Okay, so last weekend my cable modem only intermittently had Internet access – then it finally gave up the ghost altogether. It wouldn’t even connect to my ISP (Cogeco) at all.

Talking to a technician resulted in the always popular “Have you turned it off and back on again? Did you reset it? What OS is it connected to?”. I may fall into the minority demographic of people who actually know what they’re doing when it comes to computers, but it’s always annoying to get this kind of a reponse. (Which is not to say that I don’t commonly ask those very questions of other people to whom I provide support. I can understand the reasoning behind it, it’s just annoying when you know, yourself, you don’t need to be on the receiving end of that particular exchange.)

In the end, I was told to get a replacement unit.

Several days later, Michelle got herself to the depot and picked one up. (A cute little RCA model.) I finally got home and plugged it in – while it connected to the ISP I got no activity at all.

I decided to plug it directly into my XP workstation (normally, it’s my Linux server) since that’s what, most commonly, these people want to deal with – even though actual connectivity between the modem and the ISP has nothing to do with the OS at the final, receiving end of things.

Switching my computer from its static IP to a dynamic IP resulted in it asking me to reboot (XP should never do this for such a change) and then some bizarre kind of RPC error. Obviously, there’s something wrong with my computer which I’ll have to deal with later – but it didn’t help that at the same time as my own computer was malfunctioning I had another technician on the phone.

Also, during my intitial contact with him, he asked me for my address. A quite simple request but, because of my flustered state, I drew a blank for about 20 seconds. It’s pretty embarrassing when you can’t tell somebody where you live…

Anyway, I finally set everything back to the configuration I normally have (with my Linux server getting an IP from the ISP) and read off the cable modem’s MAC address to the technician. It turned out that the woman who’d given Michelle the replacement unit must have typed it in wrong. She’d entered a “9” into the computer system rather than a “6”. So, while I was getting an IP, traffic to / from my connected system was blocked because my street address didn’t own that cable modem.

The technician fixed this and everything was then well. Almost.

I noticed that my Linux server was being flooded by strange “neighbour table overflow” messages. After 20 or 30 minutes of this, all networking on the server would stop. Some quick Googling, as well as some network traces, showed me that the problem was caused by an excessive amount of “ARP” traffic from the ISP, and a lack of the appropriate buffer memory on the server to handle it. A quick change to my server’s settings increased the buffer space from the minimum and that particular problem hasn’t happened since.

I can only wonder if this increased ARP traffic (which was not happening before) is somehow related to the failure of my old cable modem or not.

Aside from being offline for three days, and the frustration I went through, the only other downside is that we’ve lost some email – since our server was offline for longer than the normal “retry” period of time on messages that can’t get delivered.