Autonegotiation, DTP, PAgP, and STP steps a port moves through

Discussion in 'Cisco' started by John Sasso, Aug 13, 2004.

  1. John Sasso

    John Sasso Guest

    I finished reading a paper from Cisco, "Monitoring PIX Performance," and
    p.2-3 describes the impact that autonegotiation, portfast, etherchanneling
    (PAgP), and dynamic trunking protocol (DTP) have on a port or interface
    coming up to the point where it can starting passing traffic normally.

    My question is: assuming an end device (e.g., PIX) is connected to a
    Catalyst switch port that itself has channeling set to auto, trunking set to
    auto, portfast disabled, and speed/duplex set to auto, what are the phases
    the switch port goes through before finally getting to the state where it
    starts passing data traffic normally. For example, is it:

    Speed/Duplex Negotiated -> Channeling negotiated -> Trunking
    negotiated -> Spanning Tree phases -> Port starts processing data traffic

    Cisco's paper is interesting, in that it notes that PAgP frames can be
    impacted by speed/duplex negotiation, and incur a delay of 3 sec prior to
    port forwarding traffic. If portfast is disabled, then there's a delay of
    30 sec. If DTP is enabled, then a delay of 15 sec is incurred. Thus, I
    ponder if the total delay (from the point a device is powered on or
    connected to the switch port) would be 3 + 30 + 15 = 48 sec before the
    device can start effectively passing data traffic with the switch.

    So, 2 questions here. Any insight would be greatly appreciated!

    John Sasso, Aug 13, 2004
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  2. John Sasso

    joe Guest

    Any router or pix should be a "host port" to a switch...

    this means all switch to switch protocols disabled... a layer 3 device
    or workstation should have no use for these protocols..

    set port host
    joe, Aug 14, 2004
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  3. John Sasso

    John Sasso Guest

    That does not answer my question. Yes, I've understood long ago about
    disabling DTP, PAgP, and enabling portfast on such ports.

    My question is what steps does a port go through before finally passing
    data traffic normally, assuming the port had DTP and channeling set to
    auto, no portfast, and had speed/duplex set to auto. For example, would
    it first do Speed/Duplex Negotiation, followed by Channeling
    negotiation, followed by Trunking negotiation, followed by Spanning Tree
    phases? Thats all.


    John Sasso, Aug 14, 2004
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