Subject: [dhcwg] Option length question(s)

From: "James M. Polk" <[email-masked]>
Date: Tue, 30 Aug 2005 18:07:51 -0500

Hey

The maximum length of a DHCP message is 576 bytes, but no single option can 
be longer than 255 bytes. I understand that this all can be negotiated 
between the client and the server to other lengths - but I'm having a bit 
of difficulty finding the RFC(s) that say this, while providing the 
specific rules around how this can occur.

Can someone help with this pointer?

Thanks

cheers,
James

                                 *******************
                 Truth is not to be argued... it is to be presented.

_______________________________________________
dhcwg mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/dhcwg

---

From: Andre Kostur <[email-masked]>
Date: Tue, 30 Aug 2005 16:22:10 -0700

James M. Polk wrote:

> Hey
>
> The maximum length of a DHCP message is 576 bytes, but no single 
> option can be longer than 255 bytes. I understand that this all can be 
> negotiated between the client and the server to other lengths - but 
> I'm having a bit of difficulty finding the RFC(s) that say this, while 
> providing the specific rules around how this can occur.
>
The maximum length of a DHCP message is undefined (but I presume must 
fit within a single UDP message).

However, clients are required to accept messages up to 576 bytes.  The 
client may tell the server that it can accept larger.

RFC 2131, section 2, page 10, last paragraph.

An option may be of nearly arbitrary length (although still has to fit 
in the DHCP message...).  RFC 2131, section 4.1, page 24, 2nd 
paragraph.  Futher clarified in RFC 3396.

A single _instance_ of an option may be no longer than 255 bytes.  This 
is a consequence of the 1-byte length for an option.