Duplex is Good, But Sometimes It Ain’t

With Charter starting to do some network upgrades around town (for their home users; not sure if I’ll get any boost out of it yet), I decided to see how my line speed was doing. I check it occasionally, but it’s been a while. Ya know, if it’s working, don’t bother it.

When I ran the speed test (from Speakeasy), I noticed that my downlink speed was about half what it should’ve been, which wasn’t what I expected. Charter’s gotten very active on Twitter lately, so I popped a tweet to Eric (@Umatter2Charter), who was quick to ask for some details. This was way before he gets in, but I check Twitter via my iPhone pretty frequently, so I saw his response later in the morning. He though that I’d need to be home to help troubleshoot, so I figured I’d pop another tweet his way once I got home… assuming there was still a problem.

I got home, found there was still a problem, and tweeted Eric about it…. and that’s when I thought to try the test from a different machine on the network. Sure ’nuff, the other machine was just fine. I was about to send Charter on a wild goose chase for something that was on my end. Not good. I tweeted Eric, and got him off the hook just in the nick of time before he called out the dogs. 🙂

As it ends up, my MacPro was sitting at an MTU of 1500, which is not the way it should’ve been set — everything in the house is using jumbo packets instead. Dunno how it got changed, but that wasn’t the culprit. It was my duplexing settings. Again, for some reason unknown to me, the MacPro was sitting at “full-duplex, flow control” instead of “full-duplex”, and through the arcanity of ethernet protocol compliance, that was slowing down my connection as the MacPro saw it. Once the settings were what I would’ve expected, all was well.

I sure wish I knew how things got ugly, but I’m just glad to get ’em fixed!