David Malone wrote:
> Does it talk about how jumbograms will apply to UDP? I suspect the
> max udp data size might be unchanged anyway...
It does (see below). And it does allow UDP packet with more than 64K of
data.
ftp://ftp.isi.edu/in-notes/rfc2675.txt
4. UDP Jumbograms
The 16-bit Length field of the UDP header limits the total length of
a UDP packet (that is, a UDP header plus data) to no greater than
65,535 octets. This document specifies the following modification of
UDP to relax that limit: UDP packets longer than 65,535 octets may be
sent by setting the UDP Length field to zero, and letting the
receiver derive the actual UDP packet length from the IPv6 payload
length. (Note that, prior to this modification, zero was not a legal
value for the UDP Length field, because the UDP packet length
includes the UDP header and therefore has a minimum value of 8.)
The specific requirements for sending a UDP jumbogram are as follows:
When sending a UDP packet, if and only if the length of the UDP
header plus UDP data is greater than 65,535, set the Length field
in the UDP header to zero.
The IPv6 packet carrying such a large UDP packet will necessarily
include a Jumbo Payload option in a Hop-by-Hop Options header; set
the Jumbo Payload Length field of that option to be the actual
length of the UDP header plus data, plus the length of all IPv6
extension headers present between the IPv6 header and the UDP
header.
For generating the UDP checksum, use the actual length of the UDP
header plus data, NOT zero, in the checksum pseudo-header [IPv6,
Section 8.1].
The specific requirements for receiving a UDP jumbogram are as
follows:
When receiving a UDP packet, if and only if the Length field in
the UDP header is zero, calculate the actual length of the UDP
header plus data from the IPv6 Jumbo Payload Length field minus
the length of all extension headers present between the IPv6
header and the UDP header.
In the unexpected case that the UDP Length field is zero but no
Jumbo Payload option is present (i.e., the IPv6 packet is not a
jumbogram), use the Payload Length field in the IPv6 header, in
place of the Jumbo Payload Length field, in the above calculation.
For verifying the received UDP checksum, use the calculated length
of the UDP header plus data, NOT zero, in the checksum pseudo-
header.
> The problem remains even if I punt on jumbograms though, how should
> I spell 65536?
The max. possible UDP data length is max. IP packet size - minimum IP
header length (w/o options) - UDP header length?
Lars
--
Lars Eggert <[EMAIL PROTECTED]> Information Sciences Institute
http://www.isi.edu/larse/ University of Southern California
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