Which IP protocol is connectionless and unreliable?
Answer: udp -or- UDP
Explanation/Reference:
From http://en.wikipedia.org/wiki/User_Datagram_Protocol:
UDP uses a simple transmission model without implicit hand-shaking dialogues for providing reliability, ordering, or data integrity. Thus, UDP provides an unreliable service and datagrams may arrive out of order, appear duplicated, or go missing without notice. UDP assumes that error checking and correction is either not necessary or performed in the application, avoiding the overhead of such processing at the network interface level.