Posted on in Networking
<acronym title="UniDirectional Link Detection">UDLD</acronym> is a Cisco protocol designed to detect and disable unidirectional links in Ethernet (fiber or twisted-pair). In the case of a radio-based Metro Ethernet ring, UDLD goes the extra mile in preventing Spanning-Tree loops and user service interruption.
In this simple network of …
Posted on in voice
When using Asterisk and a remote bank of <acronym title="Primary Rate Interface">PRI</acronym>s (or any other form of <acronym title="Public Switched Telephone Network">PSTN</acronym> connectivity for that matter), you may encounter an issue known as hairpinning. Hairpinning describes what happens when a call coming from …
Posted on in System Administration
A buddy of mine was recently setting up a new installation of Courier with virtual user support via MySQL. He ran into an issue when trying to get authdaemond to connect to a remote MySQL installation. No matter what he changed in authmysqlrc, the following kept appearing in his mail …
Posted on in System Administration
If you're like me, it probably seems obvious that command logging is an important part of system administration. Any change I make, whether it's on a router or server, is logged somewhere. Although folks give plenty of reasons why they don't use tools like sudo for super-user functions (inconvenience and …
Posted on in System Administration
Note: I recently had to prepare a Mac mini for use as a network testing device. The system was installed in a remote location and only reachable via SSH.
Important commands: hdiutil, installer, softwareupdate, shutdown
When preparing a system for production, there are three main tasks that need to be …
Posted on in Graphics Design
Transparent PNGs look simple when they work. They look amateurish when they do not.
The difference is usually not the PNG format itself. PNG supports transparency just fine. The problem is almost always the mask: hard edges, dirty pixels, color halos, or an export path that flattened the image against …
Posted on in System Administration
There was a time when adding a Mac OS X user from the command line meant talking
directly to NetInfo with nicl, copying a user template with ditto, and
hoping you did not fat-finger a UID. That was useful knowledge in 2007. It is
also very much not how I …
Posted on in Networking
Network configuration names are not decoration. They are operational metadata.
When something is broken at 2:00 a.m., the difference between ACL-EDGE-IN and
access-list is not aesthetic. It is the difference between narrowing the blast
radius quickly and spelunking through hundreds or thousands of lines of Cisco IOS
configuration …
