The Gigabit Ethernet interface of the Catalyst 2960 series switch fails in the PortPhiLoopback Packet Test of the power-on self-test (POST). This problem is observed in a Catalyst WS-C2960-48TT-L that runs Cisco IOS Software Release 12.2(25)SEE2.
These POST messages can appear:
POST: PortASIC Port Loopback Tests : Begin
POST: Failed PortPhiLoopback Packet Test asic_index 1 port_hardware_index 0
POST: PortASIC Port Loopback Tests : End, Status Passed
This issue is documented in Cisco bug ID CSCsg33994.
In order to resolve this issue, upgrade to Cisco IOS Software Release 12.2(35)SE or later, which can be downloaded from the LAN Switching Software page.