Link aggregation for dumb 10/100 switches

Discussion in 'Linux Networking' started by Chris Adams, Nov 10, 2003.

  1. Chris Adams

    Chris Adams Guest


    I'm wondering if Linux has any support for anything like this (or if
    anyone's ever thought of something like this before!):

    In my hypothetical situation I've got a gigabit switch, a 10/100 switch
    which has no link aggregation support and a linux box with a gigabit NIC and
    2 100mb nics. I want the 10/100 switch to have a greater uplink bandwidth
    than 100mbit/sec but it's got no gigabit ports and no aggregation support,
    so I was thinking that by plugging both my linux box's 100mbit nics into it
    and plugging its gigabit nic into the gigabit switch it's possible to set up
    some kind of bridge that makes the switch think that some MAC addresses
    exist on one port and some on the other.

    What would happen is that when a frame arrives on the gigabit interface that
    is destined for the 100mb switch, it is forwarded onto either of the 2
    100mbit interfaces, depending on its mac. The linux box would need to
    remember which mac address is sent to which interface. It would create a
    pseudo-aggregated link without needing any real intelligence in the 100mb
    switch. Although the maximum bandwidth to any one mac address would be
    100mbit, the other nic would be available for traffic to (half of the) other

    Broadcast packets would have to be completely ignored by one nic to prevent
    duplicate broadcasts, but that's about the only real issue I can see with
    this setup.

    Is there a way to do this under linux that doesn't involve iptables? Or do I
    need to get my hands dirty and write it myself :)

    Thanks in advance,
    - Chris.
    Chris Adams, Nov 10, 2003
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  2. Chris Adams

    Chris Adams Guest

    Would ebtables allow me to do this?
    Chris Adams, Nov 10, 2003
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  3. Some information deleted
    Without aggregation being supported in both machines, it won't work.
    Etherent has a problem with looping when there are active loops in the
    physical topology, that is where Transparent Spanning Tree Protocol (STP) comes
    into play. In aggreagation the two links are treated as one so they have
    one mac filter table with load sharing usually based on simle XoR on the
    least significant bits of the source and destination Mac addresses. With
    out aggregation, STP would see the loop (If enabled) and place one of the
    links in standby. If you weren't running STP the first broadcast frame
    would start looping and us all available Bandwidth till you shutdown an

    I have been using the bridging tools on Linux for a while but havent
    tried aggreagation of links... but the other device needs to support this
    as well for the topology you desire.

    Jay R. Hickman
    Jay R. Hickman, Nov 10, 2003
  4. Chris Adams

    Dino Guest

    Dino, Nov 14, 2003
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