PPP Dialin Service

PPP is an internet standard for the transmission of IP packets over a serial port. Enabling a serial port for PPP allows the NetRS web configuration interface, and other network services, to be accessed over a serial port. The NetRS implements two PPP methods. This page describes PPP Dialin, which is usually refered to simply as PPP. (The alternative PPP Dialout is discussed elsewhere.)

When a port is configured to support PPP Dialin, an external computer runs a PPP Client program which initiates the connection, often via a telephone modem. The typical use for this is to allow the external computer to set up a private networking connection to the NetRS so that programs (like a web browser) running on the computer can access network services (like the web server) on the NetRS. More complex setups are possible, but they are beyond the scope of this document.

When configurating a NetRS PPP Dialin connection, two IP addresses must be specified. The values for these are entered into the PPP Dialin configuration on the NetRS. These addresses are named from the point of view of the NetRS side of the connection. The Local IP Address is the network address that will be used by client programs on the remote computer to contact the NetRS. For example, the Local IP Address could be typed into a remote web-browser when attempting to access the local webserver on the NetRS. The Remote IP Address is used inside the PPP programs on either side of the PPP link to implement the routing of PPP packets. Normally the user will never directly use the Remote IP Address.

PPP addresses probably should be set up in a private address space. The IANA, Internet Assigned Numbers Authority, has reserved three blocks of IP addresses for this purpose. The document Address Allocation for Private Internets discusses this and can be found at the following location:

http://www.isi.edu/in-notes/rfc1918.txt

If PPP is used with multiple NetRS units, care must be taken in the assignment of the Local and Remote IP addresses. If the NetRS systems are configured such that each Local and Remote address pair is unique, then it is possible to connect to multiple NetRS units at the same time. But If the same Local and Remote IP address pair is specified for each NetRS, then care must be taken to ensure that only one NetRS is connected to the external computer at a time.


PPP Dialin Configuration

PPP Dialin connections are configured via the Port Configuration pages. Select the serial port that is to be used, select the PPP service and specify the Baud rate to be used for the connection. Enter the Local IP Address and Remote IP Address. Then select the Connection type:

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