Subject: [dhcwg] Maximum message size interpretation

From: Bud Millwood <[email-masked]>
Date: Fri, 15 Feb 2002 11:25:31 +0100

When a client gives my server the maximum message size it can receive, should 
I interpret that as the total IP packet size the client can receive or just 
the size of the DHCP portion?

From the description of this option, it appears that I should interpret the 
value as the size of the entire IP packet the client can receive.

In other words, should I subtract IP and UDP header sizes from a client's 
Maximum Message Size value?

- Bud

Bud Millwood
Weird Solutions, Inc.
http://www.weird-solutions.com
tel: +46 70 566 7803
fax: +46 8 758 3687
mailto:[email-masked]

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From: Tobin Coziahr <[email-masked]>
Date: Tue, 19 Feb 2002 01:22:08 -0800

Bud-

The Maximum Message Size option is also known as the "maximum DHCP
message size" option (See RFC 2131, page 9-10).  This ONLY refers to the
size of the DHCP packet itself, without the IP and UDP headers.  The
point of the option is to let servers use messages larger than 548
bytes, which is the default max.

So no, don't subtract the header size.

-Tobin 

-- 
Tobin Coziahr			650-786-7118 (x87118)
Solaris Networking		[email-masked]
Sun Microsystems

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From: Thomas Narten <[email-masked]>
Date: Tue, 19 Feb 2002 06:34:04 -0500

Hmm. That's not what draft-ietf-dhc-csr-06.txt says:

>    stack is capable of reassembling fragmented IP datagrams.  In this
>    case, the client SHOULD set the value of this option to at least
>    the MTU of the interface that the client is configuring.   The
>    client MAY set the value of this option higher, up to the size of
>    the largest UDP packet it is prepared to accept. (Note that the
>    value specified in the Maximum DHCP Message Size option is the
>    total maximum packet size, including IP and UDP headers.)

Is the above text correct?

Thomas

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From: Tobin Coziahr <[email-masked]>
Date: Tue, 19 Feb 2002 03:59:42 -0800

My apologies, you're right.  All of the information I just found on the
subject notes that the minimum value for this option is 576, which along
with the RFC that you quoted shows that I was mistaken.

The Maximum Message Size option DOES include the IP and UDP headers.

Thanks for the correction, Thomas.

-Tobin