Help needed about Implementation of "Spanning Tree Protocol" for switch

Discussion in 'Cisco' started by GS, Sep 17, 2005.

  1. GS

    GS Guest

    A switch contains 3 uplinks which are on WAN side and there 30 LAN
    ports for subscriber side, how to implement Spanning tree protocol
    (802.1d) in this switch?. Can somebody suggest how to implement STP and
    what are the things has to take care on interface level?. Thanks in
    advance. We have chip called "xyz" which inter connects WAN and LAN.
    Thanks in advance.
     
    GS, Sep 17, 2005
    #1
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  2. In article <>,
    GS <> wrote:
    :A switch contains 3 uplinks which are on WAN side and there 30 LAN
    :ports for subscriber side, how to implement Spanning tree protocol
    :(802.1d) in this switch?. Can somebody suggest how to implement STP and
    :what are the things has to take care on interface level?. Thanks in
    :advance. We have chip called "xyz" which inter connects WAN and LAN.

    Sorry, GS, your question looks suspiciously like a course assignment.

    If you are actually working for a company that designs switches,
    then I would expect you to have read the appropriate RFCs throroughly
    and to ask -specific- questions -- and I would expect that the
    company would have hired someone who had switch design experience.

    --
    'The short version of what Walter said is "You have asked a question
    which has no useful answer, please reconsider the nature of the
    problem you wish to solve".' -- Tony Mantler
     
    Walter Roberson, Sep 17, 2005
    #2
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  3. GS

    GS Guest

    Actually I am looking for some info about how spanning tree protocol
    can be interfaced with WAN and LAN ports?, that's all I needed.
     
    GS, Sep 18, 2005
    #3
  4. In article <>,
    GS <> wrote:
    :Actually I am looking for some info about how spanning tree protocol
    :can be interfaced with WAN and LAN ports?, that's all I needed.

    The Spanning Tree Protocol doesn't care whether a port is a WAN
    or LAN port. You can send BPDU on a WAN link.

    Whether it is worth sending BPDUs or not depends upon whether there is
    any possibility that the far hop of the WAN link might have topology
    loops that you need to arbitrate between.


    Perhaps you are asking about a different matter, which is to say
    tunneling of BPDUs over WAN links, so that you can have an
    extended "layer 2" path resolution instead of using a "routing"
    path resolution? If that's what you are trying to do, then this
    article might be of interest:

    http://www.netcraftsmen.net/welcher/papers/metroeth01.html
    --
    Feep if you love VT-52's.
     
    Walter Roberson, Sep 18, 2005
    #4
  5. GS

    GS Guest

    This whole STP/Bridge implementtaion does really care about hardware
    interfaces (physical ports)? Or is it everything is in software only,
    for example, if the port's state is changed (if the port is got
    disconnected)?. Thanks.
     
    GS, Sep 20, 2005
    #5
  6. In article <>,
    GS <> wrote:
    :This whole STP/Bridge implementtaion does really care about hardware
    :interfaces (physical ports)? Or is it everything is in software only,
    :for example, if the port's state is changed (if the port is got
    :disconnected)?. Thanks.

    I'm still not sure what you are trying to do.

    STP is a layer 2 protocol, not a routed protocol. If you have a WAN
    port which is transmitting BPDU's to you, then the STP information
    so carried will be taken into account in the construction of the tree.

    If you had a situation where you had multiple WAN connections that were
    linked together at layer 2 on the remote end and so were determined by
    STP to be part of the same tree, then because WAN links are often much
    slower than LAN links, those WAN links would tend to be deemed to have
    a high cost, you could end up with all the WAN traffic directed to
    the WAN link that happened to have the lowest MAC address (or based
    on one of the other STP resolution criteria.)

    It would, however, be quite unusual for multiple WAN links to be
    joined together remotely in a common tree -- rare enough that
    *probably* it would only occur if you were deliberately bridging BPDU
    from a remote site to implement an extended LAN.

    If the WAN links sent you BPDU at all (which is not particularily
    likely) then they would very likely appear to be distinct leafs, to
    be detected by STP as not having any topology loops. There might be
    a layer 3 topology loop involved, but STP is not designed to detect
    layer 3 topology loops.

    If the STP has determined that a particular WAN link is a leaf,
    then when that WAN connection goes down, if you are using classic
    STP then the spanning tree will be recalculated -- and will be
    determined to be exactly the same as it was before. If you are
    are using RSTP (Rapid Spanning Tree Protocol) then in the same
    circumstances, the switches would have figured out that that WAN
    link was not a potential backup link, and so would know that the
    topology would not change, and would supress notification of the
    event to the other switches.
    --
    Goedel's Mail Filter Incompleteness Theorem:
    In any sufficiently expressive language, with any fixed set of
    email filtering algorithms, there exists at least one spam message
    which the algorithms are unable to filter out.
     
    Walter Roberson, Sep 20, 2005
    #6
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