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HOW TO: Determine the maximum number of concurrent Realport driver connections your Etherlite supports


How many concurrent Realport driver connections can be made to your EtherLite?


While most of our EtherLite products support up to 6 concurrent "host" connections, the connections do not have to be from hosts which are all running the same operating system. They can be made from any mixture of hosts, from any Operating Systems which support the Realport Driver.

Concurrent Host Connection Limits per Model:

  • EtherLite 2 units with older firmware will only support up to 2 concurrent host connections, while units with newer firmware may support up to 6.
  • The EtherLite 8 only supports up to 3 concurrent host connections.
  • All other EtherLite products support up to 6 concurrent host connections.

Note:  If a host has an EtherLite "configured", its connection to the Etherlite is live at all times.  Each driver connection counts against the limits listed above, whether or not the serial ports are actually in use.

Checking the number of Concurrent Host Connections:

You can verify what connections are currently live on the unit if you have an rlogin client on a Unix/Linux machine (verlog.exe in the Windows world) somewhere (telnet will NOT work).

Simply rlogin to the unit (no username or password) and then type the "sockets" command.

The current connections can be displayed like this:

    ? sockets
                   remote local
       remote ip     port  port    state       sRTT   sMDEV
    --------------- ----- ----- ------------ ------- -------     01023 00513 ESTABLISHED  00016ms 00816ms         00000 00771 LISTEN       00000ms 02880ms   01025 00771 ESTABLISHED  00128ms 00128ms

Check the "remote ip", "local port", and the "state" in the output.  The remote ip is the host owning the connection, and the local port gives information about what type of connection it is.  The local ports listed above have significance:  513 and 771.

TCP port 513 is the rlogin/verlog connection (only one allowed at a time on ANY EtherLite product) - used for diagnostic info.

TCP port 771 is the connection which the Realport driver uses - the connection necessary for the serial ports to be created on your Operating System. The state entry shown as LISTEN is the internal Etherlite server which waits for new driver connections.  This is why it also listens on local port 771.

If an Etherlite unit has reached its maximum number of driver connections, the LISTEN entry will go away, until at least one driver connection is closed.

Orphaned Realport driver connections: These can be caused by server reboot, killing the Realport driver process other than gracefully, or at least 2 minutes of uninterrupted network communications have occurred with one or more of the connected Realport hosts.

Realport Driver requirements:

The only requirements for a Realport host to successfully make a driver connection to an EtherLite are:

  • The Etherlite has an IP address that can be reached by the Realport driver running on the host, whether static IP or bootp/DHCP service provided.
  • The host is running the Realport driver, and has unblocked access to the Etherlite on TCP 771 (default - but can be modified).
  • The Etherlite is NOT already at the maximum "concurrent host connection" limit for that model of EtherLite (See the Concurrent Host Connection Limits per Model section earlier in the article).

If a Realport host attempts to make a connection to an EtherLite which is out of available connections, the connection will simply fail. The driver will assume the unit is "offline", failing, or powered off, and will automatically start retrying until a connection is established. If an EtherLite has only one available connection remaining with two hosts trying to connect it, the connection will simply be given to the unit which establishes the driver connection first.  If the connection takes minutes without succeeding, an error is passed back to the application.

Exceeding the "Concurrent Host Limit" can be a big problem, as it may cause hosts to appear to "lose" and "regain" units or serial ports, seemingly at random. This can be very confusing, so paying close attention to the number of connections anytime an Etherlite is being shared by more than one Realport host will help to ensure a successful install.

Last updated: Jun 17, 2019

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