Appendix II – Troubleshooting
AB06064 · Issue/Rev. 0.0 (5/06) Page 11
Appendix II – Troubleshooting TCP/IP Communications
Troubleshooting an Ethernet Connection
LED Indicators
The Link indicator on the Ethernet port (the green LED in top corner of microLoad.net main [MNET]
board) is a simple indication of the correct wiring of the physical connection. Most PC and router ports
also have a visible indicator when the connection is wired properly. If the Link light does not
illuminate, either the cable is the wrong type (i.e. a standard CAT-5 cable was used when a crossover
cable is needed or vice versa), the cable is faulty, or one of the RJ45 connector plugs is not inserted
completely into the jack. It is also possible but unlikely that one of the device ports has failed.
Eliminate the simplest first: double-check that the plugs are inserted fully; and that the cable type is
correct. You can often verify that a cable is standard (or not) by holding the two connectors from each
end of the cable together and viewing the wire colors within (most RJ45 connectors are clear plastic).
If the color pattern on the wires is identical on both ends of the cable, it is a standard cable.
PING Utility
To check the connection, Windows and most other network-able computers provide a low-level utility
called PING that issues a simple ICMP message to a remote device and awaits a response. To use
this utility in Windows, open a Command Prompt (DOS box) and type the command:
C:> PING 192.168.0.1
If the connection is successful, PING will report the total time from command to response. If it fails, a
timeout message will be displayed.
Advanced – Ethernet Diagnostic (Packet Sniffer) Utility
A useful tool for troubleshooting network communications is a packet sniffer. This type of utility
provides a mechanism to display the traffic being sent/received from the Ethernet port, and to dig
down to the lower levels to view MAC addresses and IP packet data.
An open source implementation of a packet sniffer utility, Ethereal, is available and can be
downloaded from the Web at http://www.ethereal.com/
. There are versions for Windows, Linux and
other platforms as well.
Troubleshooting a SLIP Connection
Using the Comm Monitor Diagnostic
The microLoad.net has a built-in diagnostic that displays traffic on the serial communications ports.
To access the Comm Monitor diagnostic, select Diagnostics Menu from the Main Menu, then scroll
using the arrow keys until the Comm Monitor selection is highlighted and press <Enter>. Then select
the communications port (1-3) that was configured for the SLIP connection. By examining the traffic it
is possible to determine if data is being received from the PC end, and whether a response is being
issued. You can ‘freeze’ the display, and scroll back and forth, and toggle ASCII and hex mode views
of the last 255 characters in the communications buffer.
CLIENT/CLIENTSERVER Handshake
When establishing a SLIP connection between two devices, Windows uses a non-standard
handshake to verify the device on the other end of the connection is compatible. Windows opens the
port and immediately sends the text “CLIENT” out the port, then waits for a response. Only the
response “CLIENTSERVER” will be accepted by Windows and allow the connection to be made. This
handshake should happen quickly and it will be visible on the Comm Monitor at least briefly if all is
functioning properly. If the Comm Monitor shows repeated CLIENT messages with no
CLIENTSERVER response, it is possible you have the IP addresses incorrect on one side or the
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