Subject: Re: DHCP Lease Time Option conclusion

From: Ted Lemon <[email-masked]>
Date: Fri, 17 Dec 1999 22:27:30 -0500 (EST)

> (a) Any DHCPDISCOVER or DHCPREQUEST without a lease time option is 
> treated as if it contained a request for the server's default lease. In 
> other words, *all* DHCPDISCOVER and DHCPREQUEST packets cause the 
> creation or sensible renewal of a lease. The server *never* simply offers 
> the dregs of a previous lease. If the server is configured to offer 
> 24-hour leases, then *all* DISCOVERS and REQUESTS that don't explicitly 
> request something different get a lease that lasts for 24-hours beginning 
> now.

I think this is actually correct - I have no idea what use it serves
to be able to ask how much time the server thinks is left on the
lease.   I'd be curious to know if any clients support this and/or
make use of it.

> (b) All normal DHCPDISCOVER or DHCPREQUEST packets that are not 
> "informational queries" MUST include a lease request option. If the 
> client has no particular care what the lease time should be, then the 
> client needs a way to communicate that. We can specify that a very large 
> lease request should be capped to the server's configured maximum, or 
> that a request for a lease of zero means a request for the default lease, 
> or that a request for a lease of 0xFFFFFFFE (one less than 'infinity') 
> means a request for the default lease.

Actually, I think the Solaris install floppy DHCP client requests an
infinite lease.   I know about this because when it first started
making the rounds, the ISC server started responding with bogus lease
times because I'd done the time arithmetic without accounting for the
possibility of overflow when adding a relative time to an absolute
time.   Needless to say, the ISC server is now more careful about
doing math on lease durations... :')

> Any comments?

Again, thanks for writing your experience up.   I'd like to see this
folded into RFC2131ng somehow!

			       _MelloN_

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From: Kim Kinnear <[email-masked]>
Date: Tue, 21 Dec 1999 10:51:53 -0500

Stuart,

You bring up some interesting questions.

My comments are inline, related to Ted's reply, below.

>lease.   I'd be curious to know if any clients support this and/or

I agree with Ted.  I too think this is correct.  I am somewhat
embarrassed to note that the paragraph where you don't get an
extension in a DISCOVER unless you asked for the specific IP
address was a surprise to me.  Seems a very strange overloading.

That said, I would object to revised language in the RFC that
said a server MUST offer an entirely new lease period to any
DHCPDISCOVER for several reasons -- I think the language should
be SHOULD, not MUST.

(The reasons are: 1) If two DHCPDISCOVERs come pretty close
together and the lease has almost all of its term still to go
before it expires, we'll offer the remaining lease time as
something of an optimization, and 2) failover causes all lease
time offers to be subject to failover correctness constraints.)

> > means a request for the default lease.

I think this is the wrong approach.  If the client doesn't care,
I think it should not include a lease time option.  I do like the
specification of how to ask for the max and min values, though.

Cheers -- Kim