Troubleshooting

While troubleshooting a wireless issue, I mentioned offhand to another engineer that a particular MAC address was private. They immediately asked me “How did you know just by looking at it?” I said “Look at the second least significant bit of the most significant byte,” but quickly realized that needed a bit more explanation. “Private” MAC addresses, at least as implemented by Apple and Android, sets the locally-administered bit for their randomized addresses. RFC7042 section 2.1 specifies the “Local bit”: ...

One of my co-workers had provisioned a new appliance VM. It was having connectivity problems, so he asked me to look at it. Upon investigation, I found: absolutely no connectivity: RX Packets 0 on the interface. this was the first/only VM in this VLAN on this vCenter cluster they had just added this VLAN to the dvSwitch for this project So, I first checked what had changed most recently, the dvSwitch config. Everything looked correct. I compared it to other (working) VLANs, and saw no discrepancies. ...