I confirmed (sort of, read on) that commenting out the $ipaddr2 line causes it to fail. After commenting out the $ipaddr2 assignment, the second arp_lookup() still worked. This was odd to me since I tested the snippet a bunch before I posted. I looked further up to the first print. Upon commenting out the first print, the second arp_lookup() failed to work. If I comment out the first print and the $ipaddr2 assignment, the second arp_lookup() no longer works. Odd.