PPP Dialout Help

PPP Dialout is a method for establishing a continous connection to the internet using a Serial Port and a Modem to connect to an Internet Service Provider (ISP). Configuration for this function is very dependent on the exact characteristics of your modem, phone line and ISP. Thus, the guidelines written here are necessarily unspecific. Proper configuration will require a basic understanding of the pppd and chat processes as implemented in a Linux environment.

When properly configured for Dialout, the NetRS will automatically interact with the modem, dial the phone number of the ISP, log into the ISP's PPP server and establish a network connection using the PPP protocols. The connection will be maintained for as long as the phone line and ISP allow. If the connection is dropped, the NetRS will re-establish it (by dialing again, etc.) attempting to keep itself attached to the Internet as much as possible. Note that this is not an on demand only setup. The connection will be maintained regardless of actual network data flow.

The documentation below assumes that you are dialing directly into an ISP over a normal telephone modem. If your setup is significantly different from that model then the descriptions below might not accurately reflect the configuration you will need. For example, some radio modems negotiate their own PPP connection and much of the configuration that would normally be in the NetRS will actually reside inside the radio-modem. In such cases, items like the PAP or CHAP passwords might not be needed in the NetRS (although they may be required in the radio-modem itself) and the Options and Chat Script information could be significantly different.

Configuring the NetRS for PPP Dialout is a two step process. First the PPP Dialout Configuration page must be used to enter the ISP and Modem specific information needed to establish the PPP connection. Then the PPP Dialout function must be activated on the specific Serial Port to which the Modem is connected, using the Port Configuration Page. Once this is done, the automatic process will take over, dial the ISP, and establish the connection.

The PPP Dialout Configuration page allows the entry of several items.

Debugging PPP Dialout

As with any complex process, it is likely that your initial configuration of PPP Dialout will not succeed in creating a connection. When this happens you will need to debug your setup. On a normal Linux system, debugging a PPPD configuration would be done by launching the application from a terminal and viewing diagnostics on the terminal (standard output and standard error) as well as viewing various system log files.

The NetRS is a more constrained environment. The Console window is not available and the configuration files can't be directly viewed or edited. The primary debugging method is to view the system log files. These are available through the Browser-based interface's Testing-System Logs menu. By default, the main menu item Testing is not shown. To gain access, click five times on the Globe and Triangle image in the title bar of the NetRS GUI. That should add a new item to the main menu and switch the data frame to show the first submenu item which is System Logs. You will see a table showing a directory of the system log files. Clicking on a specific file name will display its contents below the table. For maximum information in the log file, turn on the debug option for pppd. This places debugging information in the system log file messages. You should be able to see lines there such as

    May 27 20:49:45 SysName pppd[341]: pppd 2.4.1 started by root, uid 0
    May 27 20:49:47 SysName chat[342]: send (ATZ^M)
    May 27 20:49:47 SysName chat[342]: expect (OK)
    May 27 20:50:32 SysName chat[342]: alarm
    May 27 20:50:32 SysName chat[342]: Failed
    May 27 20:50:32 SysName pppd[341]: Connect script failed

Note that the page displaying the messages file does not update automatically. Thus, to view the latest data you will have to refresh the data frame. A button is provided at the end of the page which automatically refreshes the display and scrolls to the end of the file.

Note that the pppd program will be restarted every time the configuration is accepted via the Browser GUI or Programmatic Interface. This restart will drop any existing ISP connection and begin the dialout process from the beginning. This happens regardless of whether actual changes are made to the configuration. Restarts for pppd are limited to one every 30 seconds.

Default Routes

Special attention must be paid to the way that PPP Dialout connections affect network routing. Generally, if PPP Dialout is used to set up a connection to an ISP, that connection will be used as the Default Route for wide area networking. This configuration expects that most network packets will flow over the PPP link. This mode is triggered by including the PPP option defaultroute in the list of Options. When this option is detected, any pre-existing default route setting will be deleted prior to starting the PPP Dialout connection. This can have unexpected consequences during the configuration phase as documented below.

In order to initially set up the PPP Dialout configuration, some other network link must be used. The GUI interface must be accessed from an external client (like a browser program), which must communicate over an IP link, such as the Ethernet port or a PPP Dialin connection. If that client program is NOT on a local subnet of the NetRS, then the client connection will be dependent on the default route setting. That setting will be erased when the PPP Dialout system is activated. Once that occurs, further communication over the old link will no longer be possible. In other words, once the wide area networking is switched over to PPP Dialout, the old networking connections can no longer be used for wide area networking. If this occurs then a remote browser client will no longer be able to communicate. A new browser connection will need to be created using the NetRS's new IP address via the ISP. This could be a serious problem if the new PPP Dialout configuration isn't quite right and needs to be debugged and adjusted.

Problems of this sort can be avoided by not using a wide area network connections during configuration of PPP Dialout. If the GUI is accessed from a client on the same subnet as the NetRS, the default route won't matter and communications over the old link will still be possible even if the PPP Dialout connection is misconfigured. A PPP Dialin link via the console port should work for this purpose. An ethernet link can also be used provided that the client browser is on the same subnet as the NetRS.

If a misconfigured PPP Dialout session is started which erases the default route, and GUI access is cut off, then it is not possible to reconfigure the PPP Dialout system using normal methods. Restoring network access will require physical access to the NetRS. A local PPP Dialin connection could be established using the front panel console port. Or the system controls could be reset to factory defaults by pressing the Power button for 30 seconds. Care should be taken to avoid the need for such a drastic measure. If possible, fully debug the PPP Dialout configuration using a local area network connection, prior to deploying the NetRS to a remote location.

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