why we need 'bridge'

Discussion in 'Cisco' started by Mark, Sep 9, 2011.

  1. Mark

    Mark Guest


    many layer2 ethernet equipment vendor, Cisco as example, have a concept (I
    don't really know if it is correct to call it concept?) of a 'bridge', i.e.
    on cisco CLI one needs to explicitly create bridge:

    #conf t
    #(config) bridge 1 protocol ieee
    #interface fe0
    #bridge-group 1
    #interface fe1
    #bridge-group 1

    Why is it necessary ? As long as it is a switch, all the ports by default
    are in switchable, or this allows to have a number of independent bridges
    within one single physical device? Thanks in advance.

    Mark, Sep 9, 2011
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  2. This sounds suspiciously like homework already, so you only get a hint.

    Its unlikely that somebody setting up a cisco would bridge two ethers
    together, but they support other kinds..
    Doug McIntyre, Sep 9, 2011
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  3. Mark

    Mark Guest

    Thanks for reply. It's not a homework, although I'm student :) My guess
    after some research was that cisco originally supported multiple
    technologies (for ex. token ring, ethernet, fddi etc.), and it was naturally
    to allow a customer to bridge these ports in a single bridging entity.

    But I wasn't sure if my thoughts were right or wrong. Certainly I searched
    cisco.com, but they don't give much theeoretical background in this item

    Mark, Sep 9, 2011
  4. Indeed, WAN bridges was the primary use for bridge groups, not
    necessarily LAN to LAN bridging..
    Doug McIntyre, Sep 11, 2011
  5. Mark

    Stephen Guest

    there are even now some networks that need bridging and a router would
    not have all interfaces on the same switch module for hardware L2
    switching support - protocols like LAT have not died completely and
    bridging OSI CLNS was common at 1 point in carrier networks for
    managing SDH and similar kit

    This is usually on a router between Ethernet LANs and WAN interfaces.

    More recently Ethernet is taking over the high bandwidth WAN role, but
    even there routers get used on the LAN to WAN border to allow QoS +
    rate limiting etc in ways switches struggle with.

    A network i used to work on used bridging between the loopback and ATM
    PVCs for management traffic (i think - this is a while back)

    Stephen, Sep 14, 2011
  6. Mark

    Stephen Guest

    Put multiple switch modules such as the HWIC-4ESWs into a Cisco router
    and the ports within the module switch L2 locally, but the modules are
    not connected at layer 2......
    Still got lots of OSI CLNS running for SDH and other management = note
    carrier networks will be happily running kit well past the sell by
    Stephen, Sep 14, 2011
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