Broadcom NIC delays prevent DHCP during Kickstart

Michael_E_Brown at Michael_E_Brown at
Wed Oct 25 15:49:59 CDT 2006

If the driver takes the interface down at the physical level when it
loads, it will re-initialize the switches spanning-tree detection. I
know that the tg3 driver resets the interface at load time, which causes
this problem. I suspect that the intel driver does not take the
interface down at the physical level when it loads. This would mean that
the switch completes spanning tree detection on system power-on, and by
the time the driver loads it has completed.


	From: Kevin Kwast [mailto:kevintx at] 
	Sent: Wednesday, October 25, 2006 3:40 PM
	To: Brown, Michael E; linux-poweredge-Lists
	Subject: Re: Broadcom NIC delays prevent DHCP during Kickstart
	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 <Michael_E_Brown at
> 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.


			From: linux-poweredge-bounces at
[mailto:linux-poweredge-bounces at] 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> wrote: 

				> Is spanning tree enabled on the
				  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 :)

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