Date: Fri, 18 Aug 2006 15:27:35 +0300 From: Danny Braniss <danny@cs.huji.ac.il> To: "Martin Horcicka" <martin@horcicka.eu> Cc: pyunyh@gmail.com, freebsd-stable@freebsd.org, Dan Nelson <dnelson@allantgroup.com>, Alan Amesbury <amesbury@umn.edu> Subject: Re: FreeBSD boots too fast on Dell PE850 Message-ID: <E1GE3Rn-0004VF-TF@cs1.cs.huji.ac.il> In-Reply-To: Your message of Fri, 18 Aug 2006 14:00:06 %2B0200 .
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> 2006/8/18, Patrick M. Hausen <hausen@punkt.de>: > > > > On Fri, Aug 18, 2006 at 01:23:15PM +0200, Martin Horcicka wrote: > > > > > Unfortunately, I don't know how it works exactly. In our case when the > > > autodetection is disabled and there is e.g. 100/full configured > > > manually on both, switch and the FreeBSD box, ifconfig shows the > > > interface status wery early as "active". I suspect the switch (Cisco) > > > to activate the port (from the point of view of the FreeBSD box) but > > > not to forward any "normal" frames until the Spanning Tree Protocol > > > procedure is finished for that port. But it's just a guess. I don't > > > know the negotiation protocol in Ethernet at all and I would really > > > welcome a commentary from someone who does. > > > > This is indeed the case. > > > > The switch port goes up. Then the port goes into either the forwarding > > or the blocking state. The transition period usually takes between 30 > > and 50 seconds, which may be to long for some devices. > > > > spanning-tree portfast puts the port into the forwarding state > > immediately but still participates in STP, so eventually a loop > > will be detected and the port put back into blocking state again. > > This is a little off-topic (and I'm no Cisco specialist) but I'm > afraid that the loop detection won't happen with portfast. Cisco.com > says (the first page that Google gave me): > > --- > Understanding How PortFast Works > > Spanning-tree PortFast causes a port to enter the spanning-tree > forwarding state immediately, bypassing the listening and learning > states. You can use PortFast on switch ports connected to a single > workstation or server to allow those devices to connect to the network > immediately, rather than waiting for the port to transition from the > listening and learning states to the forwarding state. > > Caution: PortFast should be used only when connecting a single end > station to a switch port. If you enable PortFast on a port connected > to another networking device, such as a switch, you can create network > loops. > > When the switch powers up, or when a device is connected to a port, > the port normally enters the spanning-tree listening state. When the > forward delay timer expires, the port enters the learning state. When > the forward delay timer expires a second time, the port is > transitioned to the forwarding or blocking state. > > When you enable PortFast on a port, the port is immediately and > permanently transitioned to the spanning-tree forwarding state. > --- > > But then I don't see any difference between using portfast and > disabling Spanning Tree Protocol frames for that port at all. :-/ > because there isn't? if you are connecting a host to a switch, you can safely drop Spanning tree. from experience, even with SP enabled, the loop is detected, but not always the correct port is disabled :-(. danny > Martin > > > > The layer 2 interface is, of course, "up" during all this > > mumble - otherwise the switch could not send & receive STP frames. > > This is what confuses hosts waiting for DHCP or similar.
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