Networking / Beginners

Remote Access Service (RAS)

RAS has become a major part of network solutions, using the telephone lines as the physical medium to transfer the data. RAS is a service that allows remote clients to connect to the server over a modem using a RAS-based protocol such as the Serial Line Internet Protocol (SLIP) or the newer Point-to-Point Protocol (PPP).

PPP can run with network protocols such as TCP/IP, IPX/SPX, and NetBEUI; SLIP only supports TCP/IP. This means that you will need to ensure that the client has the network protocol of the destination installed and that the RAS protocol (SLIP or PPP) can run with that network protocol. For example, if the remote network is running IPX/SPX, you will need to ensure that the user who wishes to dial up to that network is running IPX/SPX and that the RAS protocol supports IPX/SPX (PPP in this case).

SLIP and PPP are two communications protocols used by RAS that are used to connect a computer to a remote network through a serial connection using a device such as a modem. When the computer dials up to the remote network, it is treated as an actual node on the network like any other networking device. This setup enables users to run network applications from home as though they were on the network.

SLIP and PPP are fairly similar protocols as far as the overall goal, but they differ in their implementation. They use some of the same underlying technologies, but PPP is newer and better suited for today's expanding networks. The following sections discuss each protocol-how it works, and some of its advantages.

Serial Line Internet Protocol (SLIP)

The Serial Line Internet Protocol (SLIP) is a communications protocol used for making a TCP/IP connection over a serial interface to a remote network. SLIP was designed for connecting to remote UNIX servers across a standard phone line. This protocol was one of the first of its kind, enabling a remote network connection to be established over a standard phone line.

SLIP was designed when TCP/IP was the only network protocol commonly used by all UNIX platforms. Although it is still in use today, SLIP has mostly been replaced by PPP. A user can be configured as a SLIP client with Windows 2000/XP/2003, but Windows cannot be a SLIP dial-in server.

Using SLIP to Connect to a Remote Host

To set up a SLIP client in Windows, you must first create the new connection within your Network Connections dialog box. Once you have created the dial-up network connection, you will need to configure its properties and change it from using PPP (the default in Windows) to using the SLIP protocol.

You might notice that the Settings button is grayed out once you switch from PPP to SLIP; this is because SLIP provides no support for advanced features such as software compression, password encryption, or multilink functionality. Select Internet Protocol (TCP/IP) and click Properties to configure parameters such as the IP address, DNS server addresses, default gateway, and IP header compression.

SLIP is a very simple serial-based protocol. It does not provide the complexity that others, such as PPP, do. Although that can be an advantage, SLIP unfortunately does not include the feature set of other protocols. For example, it does not support option negotiation or error detection during the session setup. It cannot be assigned an address from a DHCP server-it must use static addresses. It also cannot negotiate the authentication method. Issues such as these have helped define the new protocols that are emerging because a given functionality does not exist in SLIP.

The following list summarizes the characteristics of SLIP:

  • Runs only with TCP/IP.
  • Does not support DHCP functionality.
  • Does not support compression or password encryption.
  • Used to connect to older UNIX or Linux SLIP servers.
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