Using PPP with MachTen

MachTen PPP (Point-to-Point Protocol) provides a serial interface between remote Internet Packet routers and a local MachTen system. The result is a local system remotely "attached" to an internet as if it were locally hosted on that net. The local MachTen system is able to enjoy full internet TCP/IP capabilities and at the same time operate over what amounts to a serial line or dial-in communications umbilical link. MachTen PPP is used to manage packet level communications over that point-to-point data communications umbilical cord.

PPP client and server implementations are used in pairs at each end of a point-to-point link to setup, manage and tear down an Internet Protocol communication link. MachTen PPP contains parameterization for the specification of Internet Addresses for each end of the serial link, text scripting for the login and startup of a PPP server on a remote system, and specification of link integrity packets to signal the absence of PPP operations at the other end of the link.

MachTen PPP can be configured as either a PPP client or a PPP server. This document contains step-by-step instructions for setting up a MachTen PPP client and a MachTen PPP server. It presents important information for configuring MachTen Modems which is possibly the largest problem in setting up a PPP link. In addition it presents the results of a series of performance measurements over different serial and dial-in links so that you may know what to expect in performance terms from a particular PPP installation.

MachTen PPP Setup

The five steps to creating a PPP link are: Pre-installed equipment or services will make some steps unnecessary.

MachTen PPP Client and Server Operation

The MachTen program /usr/libexec/pppd functions as either a PPP client or a PPP server. To setup a PPP server a MachTen timesharing login is setup with a user name and a password. When a user logs into MachTen as the PPP user, rather than setting up a timesharing shell, the PPP user is configured to startup the /usr/libexec/pppd program with appropriate configuration for the fledgeling PPP link.

To contact a pre-configured PPP server, a MachTen PPP client must first establish some form physical link with a remote system. Typically this is accomplished with a dial-in modem, but hardwire lines directly connecting two serial ports, ISDN or Frame Relay data communications links all serve the purpose of providing character-by-character communications between a MachTen PPP client system and a PPP server.

Most of the problems that arise in connecting a PPP client and server are in the initial setup and configuration of the communications link and in the proper interfacing of that link to a MachTen Macintosh. See MachTen Modem Interfacing for common Macintosh-Modem problems and their solutions.

To aid in the testing and setup of a point-to-point link, the MachTen tip program is often used to establish a connection over the serial link, to log into the remote system with a timesharing login and to generally test the link performance in qualitative terms.

PPP Client Operations

Once the basic link operations have been tested either with TIP or by other means, the results of those tests can be used to setup a PPP client. The PPP client is established by running the /usr/libexec/pppd program with proper parameterization. Typically, this setup is stored in a MachTen shell script which can be executed from the MachTen command line, from a user login script or from system level execution scripts. The PPP client setup contains two parts: a text script to login into the remote system as a PPP user and parameterization of the /usr/libexec/pppd once the remote login has been successfully accomplished. To facillitate PPP client setup MachTen includes a prototype PPP client script /etc/pppclient which simplifies PPP client execution.

Once the PPP client shell script has been successfully executed, the PPP link has been established and traditional TCP/IP operations can be directed to the link. During the testing phase of a PPP link configuration, the MachTen ping program is often used to bounce ICMP packets off of remote TCP/IP hosts to pre-flight test the basic connectivity and routing of the new PPP link. In addition, the traceroute program can be used to analyze the route packets are taking between two TCP implementations.

PPP routing is possibly the next most prevalent cause of PPP link failure. The netstat can be used to isolate PPP packet flow. See PPP routing and Viewing link statistics for more information.

Once TCP/IP operations have been tested successfully, the PPP link is operational and should be used link any other TCP/IP network interface.

PPP Server Operations

PPP servers are the mirror image of their clients. They must be pre-configured and passive awaiting requests for service. MachTen PPP servers are executed as the execution program for a special MachTen login. While any login name may be choosen, typically, the username ppp is choosen as a login to initiate MachTen PPP service. The end result of a successful PPP login is the execution of the /etc/pppserver script. This script is a simplified counterpart of the /etc/pppclient script used to start /usr/libexec/pppd for MachTen PPP clients.

In addition to pre-configuration of the ppp login, MachTen PPP servers must pre-condition local communications hardware to accept an inbound connection. While this may take a number of different forms, many times it requires the pre-configuration of a modem to accept incoming phone calls.

Once both communications hardware and ppp login software are configured properly, testing may begin with a PPP client. Testing may be sensibly organized to use a pre-tested PPP client with another remote PPP server.

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