I discovered this problem while performing a routine binary upgrade from
9.1-RELEASE-p0. I checked
UPDATING and there were no warnings about known issues relating to my NIC.
freebsd-update -r 9.1-RELEASE upgrade freebsd-update install (reboot) freebsd-update install
After the reboot my primary network interface
no carrier. To make a long story short, the interface previously known as
em1 was now
em0 and the interface previously known as
em0 was no longer enumerated.
Scrolling back through the console messages showed:
em0: Setup of Shared code failed device_attach: em0 attach returned 6
pciconf -vlshowed that the interface previously enumerated as