This part is a kind of semiconductor called KSZ8721BL.

Function of this product has 3.3V Single Power Supply 10/100Base-TX/FX MII Physical Layer Transceiver.

Manufacturers : Micrel Semiconductor

Image and pinout :

Some of the text within the PDF file :

KS8721BL/SL Micrel KS8721BL/SL 3.3V Single Power Supply 10/100BASE-TX/FX MII Physical Layer Transceiver Rev. 1.2 General Description Operating with a 2.5V core to meet low-voltage and low-power requirements, the KS8721BL and KS8721SL are 10BASET/100BASE-TX/FX Physical Layer Transceivers that use MII and RMII interfaces to transmit and receive data. They contain 10BASE-T Physical Medium Attachment (PMA), Physical Medium Dependent (PMD), and Physical Coding Sub-layer (PCS) functions. The KS8721BL/SL also have on-chip 10BASE-T output filtering. This eliminates the need for external filters and allows a single set of line magnetics to be used to meet requirements for both 100BASE-TX and 10BASE-T. The KS8721BL/SL automatically configures itself for 100 or 10Mbps and f [ ... ]

KSZ8721BL PDF Datasheet Download