It was sort of a soft change over. All the did on January 1, 1983, is disable link 0 on the IMPs. This essentially blocked NCP from working anymore. You could (and many of us were) run IP on the Arpanet for years before that. In fact the weeks before we were getting ready for the change and we had our TCP/IP version of the system up. It crashed. We rebooted it and set about debugging it. It crashed again. Immediately my phone rang. It was Louis Mamakos, then of the University of Maryland. He had tried to ping our system. I called out the information to Mike Muuss who was across the desk from me. We set to find the bug. It turned out that the ICMP echo handling in the 4.1c (I believe this was the version) that we'd cribbed our PDP-11/70 TCP from had a bug where it used the incoming message to make the outgoing one, AND it freed it, eventually causing a double free and crash. It was at this point we realized that BSD didn't have a ping client program. Mike set out to write one. It oddly became the one piece of software he was most known for over the years. The previous changeover was to long leaders on the Arpanet (Jan 1, 1981?). This changed the IMP addressing space from eight bits (6 bits for imp number, 2 for a host on imp) to 16 bits for imp number and 8 for a host on imp. While long leaders were available on a port basis for years earlier, they didn't force the change until this date. The one casualty we had a PDP-11/40 playing terminal server running software out of the University of Illinois called "ANTS." Amusingly the normal DEC purple and red logo panels at the top of the rack were silkscreened with orange ANTS logos (with little ants crawling on it). The ANTS wasn't maintained anymore and stuck in short-leader mode. We used that option to replace that machine with a UNIX (we grabbed one of our ubiquitous PDP-11/34's that were kicking around). I kept the racks and the ANTS logo for the BRL Gateways. I turned in the non-MM PDP-11/40. A year later I get a call from the military supply people. ME: Yes? GUY: I need you to identify $65,000 of computer equipment you turned in. ME: What $65,000 machine? GUY: One PDP-11/40 and accessories. ME: That computer is 12 years old... and I kept all the racks and peripherals. Do you know how much a 12-year-old computer is worth? The other major cut over was in October of 1984. This was the Arpanet-Milnet split. I had begged the powers that be NOT to do the change over on the Jan 1st as it always meant I had to be working the days leading up to it. (Oct 1 was the beginning of the "fiscal" year). Our site had problems. I made a quick call to Mike Brescia of BBN. This was pre-EGP, and things were primarily static routed in those days. He'd forgotten that we had routers at BRL now on the MILNET (all the others were on the ARPANET) and the ARPANET-MILNET "mail bridge" routers had been configured for gateways on the MILNET side.