Subject: RE: Turning off link-locals?

From: "Christian Huitema" <[email-masked]>
Date: Tue, 21 Jan 2003 22:25:08 -0800

>>Determining if DHCP is present may take a while.  For example, IP
>>address autoconfiguration in Windows takes a few minutes to give up on
>>DHCP and assign a LL address, which makes adhoc networking pretty
>>unusable.  The timeout could be configurable, but anything longer than a
>>few seconds is a hassle.  Is there a way to make this usable without
>>immediately acquiring a LL address when a new interface is brought up?
>
>Windows (at least recent versions) appears to always assign a LL address
>when an interface is brought up. If/when DHCP completes, the address is
>replaced with the assigned address. The degree to which that address is
>actually used by Windows while waiting for DHCP is unclear.

Not really. Adam MacBeth is correct: Windows (including the recent versions) will first try to get a DHCP address for about 1 minute, and will only resign itself to use an autonet address after that. However, the Windows stack will keep looking for a DHCP server after that, trying to contact DHCP every few minutes. This is probably the behavior that Daniel observed, i.e. a Windows system that is using an autonet address, presumably after waiting 60 seconds to configure it, but that continues hunting for a DHCP server.
 
-- Christian Huitema

---

From: Robert Elz <[email-masked]>
Date: Wed, 22 Jan 2003 16:45:00 +0700

Date:        Tue, 21 Jan 2003 22:25:08 -0800
    From:        "Christian Huitema" <[email-masked]>
    Message-ID:  <[email-masked]>

  | Not really. Adam MacBeth is correct: Windows (including the recent
  | versions) will first try to get a DHCP address for about 1 minute,

And one assumes, that should there be lots of complaints about the time
that is taking (compared to other things happening in parallel that
people are waiting for anyway - virus scanners and such), then the
amount of effort it would take to lower that minute to 10 seconds, or
something, would not bankrupt Microsoft?    (Ignoring distribution,
those who want the mod can just fetch a patch).

In the vast majority of cases, if you haven't received signs of DHCP
server activity in a couple of seconds, you're not going to get any by
waiting longer, or sending more requests.   (Of course, once you have
some evidence that a DHCP server is out there and responding, then you
can take longer to complete the process in the unlikely case it is necessary).

I guess that the reason for "1 minute" though, is so that a DHCP server
can still be found if the system is connected to a switch that is going
to run the spanning tree protocol (for 45 seconds) after the system
initializes its LAN interface.   If that's what it is about, then it is
even more crucial that any LL address acquisition attempts also continue
for about a minute (after LAN initialization) for the same reason - the
node cannot possibly get back an "address in use" notification during the
spanning tree interval.

This suggests a minimum automatic configuration interval that can't
really be reduced, no matter how much some people would like to have it
complete as fast as possible.

In fact, the draft should probably say that an LL address cannot be acquired
within a minute of LAN initialization, precisely to avoid this problem.

kre