 On Unix-like operating systems, traceroute sends, by default, a sequence of User Datagram Protocol (UDP) packets, with destination port numbers ranging from 33434 to 33534; the implementations of traceroute shipped with Linux, FreeBSD, NetBSD, OpenBSD, DragonFly BSD, and macOS include an option to use ICMP Echo Request packets ("-I"), or any arbitrary protocol ("-P") such as UDP, TCP using TCP SYN packets, or ICMP.On Windows, tracert sends ICMP Echo Request packets, rather than the UDP packets traceroute sends by default.The time-to-live (TTL) value, also known as "hop limit", is used in determining the intermediate routers being traversed towards the destination.