[e2e] TCP Option Negotiation

Ralph Droms rdroms at cisco.com
Wed May 23 04:40:50 PDT 2001

In the usual case, DHCP clients will not use DHCPRELEASE so an assigned 
address will not be available for reassignment until the existing lease 
expires and the time remaining on a typical lease is much longer than the 
TCP quiet time.

However, I can point to a real-life scenario in which DHCPRELEASE is used 
and the quiet time might not be enforced.  I have DSL service at home - the 
DSL CPE is both a modem and a router.  The router is provisioned with a /30 
subnet, using one available address for the router while the other assigned 
through a DHCP server in the router.  To change computers on the DSL 
service, I do a DHCPRELEASE first so I don't have to wait for the lease to 
expire before the DHCP server will assign the available address to the new 
DHCP client.  If the new DHCP client is already running and polling for an 
address when the old client does its DHCPRELEASE, the server may reassign 
the address before the TCP quiet time expires.

I have experience with DHCPRELEASE being correctly implemented in both the 
Windows 98 and 2000 DHCP clients...

- Ralph

At 01:49 PM 5/17/2001 -0600, Vernon Schryver wrote:
> > From: Ralph Droms <rdroms at cisco.com>
> > I've had discussions about enforcing a quiet time in DHCP - a minimum 
> delay
> > time before reassigning an address to a new host.
> >
> > We've never heard a sufficiently strong argument to warrant adding the
> > requirement to the DHCP spec.
>Unless you assume the previous client does a DHCPRELEASE, won't
>there be an effective quite time of averaging half the lease period,
>and won't that be longer than the TCP MSL?
>Does any client do a DHCPRELEASE in real life?  I've tried to make some
>Windows boxes send DHCPRELEASE's in obvious situations (e.g. shutdown),
>but failed completely.
> >                                I don't know of any servers that 
> implement a
> > quiet time.
>For whatever it might be worth, please consider the recent question
>in either the main IETF mailing list or the DHCP WG mailing list
>from someone complaining about a "Assembly Line DHCP - Grace Period
>Problem" and pointing at what I understood to be
>http://support.microsoft.com/support/kb/articles/Q153/0/72.asp or
>4 or 24 hours plus the remaining lease time sounds like enough of a quiet
>time for most purposes.
>Vernon Schryver    vjs at rhyolite.com

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