Ethernet Ping Location

Is the Arduino Ethernet's nature to respond to ping requests a feature of the wiznet chip, or is it in the Ethernet library?

Typically, base features (protocols) are built into the chipset. According to the SparkFun description page, so is the Wiznet 5100. This description says ICMP is built in the chip. Ping is and ICMP echo/echo response.

https://www.sparkfun.coma/products/9471

I hope this helps.