Monday, April 1, 2019

Setting up a MULTINET TCP connection (DECnet over IP)

Supratim Sanyal's Blog: MULTINET TCP Tunnel - OpenVMS VAX Server DECnet over TCP/IP Link

Here is an example of a MULTINET:DECNET-CIRCUITS.COM file for Process Software's MULTINET TCP/IP for OpenVMS. This sets up a TCP connection to another MULTINET end-point for DECnet traffic to be tunneled under TCP/IP.

The "MULTINET CONFIGURE /DECNET" command seems to allow only UDP connections to be configured; if so, MULTINET:DECNET-CIRCUITS.COM needs to be hand-edited for the connections to be based on TCP instead of UDP.

Specifically, after using the normal configuration utility to set up a default UDP connection, the "multinet set /decnet" line in MULTINET:DECNET-CIRCUITS.COM has to be modified manually to use TCP. This is borne out by the relevant section from MultiNet DCL Command Reference which states that the "/TCP" switch is not supported by the normal configuration utility:

MULTINET SET /DECNETConfigures the DECnet TCPAx: devices for running DECnet-over-UDP circuits.
Specifies the number of buffers the driver preallocates for this device (by default, 6).
Shuts down and deletes a socket created with the socket() routine. After issuing a CLOSE command, the socket cannot be used again until the MULTINET SET/DECNET command is reissued.
Issues a connect() call to bind the remote address of the socket to the address specified in /REMOTE_ADDRESS.
Specifies the DECnet device name (by default, TCPA0:).
Controls the handling of out-of-order DECnet packets arriving via IP. Prior to VMS V4.7, DECnet could not handle packets arriving out-of-order and would drop the line if it received them. If you have any VMS V4.6 or earlier systems in your DECnet network with which you are communicating, you must use the /FILTER_OUT_OF_ORDER=ON qualifier. The default action,
/FILTER_OUT_OF_ORDER=AUTOMATIC, selects the correct filtering based on the VMS version of the current system only.
Specifies that send() and recv() log a sample of the data passed through them to OPCOM. Use this qualifier only for debugging network problems.
Specifies that send() and recv() errors are logged to OPCOM. The default is to log all errors except these.
Specifies the UDP port number to use for communication (by default, 700).
Specifies the peer's IP address.
Specifies that DECnet is encapsulated in TCP instead of UDP. This mode is not supported by the normal configuration utility, but is of use over high-loss lines. LISTEN specifies that this end of the connection listens on the specified port; CONNECT specifies that this end attempts to connect to the listener on the specified port.
The MULTINET:DECNET-CIRCUITS.COM file below is from an actual SIMH MicroVAX 3900 running OpenVMS 7.3 and MULTINET version:

$ multinet show/version
Process Software MultiNet 5.5 Rev A, VAXserver 3900 Series, OpenVMS VAX V7.3

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