Subject: [dhcwg] Query on DHCPINFORM message

From: Muneer <[email-masked]>
Date: Mon, 5 Dec 2005 11:09:29 +0530

Hi,

   I need a clarification on DHCP inform message. Is it applicable
only to manually configured hosts? Can I use it in the following
scenario?

I have a host which got IP address through DHCP. Its renewal is after
10 days. On the first day I added some more options in the server. Can
I send an Inform message from the client to get these updated options?
Is it a violation to the standards?

--
Imagination is more important than knowledge...

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From: Andre Kostur <[email-masked]>
Date: Mon, 05 Dec 2005 02:40:03 -0800

> only to manually configured hosts? Can I use it in the following

No, I've seen it used on dynamic hosts.

> I send an Inform message from the client to get these updated options?

No.  DHCPINFORM is a client->server message.  You want DHCPFORCERENEW 
(althought I don't know anybody who implements it yet).

> Is it a violation to the standard?

Yes.  You want the message to go the wrong way.

---

From: Muneer <[email-masked]>
Date: Mon, 5 Dec 2005 17:13:10 +0530

> No, I've seen it used on dynamic hosts.

Can you give an example situation where client needs to send inform
message? Dynamic host will aquire IP through dhcp. This mesage
sequence itself is used to get the remaining parameters also. So where
does it need to send the INFORM message separately?

> Yes.  You want the message to go the wrong way.

I think you have mistaken my question. Administrator configures the
new parameter in the server. He wants the client to be updated. So he
goes to the client and forces the client to send an INFORM message to
the server. Is this legal? Or is he suppose to send a renew message
(like force renew)?

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From: Andre Kostur <[email-masked]>
Date: Mon, 05 Dec 2005 03:52:17 -0800

> does it need to send the INFORM message separately?

As I recall, some version of the Novell Netware client on Windows needed 
some of the options that were being returned by the DHCP sever, but the 
Netware client couldn't (or wouldn't) access the original response.  So 
after the device obtained an address, the Netware client would emit the 
DHCPINFORM to solicit a response to itself so it could read the 
appropriate options.
> the server. Is this legal? Or is he suppose to send a renew message
Whups... I did misread.  Somehow I read that you wanted to send the 
Inform _to_ the client.  My mistake. 

Yes, you could send an inform from the client to the server to get the 
new options.  A renew would probably accomplish the same thing (and is 
guaranteed to already be implemented on the client...).  I think most 
people would just have the client renew.

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From: "David W. Hankins" <[email-masked]>
Date: Mon, 5 Dec 2005 08:16:20 -0800

> does it need to send the INFORM message separately?

It may not in fact be the operating system at all.

Some http clients look for DHCP options the host operating system doesn't
know to put in its requested options list.

So, these user-space applications send their own INFORM once they've
been loaded by the user.

The advantage being that they can do so to acheive DHCP configuration
options without interfering with the lease expiration time.

Of course it would be nice if the host operating system learned to ask,
since there is no timer for refreshing information discovered via INFORM.

-- 
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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