections.

    In this scenario, is it possible to have have link aggregation across 2
    different switches that are meshed together ?
    js, Aug 31, 2006
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  2. There are a variety of ways. I personally prefer doing this at layer 3
    (IP layer), especially if your switches can also route at wire speed.

    Basically, you assign each link an IP address and you assign the
    machine a third IP address. You then advertise a route to the third IP
    address over each link and arrange for traffic to be shared over
    equal-cost links.

    David Schwartz, Aug 31, 2006
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  3. That depends on the capabilities of the switches.

    A $100 switch can't do anything of any real intelligence, but a $5000
    one can.
    Jeroen Geilman, Sep 4, 2006
  4. js

    js Guest

    Assuming the switch does support it, is there anything special that needs to
    be done on setting up the bonding interface ? Or is the work done the same
    compared to setting up link aggregation of multiple NICs on just one
    switch ?
    js, Sep 5, 2006
  5. You just "bond" or "team" or "whatever" the NICs as you would normally -
    whether two bonded NICs connect to one switch or to two different ones
    should not matter as long as those switches communicate that fact to
    each other.

    You do need enough bandwidth *across* the mesh to support this, however.

    If the link connecting the switches is slower than the resultant
    bandwidth of 2 bonded NICs, the bottleneck will land squarely on that
    link, and bonding the client NICs serves no purpose whatsoever.

    Remember that end-to-end traffic will still need to go to *one*
    endpoint, which is connected to either one switch, or the other.

    Unless *all* systems are connected this way, in which case you could
    (theoretically) turn a 1 gbit switching matrix into a 2 gbit one :)

    So "the switch supports it" depends on two factors:
    1. do they support trunking of bonded channels across the mesh link ?, and
    2. are they themselves connected by sufficient bandwidth to make this
    scheme even sensible ?

    I know for a fact that most Cisco switches can do this.


    Jeroen Geilman, Sep 6, 2006
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