72 Part One • Theory
IP options from the main header. The options headers, if any, are simply
inserted into the datagram after the header and before the transport layer
protocol header. This way, routers can process datagrams without having
to process the options headers unless it is necessary—thus improving
performance overall for all datagrams.
RFC 1710 provides both a technical overview to the SIPP speciﬁcation and
a readable justiﬁcation and narrative of the protocol. It is worth a look, if
only to see how IPv6 as we know it came to be—because SIPP, with some
modiﬁcations, was the speciﬁcation recommended to and accepted by the
IESG as the basis for IPng.
4.5 IPv6, The Next Generation
RFC 1752, “The Recommendation for the IP Next Generation Protocol,”
published in January 1995, is a fascinating document that outlines clearly
what was needed and what was available, in terms of the candidate pro-
posals for successors to IPv4. In its summary, the authors of RFC 1752
describe what IPng would look like.
This protocol recommendation includes a simpliﬁed header with
a hierarchical address structure that permits rigorous route aggregation
and is also large enough to meet the needs of the Internet for the fore-
seeable future. The protocol also includes packet-level authentication
and encryption along with plug-and-play autoconﬁguration. The design
changes the way IP header options are encoded to increase the ﬂexibility
of introducing new options in the future while improving performance.
It also includes the ability to label trafﬁc ﬂows.
The ﬁfth item in a long list of speciﬁc recommendations is that IPng be
based on SIPP with 128-bit addresses. The rest of the RFC provides an
excellent resource for further historical background on how the Internet
research community identiﬁed and approached the problems associated
with IPv4, as well as detailed analysis of the three contenders, TUBA,
CATNIP, and SIPP. The RFC examines each proposal and discusses how
it meets (or fails to meet) the requirements and also presents the results of
the proposal review process.
All three proposals are praised in some way, and all ultimately con-
tributed something to the ﬁnal recommendation. For example, SIPP did