Slirp
Encyclopedia
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. However, it remains useful for connecting mobile devices, such as PDA
s, via their serial port
s.
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.
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. http://www.wam.umd.edu/~toh/SLiRPMacPPP.html, http://fig.cox.miami.edu/Faculty/Tom/Newsletter/SLIRP.html, http://users.encs.concordia.ca/~dave/work/win95.html, http://www.businesslab.mtsu.edu/Lab/tectrain/slirp_w95.htm). 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
.
Slirp is also useful for connecting PDA
s 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.
. The remote end of the connection, running on the shell account, cannot allocate a new IP address
and route
traffic to it. Thus the local computer cannot accept arbitrary incoming connections, although Slirp can use port forwarding
to accept incoming traffic for specific port
s.
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.
licensed under a BSD-like license by its original author. After the original author stopped maintaining it, Kelly Price took over as maintainer, 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.
Point-to-Point Protocol
In networking, the Point-to-Point Protocol is a data link protocol commonly used in establishing a direct connection between two networking nodes...
, SLIP
Serial Line Internet Protocol
The Serial Line Internet Protocol is an encapsulation of the Internet Protocol designed to work over serial ports and modem connections. It is documented in RFC 1055...
, or CSLIP connection to the Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
via a shell account
Shell account
A shell account is a user account on a remote server which gives access to a shell via a command-line interface protocol such as telnet or ssh....
. It is largely obsolete for its original purpose, as dedicated dial-up PPP connections and broadband Internet access
Broadband Internet access
Broadband Internet access, often shortened to just "broadband", is a high data rate, low-latency connection to the Internet— typically contrasted with dial-up access using a 56 kbit/s modem or satellite Internet with inherently high latency....
have in turn become widely available and inexpensive. However, it remains useful for connecting mobile devices, such as PDA
Personal digital assistant
A personal digital assistant , also known as a palmtop computer, or personal data assistant, is a mobile device that functions as a personal information manager. Current PDAs often have the ability to connect to the Internet...
s, via their serial port
Serial port
In computing, a serial port is a serial communication physical interface through which information transfers in or out one bit at a time...
s.
Usage
Shell accounts normally only allow the use of command line or text-basedText user interface
TUI short for: Text User Interface or Textual User Interface , is a retronym that was coined sometime after the invention of graphical user interfaces, to distinguish them from text-based user interfaces...
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
Gui
Gui or guee is a generic term to refer to grilled dishes in Korean cuisine. These most commonly have meat or fish as their primary ingredient, but may in some cases also comprise grilled vegetables or other vegetarian ingredients. The term derives from the verb, "gupda" in Korean, which literally...
software such as the formerly popular Netscape Navigator
Netscape Navigator
Netscape Navigator was a proprietary web browser that was popular in the 1990s. It was the flagship product of the Netscape Communications Corporation and the dominant web browser in terms of usage share, although by 2002 its usage had almost disappeared...
—on their computer. This was especially useful in the 1990s
1990s
File:1990s decade montage.png|From left, clockwise: The Hubble Space Telescope floats in space after it was taken up in 1990; American F-16s and F-15s fly over burning oil fields and the USA Lexie in Operation Desert Storm, also known as the 1991 Gulf War; The signing of the Oslo Accords on...
because simple shell accounts were less expensive and/or more widely available than full SLIP/PPP accounts.
In the mid-1990s, numerous universities provided dial-up
Dial-up access
Dial-up Internet access is a form of Internet access that uses the facilities of the public switched telephone network to establish a dialled connection to an Internet service provider via telephone lines...
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. http://www.wam.umd.edu/~toh/SLiRPMacPPP.html, http://fig.cox.miami.edu/Faculty/Tom/Newsletter/SLIRP.html, http://users.encs.concordia.ca/~dave/work/win95.html, http://www.businesslab.mtsu.edu/Lab/tectrain/slirp_w95.htm). Use of TCP/IP emulations software like Slirp, and its commercial competitor TIA
The Internet Adapter
The Internet Adapter was software created by Cyberspace Development in 1993 to allow SLIP connections over a shell account. PPP was added in 1995, by which time the software was marketed and sold by Intermind of Seattle...
was banned by some shell account providers, who believed its users violated their terms of service
Terms of service
Terms of service are rules which one must agree to abide by in order to use a service. Unless in violation of consumer protection laws, such terms are usually legally binding...
or consumed too much bandwidth
Bandwidth (computing)
In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
.
Slirp is also useful for connecting PDA
Personal digital assistant
A personal digital assistant , also known as a palmtop computer, or personal data assistant, is a mobile device that functions as a personal information manager. Current PDAs often have the ability to connect to the Internet...
s and other mobile devices to the Internet: by connecting such a device to a computer running Slirp, via a serial cable
Serial cable
A serial cable is a cable that can be used to transfer information between two devices using serial communication. The form of connectors depends on the particular PHY used...
or USB, the mobile device can connect to the Internet.
Limitations
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 suiteInternet protocol suite
The Internet protocol suite is the set of communications protocols used for the Internet and other similar networks. It is commonly known as TCP/IP from its most important protocols: Transmission Control Protocol and Internet Protocol , which were the first networking protocols defined in this...
. The remote end of the connection, running on the shell account, cannot allocate a new IP address
IP address
An Internet Protocol address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing...
and route
Routing
Routing is the process of selecting paths in a network along which to send network traffic. Routing is performed for many kinds of networks, including the telephone network , electronic data networks , and transportation networks...
traffic to it. Thus the local computer cannot accept arbitrary incoming connections, although Slirp can use port forwarding
Port forwarding
Port forwarding or port mapping is a name given to the combined technique of# translating the address and/or port number of a packet to a new destination# possibly accepting such packet in a packet filter...
to accept incoming traffic for specific port
TCP and UDP port
In computer networking, a port is an application-specific or process-specific software construct serving as a communications endpoint in a computer's host operating system. A port is associated with an IP address of the host, as well as the type of protocol used for communication...
s.
This limitation is similar to that of network address translation
Network address translation
In computer networking, network address translation is the process of modifying IP address information in IP packet headers while in transit across a traffic routing device....
. It does provide enhanced security as a side effect
Side effect (disambiguation)
Side effect is an effect that is secondary to the one intended.Side effect may also refer to:* Therapeutic effect, an unintended but desirable consequence of medical treatment...
, effectively acting as a firewall
Firewall (computing)
A firewall is a device or set of devices designed to permit or deny network transmissions based upon a set of rules and is frequently used to protect networks from unauthorized access while permitting legitimate communications to pass....
between the local computer and the Internet.
Current status
Slirp is free softwareFree software
Free software, software libre or libre software is software that can be used, studied, and modified without restriction, and which can be copied and redistributed in modified or unmodified form either without restriction, or with restrictions that only ensure that further recipients can also do...
licensed under a BSD-like license by its original author. After the original author stopped maintaining it, Kelly Price took over as maintainer, however there have been no further releases since 2006. Debian
Debian
Debian is a computer operating system composed of software packages released as free and open source software primarily under the GNU General Public License along with other free software licenses. Debian GNU/Linux, which includes the GNU OS tools and Linux kernel, is a popular and influential...
maintainers have taken over some maintenance tasks, such as modifying Slirp to work correctly on 64-bit
64-bit
64-bit is a word size that defines certain classes of computer architecture, buses, memory and CPUs, and by extension the software that runs on them. 64-bit CPUs have existed in supercomputers since the 1970s and in RISC-based workstations and servers since the early 1990s...
computers.
See also
- PPP daemon
- The Internet AdapterThe Internet AdapterThe Internet Adapter was software created by Cyberspace Development in 1993 to allow SLIP connections over a shell account. PPP was added in 1995, by which time the software was marketed and sold by Intermind of Seattle...
, a commercial product that competed with Slirp
External links
- Slirp Maintenance Project, official site for recent versions of Slirp
- Latest version of Slirp (1.0.17) from Debian