Use the nicinfo command:
/usr/sbin/nicinfo device
This utility displays information about the given network interface connection, or /dev/io-net/en0 if you don't specify one. The information includes the number of packets transmitted and received, collisions, and other errors, as follows:
3COM (90xC) 10BASE-T/100BASE-TX Ethernet Controller Physical Node ID ................. 000103 E8433F Current Physical Node ID ......... 000103 E8433F Media Rate ....................... 10.00 Mb/s half-duplex UTP MTU .............................. 1514 Lan .............................. 0 I/O Port Range ................... 0xA800 -> 0xA87F Hardware Interrupt ............... 0x7 Promiscuous ...................... Disabled Multicast ........................ Enabled Total Packets Txd OK ............. 1585370 Total Packets Txd Bad ............ 9 Total Packets Rxd OK ............. 11492102 Total Rx Errors .................. 0 Total Bytes Txd .................. 102023380 Total Bytes Rxd .................. 2252658488 Tx Collision Errors .............. 39598 Tx Collisions Errors (aborted) ... 0 Carrier Sense Lost on Tx ......... 0 FIFO Underruns During Tx ......... 0 Tx deferred ...................... 99673 Out of Window Collisions ......... 0 FIFO Overruns During Rx .......... 0 Alignment errors ................. 0 CRC errors ....................... 0.