On Dell 1955 servers (and others) the network adapters are not enumerated
right. Physical port 1 becomes em1 and port 2 becomes em0. This is pretty annoying already, but makes it very hard to roll out a network installed farm and makes things confusing.
There's a DELL Document that describes the problem and solutions for FreeBSD,
but I could not find any for FreeBSD:
reassign to maintainer of em(4)
There have been numerous changes to PCI device enumeration since this issue was opened. If this machine is still testable, please try with the upcoming 10.2r release or beta when available and open a new ticket.