In anycase, the killer problem i've had was people moving around laptops
that are already on (between vlans) and trying to get a new lease...or
people moving around their NIC to other ports at their desktop because they
are trying to troubleshoot some problem (ie porn too slow)..in either case
30 port initialization = helpdesk call (more than 30 seconds pass and
problem "fixes itself) = confused helpdesk = flustered user.
regards,
andrew
-----Original Message-----
From: Mikael Abrahamsson [mailto:swmike@swm.pp.se]
Sent: Saturday, July 07, 2001 2:58 AM
To: cisco-nsp@puck.nether.net
Subject: Re: portfast
On Sat, 7 Jul 2001, Ryan O'Connell wrote:
> On Sat, Jul 07, 2001 at 11:23:33AM +0200, Mikael Abrahamsson wrote:
> > I thought this was accounted for in the DHCP specs, that you need to
wait
> > at least 30 seconds before deciding that the dhcp server is unavailable.
A
> > lot of network cards do not do "link-up" until the driver initialises
the
> > card and thus you're in the 30 second wait period when you bring up the
> > link and then starts asking for dhcp servers.
>
> IIRC, Spanning Tree takes 30 seconds to go into forwarding state in the
absence
Yes, that is the default setting (probably in the RFC).
> Some Operating Systems (Windows NT 4 seems to be one, although I suspect
it was
> the fault of the driver, not the OS Kernel) actually start the DHCP
process
> before the network card has fully initialised, so you get less than 30
seconds.
> I've actually seen one extreme case (With 3Com 3C905s - both the B and the
C)
> where even the speed/duplex auto-negotiation phase is enough delay to
cause
> Windows to fail booting. It's an extreme case but it does happen. (DHCP
> eventually suceeded, but the PDC/BDC search phase had already timed out)
Then I believe those implementations are broken. Spanning tree has been
around forever and this forwarding delay should be known by all
and implementors should account for them.
I checked the DHCP/BOOTP RFCs but could find no values that
implementations are required to use when it comes to timeouts etc. I find
this odd. Making it a SHOULD or perhaps even a MUST to have at least 60
seconds timeout would probably be a good thing.
-- Mikael Abrahamsson email: swmike@swm.pp.se
This archive was generated by hypermail 2b29 : Sun Aug 04 2002 - 04:12:44 EDT