What is "slirp"

Slirp (sometimes capitalized SLiRP) is a software program that emulates a PPP, SLIP, or CSLIP connection to the Internet via a shell account. It is largely obsolete for its original purpose, as dedicated dial-up PPP connections and broadband Internet access have in turn become widely available and inexpensive. It remains useful for connecting mobile devices, such as PDAs, via their serial ports. Another significant current use-case is firewall piercing/ port forwarding, which is typically but not necessarily done by way of an SSH connection on which port forwarding is restricted.