Archive for Network Technology

Ubuntu Not Recognizing Changes To /etc/hosts

ah-ha

A moment ago, I finally figured out why changes to /etc/hosts on my local Ubuntu desktop were not being honored. In the past, it worked just fine, as expected, but this morning, it refused to recognize changes. I searched all over the web and found lots of people with the same problem, but no solutions. Plenty of helpful suggestions, mind you, but nothing would work for the folks who tried them. So, the solution? My NSCD was caching it. Perhaps there was a default value change recently, or maybe I just somehow never noticed it before because I’d add the entry prior to trying to work with the host. Not sure the ultimate reason, but the fix is in:

sudo vim /etc/nscd.conf

Change:
enable-cache hosts yes
…. to:
enable-cache hosts no

And then restart NSCD:

sudo service nscd restart

Voila! Finally, I can get on with my work for the day.

Windows Server Says, “Network Cable Unplugged” When It’s Not?!?

Once again, stuck managing a Windows box. Yeah, I know, I’ll whine, bitch, moan, and cry you a river another time.

The Problem: Using the secondary NIC (PNET/VLAN), I found a lock of packet collision during negotiation, handshaking, and identification, causing Windows to give up and basically say, “well, since it’s not working, the cable must physically have been removed, because there’s no way I could ever be wrong.”

Wro…. err…. incorrect, Windows. (You’re wrong.)

The Discoveries: The truth was, at least in my case, that it wasn’t properly handling the gigabit capabilities of the card on the box. I’m not the administrator for these machines (though they’re housed in our datacenter), so I can’t be certain that nothing had changed recently, but their staff said nothing at all had been modified. Perhaps that really was the case, and nothing had been changed — Windows has been known to do stranger things than this, of course, sometimes out of the blue.

The Solution (for my case): Go to the screen where you can view your network adapters (your version of Windows dictates the path of navigation, hence the ambiguity). Next, right-click the adapter with the “Network Cable Unplugged” message and click “Properties.” Click the appropriate button to configure the network adapter. Then click the tab on that dialog for “Settings” or something of the like (sorry, but I logged out in a hurry, so this is from memory), and you’ll see a list of parameters on the left, with their values on the right. Find one related to speed and duplex, and if you see it set to “Auto” or similar, drop it to “100Mbps Full Duplex” and click OK. Close the properties dialog by clicking “OK” and see if the settings are already bringing the network adapter back online. If not, disable and re-enable the adapter, and – if it was indeed the same issue – you should be back online within a few seconds.