This evenings planned maintenance activity is taking longer than expected because just as I rebooted the main file server, the Ethernet cable connecting it to the switch decided to die.
I had to make a trip to the co-location facility to troubleshoot. Since I had just upgraded the kernel my initial assumption was the new kernel had problems with the Ethernet driver or bridge.
After rolling back to the previous kernel and still not having network connectivity, I noticed the LEDs on the Ethernet port were dark. I replaced the cable and they came back to life.
I then upgraded back to the newer kernel and everything continued to work. I am
now doing imaging on shellx, ftp/www, and mail.