mar@ATHENA.MIT.EDU (02/17/88)
Recent discussion about mail problems indicates that some people have been having problems coordinating host configuration changes. Here are some hints from an address change I performed a while back. The goal was to change the address on every host in our installation, including 2 listed in the hosttable, our domain nameserver, and our mail hub. We planned this a couple of months in advance. The steps we followed were: 1. Turn on both sets of addresses in our gateways, and use a PC configured on the new network address to make sure we had connectivity with the rest of the internet. 2. Notified the NIC that we were planning the change for about a month later, and got back confirmation that they could change the hosttables on the day we chose. Also notified the system administrator at the machine serving as secondary nameserver for our domain, and got confirmation that they would be able to make the change on the correct day. 3. Changed the timeouts in our name domain to 1 hour so that resolvers wouldn't cache our old address for 3 days after the change. 4. A couple of days before the change we changed the sendmail.cf on our mailhub to put: Notice: foo.arpa's address will be 1.2.3.4 after April 1 lines in the headers of all mail passing through. 5. We also started changing the addresses of PC's and lesser known workstations a day early, just because it would take too long to change everything at once. 6. On the flag day, we first checked with the NIC to see that they had the new information. We would have called off the change if they hadn't done it yet. We then changed the addresses of our well known machines, and swapped in the new domain database. We changed the text of the extra header line in the message slightly. Since our secondary nameserver is run by a different organization at a different site, as suggested in the RFC, hosts that had cached the old information could still get to us. They would be unable to contact our primarhy nameserver at the old address, so try the secondary nameserver (which hadn't moved) and get our new addresses from there. 7. I then monitored our gateway log for the next week to catch hosts attempting to contact our old address. When I spotted these, I sent mail to the postmaster at those sites informing them of our move and that they should get new hosttables. The whole thing was relatively painless, with not much disruption of service. The flag day was on a Friday, so that caches would have a better chance of timing out by Monday when people wanted to do work again. The key to the operation was planning it a couple of months in advance, and not going from one stage to the next until we were sure it was going to work. If you are forced to make a change like this on short notice, I imagine that there would be many more problems. -Mark