Subject: [dhcwg] Query Regarding DHCP Lease time, Rebind Time and Renewal Time.

From: Ramesh Ganapathi <[email-masked]>
Date: Fri, 22 Oct 2010 11:50:57 +0530

Hi All,

Need clarification regarding the following:

1)     What should be the expected behavior if the DHCP client receiver a
OFFER with lease time of 0(zero).?

2)    If the DHCP Client receives DHCP OFFER with lease timer of 2 seconds
the T1(Rebind Timer) and T2 (Renew Timer) timer value will be round of to 1
second.

T1 = (lease time * 0.5) = 2*0.5 = 1

T2 = (lease time * 0.875) = 2 * 0.875 = 1.75 (round of to 1)

What should be expected behavior if the T1 and T2 timer value are same?

Thank you in Advance.

Warm Regards,

Ramesh.G

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From: Bud Millwood <[email-masked]>
Date: Fri, 22 Oct 2010 11:55:46 +0200

If the lease length is 0, then nothing about the offer is valid at all, IMO,
and it should be discarded.

- Bud

On Fri, Oct 22, 2010 at 8:20 AM, Ramesh Ganapathi <[email-masked]
> wrote:

> _______________________________________________
> dhcwg mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/dhcwg
>
>

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From: Ted Lemon <[email-masked]>
Date: Fri, 22 Oct 2010 11:00:59 -0400

On Oct 22, 2010, at 5:55 AM, Bud Millwood wrote:
> If the lease length is 0, then nothing about the offer is valid at all, IMO, and it should be discarded.

That's right.   If you try to process it, you will flood the network.

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From: Ramesh Ganapathi <[email-masked]>
Date: Sat, 23 Oct 2010 00:13:02 +0530

Hi Ted, Bud,
Thank you for the answers.

Regarding my query :
(2) If the DHCP Client receives DHCP OFFER with lease timer of 2 seconds the
T1(Rebind Timer) and T2 (Renew Timer) timer value will be round of to 1
second.

Can some one please clarify.

Thank you in advance.

--Ramesh.G

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From: Ramesh Ganapathi <[email-masked]>
Date: Sat, 23 Oct 2010 00:16:04 +0530

Regarding my query :

Thank you in advance.

--Ramesh.G

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From: Ted Lemon <[email-masked]>
Date: Fri, 22 Oct 2010 17:14:47 -0400

> Can some one please clarify.

You should expect that if you offer lease times that short, things will break, possibly in such a way as to take down your network with broadcast storms that will only stop when your DHCP server is shut down.   DHCP is not intended to offer leases that short.   As an example, I was recently staying at a motel where they offered two-minute leases.   *That* caused noticeable instability on my network because the VPN kept getting reset.   You really, really don't want to do this.

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From: "David W. Hankins" <[email-masked]>
Date: Tue, 26 Oct 2010 15:37:16 -0700

> OFFER with lease time of 0(zero).?

If it is a DHCPOFFER, the client hopefully would not select it in
SELECTING state, and would instead select a valid lease from a not
broken DHCPv4 server colocated on the network.

Realistically, DHCPv4 clients do not have very good selection
algorithms.

> What should be expected behavior if the T1 and T2 timer value are same?

This is a trick question.  In the case of a DHCPOFFER with a valid
lease time, the client continues to SELECTING state.

-- 
David W. Hankins	"If you don't do it right the first time,
Software Engineer		     you'll just have to do it again."
Internet Systems Consortium, Inc.		-- Jack T. Hankins

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From: "Bernie Volz (volz)" <[email-masked]>
Date: Sun, 31 Oct 2010 23:06:05 -0500

RFC 2131 states:

                                                       T1 MUST be
   earlier than T2, which, in turn, MUST be earlier than the time at
   which the client's lease will expire.

I didn't find any text such as in RFC 3315 about what the DHCPv4 client
should do if it receives T2 <= T1.

RFC 3315 states:

   If a client receives an IA_NA with T1 greater than T2, and both T1
   and T2 are greater than 0, the client discards the IA_NA option and
   processes the remainder of the message as though the server had not
   included the invalid IA_NA option.

So, I guess the DHCPv4 client could considers the OFFER (or ACK)
invalid. Another option would be to ignore the servers T1/T2 and just
use the default values?

- Bernie

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf
Of David W. Hankins
Sent: Tuesday, October 26, 2010 6:37 PM
To: DHC WG
Subject: Re: [dhcwg] Query Regarding DHCP Lease time, Rebind Time and
Renewal Time.

> the T1(Rebind Timer) and T2 (Renew Timer) timer value will be round of

> to 1 second.

This is a trick question.  In the case of a DHCPOFFER with a valid lease
time, the client continues to SELECTING state.