(The situation is this: I pay for a second dynamic IP address. Until a few weeks ago, I was using one on a NAT box and another on a Mac Mini. I took the Mini down in preparation for repurposing a different machine. Today, finally, everything was in place to bring that machine up. And it couldn't get an IP address from RCN. It's not a cable problem: With all the same cabling, but my own DHCP server in place of the cable modem, it gets an address just fine. The NAT box is still getting its address just fine. I haven't yet run tcpdump — I do that infrequently enough anymore that I'll have to RTFM first, and I didn't have time today. But I will of course do so before I call RCN. I'm reminded of the bad old days, when you had to phone your ISP with the new MAC address to change machines. Seems unlikely — but depending on what tcpdump shows, it may be my best working theory.)
At any rate, if I do end up having to call them, I'd really appreciate being able to route directly to someone with a clue. Anyone have a secret formula?