Had some strange problems after the upgrade. A number of strange problems occured, most related to slow connections to mail or connections timing out, but there were other spurious problems as well. Looking at logs, I saw random name server failures, but testing our name servers (from eskimo) didn't reveal any problems. The mail machine itself showed no signs of ill-health. Finally (about 7am after being up all night), I re-arranged the name servers that mail uses so that ns1.eskimo.com (which is a virtual interface on eskimo presently) wasn't first, and then I could connect to it right away. I tried pinging ns1 from mail and couldn't. I did an arp -a and noticed the ethernet address was incorrect. Well, I've run into this problem before where SunOS wants to hang on to old arp entries after hardware is changed, and it's a real pain in a sizeable network because you can get it cleared from one machine but another machine with a bad entry will respond to an arp request with it's bad entry polluting the arp table of a machine you just clearned out. No matter what I did I couldn't get rid of this one bad entry, was driving me crazy, even rebooted the switching hub and router thinking maybe they were hanging onto it. Then I found it was only hosed for the virtual interface, but not the main address. I looked at the initialization file for virtual interfaces and it was hard-coded into the file. Fixed that, rebooted, cleared all the bad entires, and now everything appears to be back to normal.