Broadcom NIC delays prevent DHCP during Kickstart

Kevin Kwast kevintx at gmail.com
Wed Oct 25 15:39:57 CDT 2006


Any idea why the delay is long enough to prevent the DHCP packets with
Broadcom NICs but not Intel's?

Anyone know a kickstart option to increase the length of time it waits for
the NIC to initialize before sending the DHCP packets?

On 10/20/06, Michael_E_Brown at dell.com <Michael_E_Brown at dell.com> wrote:
>
>  When spanning tree is enabled, the switch port is always set to blocking
> mode when something is plugged in, that is, it will not pass traffic. It
> sets the port to blocking mode until after it has completed negotiation and
> figures out what is plugged into the other end of the cable. The time it
> takes for the switch to enable the port can easily reach 30 to 45 seconds
> when spanning tree is enabled. This is because the NIC in the computer
> doesnt understand the Hello packets that are being sent and ignores them,
> causing the switch to have to time out before it finally decides an end-host
> is plugged in and sets the port to forwarding mode.
>
> Some switches have an option similar to Cisco' portfast, which lets the
> switch go to forwarding mode much more quickly by changing the timeouts. We
> still recommend that ports connected to hosts have spanning tree disabled.
> --
> Michael
>
>  ------------------------------
> *From:* linux-poweredge-bounces at dell.com [mailto:
> linux-poweredge-bounces at dell.com] *On Behalf Of *Kevin Kwast
> *Sent:* Thursday, October 19, 2006 11:06 PM
> *To:* Mann, Andrew; linux-poweredge-Lists
> *Subject:* Re: Broadcom NIC delays prevent DHCP during Kickstart
>
> In my case, sure, spanning tree is on because every 5324 switch is
> interconnected with at least one other, and I haven't used the web interface
> to repeatedly set STP off for every port that is connected to a host.  Maybe
> the command line offers a way to turn off STP for 21 or 22 ports at a time
> on each switch?  I know that STP can cause delays after bringing up the
> ethernet link on a port, but Intel NICs don't seem to have this problem.  Is
> there a way to keep the ethernet link up between when the PXE boot uses it
> and the kickstarting Linux kernel tries to DHCP?  Or add 30 seconds to the
> amount of time it waits before it does the DHCP?  Thanks!
>
> On 10/19/06, Mann, Andrew <amann at ea.com> wrote:
> >
> >
> > > Is spanning tree enabled on the switch?
> >
> >   Is there a conflict with the Broadcom NICs and spanning tree?  We're
> > using a Cisco 4500 series switch with spanning tree enabled.  2550s,
> > 1750s, 1850s, and 1955 blades are able to quickly bring the NIC up and
> > start communicating.  2650s and 2950s have about a 30-60 second delay
> > between the time the NIC is enabled and communication succeeds.  After a
> > reboot, we have to run through and restart NTP on each of these types of
> >
> > system since this delay causes the ntp startup to fail.  It's only been
> > mildly annoying in the past, but getting rid of it would be nice :)
> >
> >
> > Andrew
> >
> >
>
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