Slirp

Slirp (sometimes capitalized SLiRP) is a software program that emulates a PPP, SLIP, or CSLIP connection to the Internet using a text-based shell account. Its original purpose became largely obsolete as dedicated dial-up PPP connections and broadband Internet access became widely available and inexpensive. It then found additional use in connecting mobile devices, such as PDAs, via their serial ports. Another significant use case is firewall piercing/port forwarding. One typical use of Slirp creates a general purpose network connection over a SSH session on which port forwarding is restricted. Another use case is to create external network connectivity for unprivileged containers.