Broadcom NIC delays prevent DHCP during Kickstart

[Michael_E_Brown at Dell.com]

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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