RFC 2147 (rfc2147) - Page 1 of 3
TCP and UDP over IPv6 Jumbograms
Alternative Format: Original Text Document
Network Working Group D. Borman
Request for Comments: 2147 Berkeley Software Design, Inc.
Updates: 1883 May 1997
Category: Standards Track
TCP and UDP over IPv6 Jumbograms
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
1. Overview
IPv6 supports datagrams larger than 65535 bytes long, often referred
to as jumbograms, through use of the Jumbo Payload hop-by-hop option
[Deering95]. The UDP protocol has a 16-bit length field that keeps
it from being able to make use of jumbograms, and though TCP does not
have a length field, both the MSS option and the Urgent field are
constrained by 16-bits. This document describes some simple changes
that can be made to allow TCP and UDP to make use of IPv6 jumbograms.
2. UDP Jumbograms
To allow UDP to make use of jumbograms, either the UDP length field
needs to be extended, or it needs to be ignored. Since the size of
the field can't be changed, a length of zero is used to indicate that
it is to be ignored, and the length in the "pseudo-header" is to be
used to determine the true length of the UDP header plus data. This
works because UDP length field includes the UDP header, so the
minimum valid value for this field is 8.
When sending a UDP packet, if and only if the length of the UDP
header plus data is greater than 65,535, set the length field in the
UDP header to zero.
Note 1: The length used in the "pseudo-header" for computing the
UDP checksum is always the true length of the UDP header plus
data, NOT zero [RFC-1883, Section 8.1].
Borman Standards Track
