Monday, July 21, 2014

Happy (early) 20th anniversary, IPv6

My first full-time job out of school was with the The U.S. Naval Research Laboratory. It was a spectacular opportunity. I was going to be working on next-generation (at the time) Internet Protocol research and development.

When I joined in early 1994, the IPng proposals had been narrowed to three:

  • SIPP - Simple Internet Protocol Plus. 8-byte addresses, combined with a routing header that could, in theory, extend the space even further (inherited from IPng contender PIP).
  • TUBA - TCP Using Big Addresses. The use of OSI's CLNP with proven IPv4 transports TCP and UDP running over it.
  • CATNIP - Common Architecture for the Internet. I never understood this proposal, to be honest, but I believe it was an attempt to merge CLNP and IPv4.

NRL, well, my part of NRL, anyway placed its bet on SIPP. I was hired to help build SIPP for then-nascent 4.4BSD. (The first 10 months were actually on 4.3 Net/2 as shipped by BSDI!) It was a great team to work with, and our 1995 USENIX paper displayed our good work.

Ooops... I'm getting a bit ahead of myself.

The announcement of the IPng winner was to be at the 30th IETF meeting in Toronto, late in July. Some of us were fortunate to find out early that what would become IPv6 was SIPP, but with 16-byte addresses. Since I was building this thing, I figured it was time to get to work before Toronto.

20 years ago today, I sent this (with slightly reordered header fields) mail out to a subset of people. I didn't use the public mailing list, because I couldn't disclose SIPP-16 (which became IPv6) before the Toronto meeting. I also discovered some issues that later implementors would discover, as you can see.

From: "Daniel L. McDonald" <danmcd>
Subject: SIPP-16 stuff
To: danmcd (Daniel L. McDonald), cmetz (Craig Metz), atkinson (Ran Atkinson),,,,,,,,,,, nordmark@jurassic-248.Eng.Sun.COM,,
Date: Thu, 21 Jul 1994 19:20:33 -0500 (EST)
X-Mailer: ELM [version 2.4 PL23]
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Message-ID:  <>
Content-Length:  1578
Status: RO
X-Keywords: NotJunk         
X-UID: 155

SIPP folks,

Has anyone tried quick-n-dirty SIPP-16 mods yet?

We have managed to send/receive SIPP-16 pings across both Ethernet and
loopback.  UDP was working with SIPP-8, and we're working on it for SIPP-16.
Minor multicast cases were working for SIPP-8 also, and will be moved to
SIPP-16.  TCP will be forthcoming once we're comfortable with some of the
protocol control block changes.

My idea for the SIPP-16 sockaddr_sipp and sipp_addr is something like:

 struct sipp_addr {
  u_long words[4];

 struct sockaddr_sipp {
  u_char ss_len;     /* For BSD routing tree code. */
  u_char ss_family;
  u_short ss_port;
  u_long ss_reserved;
  struct sipp_addr ss_addr;

We've managed to use the above to configure our interfaces, and send raw
SIPP-16 ICMP pings.  I've a feeling the routing tree will get hairy with the
new sockaddr_sipp.  The size discrepancy between the sockaddr_sipp, and the
conventional sockaddr will cause other compatibility issues to arise.
(E.g. SIOCAIFADDR will not work with SIPP, but SIOCAIFADDR_SIPP will.)

We look forward to the implementors meeting, so we can talk about bloody
gory details, experience with certain internals (PCBs!), and to find out
how far behind we still are.

Dan McD, Craig Metz, & Ran Atkinson
Dan McDonald       | Mail:  {danmcd,mcdonald} --------------+
Computer Scientist | WWW:   |
Naval Research Lab | Phone: (202) 404-7122        #include <disclaimer.h>    |
Washington, DC     | "Rise from the ashes, A blaze of everyday glory" - Rush +

Funny how many defunct-or-at-least-renamed organizations are in that mail (Sun, DEC, Bellcore) are in that mail. BTW, for Solarish systems, the SIOCSLIFADDR (note the 'L') became the ioctl of choice for longer sockaddrs. Also, this was before I discovered uintN_t data types.

If it wasn't clear from the text of the mail, we actually transmitted IPv6 packets across an Ethernet that day. It's possible these were the first IPv6 packets ever sent on a wire. (Other early implementations used IPv6-in-IPv4 exclusively.) I won't fully claim that honor here, but I do believe it could be true.


  1. I'll post a counter claim and say that the DEC Unix implementation could well have sent packets at or before that date :) Did I reply to your email ?

    Peter (was


      It's possible you did. Yes, yes you did. It wasn't clear if you sent 'em over a wire, though. (My future co-workers at Sun did over-IPv4 at first, e.g.)

      I'll forward you the response you sent me.