Spanning-Tree

Discussion in 'Cisco' started by Raimond Alpers, Dec 25, 2003.

  1. Hello!
    Does anybody know, which trunk-methods allow a spanning-tree instance per
    VLAN???

    a.) ISL
    b.)802.1q
    c.)both

    c.) is correct. From my point of view a.) is correct, because 802.1q support
    a spanning-tree instance for all VLANs. (There are different descriptionn in
    e-books).

    Thanks for comments

    Ray
     
    Raimond Alpers, Dec 25, 2003
    #1
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  2. In article <bseq69$enp$00$-online.com>,
    Raimond Alpers <> wrote:
    :Does anybody know, which trunk-methods allow a spanning-tree instance per
    :VLAN???

    :a.) ISL
    :b.)802.1q
    :c.)both

    :c.) is correct. From my point of view a.) is correct, because 802.1q support
    :a spanning-tree instance for all VLANs.

    Cisco impliments a common extension to 802.1Q that allows per-VLAN
    spanning trees.
    --
    Are we *there* yet??
     
    Walter Roberson, Dec 25, 2003
    #2
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  3. Raimond Alpers

    shope Guest

    "Walter Roberson" <-cnrc.gc.ca> wrote in message
    news:bsf1gk$ptp$...
    > In article <bseq69$enp$00$-online.com>,
    > Raimond Alpers <> wrote:
    > :Does anybody know, which trunk-methods allow a spanning-tree instance per
    > :VLAN???
    >
    > :a.) ISL
    > :b.)802.1q
    > :c.)both
    >
    > :c.) is correct. From my point of view a.) is correct, because 802.1q

    support
    > :a spanning-tree instance for all VLANs.
    >
    > Cisco impliments a common extension to 802.1Q that allows per-VLAN
    > spanning trees.


    but the OP is right - that isnt in the 802.1Q definition - its an extension.

    BTW - this sounds like a multi choice test Q - any one heard of this kind of
    creative approach to certification that is so common being challenged? After
    all, if the test doesnt use correct factual info, and company discounts for
    resellers etc depend on the results (in my employers case this could run
    into 7 digit numbers of $), there has to be a law suit in there at some
    point......

    Note that the cisco version of 802.1Q is compatible with some other varients
    of multiple spanning tree on 802.1Q, but i dont know of any comprehensive
    compatibility testing. And i have stumbled across some wierd interaction
    issues.

    BTW - there is another flavor now we have 802.1s / 802.1w spanning tree
    extensions - which work differently to the 802.1Q extensions. Not an issue
    if you stick to 1 manufacturer, but that never seems to be survive contact
    with network changes and upgrades.

    i have to admit that i usually try to design out spanning tree as i have had
    so many problems with marginal stuff with this - CPU load, 1 way link loops,
    unstable parameters, new root disrupting topology and so on. And the less
    said about VTP the better.
    > --
    > Are we *there* yet??

    --
    Regards

    Stephen Hope - remove xx from email to reply
     
    shope, Dec 25, 2003
    #3
  4. Raimond Alpers

    Steinar Haug Guest

    ["shope"]

    | i have to admit that i usually try to design out spanning tree as i have had
    | so many problems with marginal stuff with this - CPU load, 1 way link loops,
    | unstable parameters, new root disrupting topology and so on. And the less
    | said about VTP the better.

    Amen, especially on the VTP part. We turn off VTP on all our Cisco
    switches, after having had way too many problems with it.

    Steinar Haug, Nethelp consulting,
     
    Steinar Haug, Dec 25, 2003
    #4
  5. Raimond Alpers

    Ron Bandes Guest

    According to the IEEE 802.1Q 1998 standard in clause 6.7: "This standard
    defines a VLAN environment that operates over a single Spanning Tree."

    However, at
    http://www.cisco.com/en/US/tech/tk389/tk621/tk847/tech_protocol_home.html it
    says:
    "Per VLAN Spanning Tree Plus (PVST+) provides the same functionality as PVST
    using 802.1Q trunking technology rather than ISL. PVST+ is an enhancement to
    the 802.1Q specification and is not supported on non-Cisco devices."

    So it seems that the answer is that Cisco's implementation of 802.1Q, which
    exceeds the standard, supports Per VLAN Spanning Tree, but the IEEE standard
    does not.

    Ron Bandes
    CTT, CCNP, MCSE

    "Raimond Alpers" <> wrote in message
    news:bseq69$enp$00$-online.com...
    > Hello!
    > Does anybody know, which trunk-methods allow a spanning-tree instance per
    > VLAN???
    >
    > a.) ISL
    > b.)802.1q
    > c.)both
    >
    > c.) is correct. From my point of view a.) is correct, because 802.1q

    support
    > a spanning-tree instance for all VLANs. (There are different descriptionn

    in
    > e-books).
    >
    > Thanks for comments
    >
    > Ray
     
    Ron Bandes, Dec 25, 2003
    #5
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