RE: [dhcwg] DHCPv4

yet another argument for revising the draft...  wonder if Rob and I can make
the deadline for the Paris IETF meeting (not that *I* can attend, darn it!)

--Barr

> -----Original Message-----
> From: dhcwg-bounces@ietf.org [mailto:dhcwg-bounces@ietf.org]On Behalf Of
> Simon Kelley
> Sent: Saturday, May 07, 2005 08:55
> To: Bernie Volz (volz)
> Cc: dhcwg@ietf.org
> Subject: Re: [dhcwg] DHCPv4 - definition of maximum message size.
>
>
> Bernie Volz (volz) wrote:
> > It is too bad Barr Hibb's "RFC 2131 Implementation Issues" draft has
> > expired. See text below. The key part is:
>
> That's a valuable document which I'd not come across before, thanks.
>
> In case is ever gets revived, I have an addition to section 2.21,
> "Option Ordering"
>
>  >A number of clients exist that require that the DHCP message type be
>  >the first option (after the magic cookie).  We SHOULD restate that
>  >the client MUST NOT make any such assumption.  The only known
>  >ordering constraint concerns option 82, which is last.  CMTS vendors
>  >want it to be last, but suppose someone else wants their pet option
>  >to be last also -- how would we resolve this conflict?
>
> There's at least on widely deployed client (The Intel PXE client) which
> depends on option 60 (vendor class identifier) preceeding option 43
> (Vendor specific information.) So that's another constraint to add to
> the list.
>
>
>
> >         o  Clients SHOULD communicate their link-layer frame size to the
> >
> >            DHCP server via the DHCP MTU option.
> >
> > So, this is *LINK-LAYER* frame size.
> >
> > I believe this 576 size comes from RFC 791:
> >
> >   Total Length:  16 bits
> >
> >     Total Length is the length of the datagram, measured in octets,
> >     including internet header and data.  This field allows the length of
> >     a datagram to be up to 65,535 octets.  Such long datagrams are
> >     impractical for most hosts and networks.  All hosts must be prepared
> >     to accept datagrams of up to 576 octets (whether they arrive whole
> >     or in fragments).  It is recommended that hosts only send datagrams
> >     larger than 576 octets if they have assurance that the destination
> >     is prepared to accept the larger datagrams.
> >
> >     The number 576 is selected to allow a reasonable sized data block to
> >     be transmitted in addition to the required header information.  For
> >     example, this size allows a data block of 512 octets plus 64 header
> >     octets to fit in a datagram.  The maximal internet header is 60
> >     octets, and a typical internet header is 20 octets, allowing a
> >     margin for headers of higher level protocols.
> >
> > So, it should be treated as the "IP + UDP + DHCP" packet size.
> >
>
> That's clear, I'll log a bug report against the client which sends a
> Max. message of 548.
>
> Cheers,
>
> Simon.
>
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RE: [dhcwg] DHCPv4 - definition of maximum message size.