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Developer(s) Danny Gasparovski, Kelly Price (maintainer)
Initial release March 30, 1995
Stable release 1.0.17 / January 8, 2006
Operating system Unix-like
Platform shell account
Type Dial-up access
License BSD-like license

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 has also been used for connecting mobile devices, such as PDAs, via their serial ports.


Shell accounts normally only allow the use of command line or text-based software, but by logging into a shell account and running Slirp on the remote server, a user can transform their shell account into a SLIP/PPP connection, allowing them to run any TCP/IP-based application—including standard GUI software such as the formerly popular Netscape Navigator—on their computer. This was especially useful in the 1990s because simple shell accounts were less expensive and/or more widely available than full SLIP/PPP accounts.[1]

In the mid-1990s, numerous universities provided dial-up shell accounts (to their faculty, staff, and students). These command line-only connections became more versatile with SLIP/PPP, enabling the use of arbitrary TCP/IP-based applications. Many guides to using university dial-up connections with Slirp were published online (e.g. [1], [2], [3], [4]). Use of TCP/IP emulations software like Slirp, and its commercial competitor TIA was banned by some shell account providers, who believed its users violated their terms of service or consumed too much bandwidth.[2][3]

Slirp is also useful for connecting PDAs and other mobile devices to the Internet: by connecting such a device to a computer running Slirp, via a serial cable or USB, the mobile device can connect to the Internet.[4]


Unlike a true SLIP/PPP connection, provided by a dedicated server, a Slirp connection does not strictly obey the principle of end-to-end connectivity envisioned by the Internet Protocol suite. The remote end of the connection, running on the shell account, cannot allocate a new IP address and route traffic to it.[5] Thus the local computer cannot accept arbitrary incoming connections, although Slirp can use port forwarding to accept incoming traffic for specific ports.

This limitation is similar to that of network address translation. It does provide enhanced security as a side effect, effectively acting as a firewall between the local computer and the Internet.[5]

Current status[edit]

Slirp is free software licensed under a BSD-like license by its original author. After the original author stopped maintaining it, Kelly Price took over as maintainer.[6] However, there have been no further releases since 2006. Debian maintainers have taken over some maintenance tasks, such as modifying Slirp to work correctly on 64-bit computers.[7]

See also[edit]


  1. ^ Jim Knoble (1996-08-01). "Almost Internet with SLiRP and PPP". Linux Journal. Retrieved 2009-08-28. 
  2. ^ Craig J. Miller (1995-03-15). "Intermind discussion of TIA on TENET". Retrieved 2009-08-31. 
  3. ^ "Everybody's Internet Update (section 1.5)". Electronic Frontier Foundation. September 1994. Retrieved 2009-08-31. 
  4. ^ Kelly Price. "Slirp Maintenance Project home page". Retrieved 2009-08-31. 
  5. ^ a b Glen Reesor (2001-02-21). "SLIP/PPP Emulator mini-HOWTO". Retrieved 2009-08-29. 
  6. ^ Kelly Price. "Slirp FAQ". Retrieved 2009-08-28. 
  7. ^ "Debian Changelog slirp". Retrieved 2009-08-28. 

External links[edit]