DECnet Level 2 routing

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I have a few VAX/VMS DECnet machines with node addresses in Area 4. Their full DECnet node addresses are 4.200, 4.202, etc.  When I connect a DECnet machine in Area 33 (full address 33.13) to the same Ethernet segment, each of the Area 4 machines can see each other over DECnet, but the 33.13 machine can’t see the 4.202 machine and vice versa. They are all responding to LAT requests though, as I can use my DECserver 200 to login to any of them on a VT220 terminal.

The problem turns out to be that machines that only have a DECnet “end node” license installed are only able to directly communicate with other machines that have the same Area number.  Computers that have a different Area number (even those that are physically on the same Ethernet segment) will not be able to see each other.

The good news is that two computers on different Area numbers on the same Ethernet segment can be made to talk to each other if there are at least two “Phase IV level 2” routers on that segment.

To see if a machine is a Level 2 router, execute the “NCP>SHOW EXEC CHAR” command.  Look for the “Type” value.  It will be “area” if the machine is a Level 2 router. It will be “nonrouting IV” if it is just a Phase IV end node. It will be “routing IV” if it is a “Phase IV level 1” router.

There were two licence PAKs for DECnet on the VAX. The “end-node-only” PAK was called DVNETEND and the “routing” PAK was called DVNETRTG. Further information about these PAK’s can be found here at section 3.3.1 of the Guide to DECnet-VAX Neworking.

To change from “nonrouting IV” to “area”, you need to have a DVNETRTG licence PAK installed. Once you’ve verified that you have a DVNETRTG PAK installed (or installed one, if you didn’t previously have one), issue the following commands:

NCP>SET EXECUTOR STATE SHUT
%%%%%%%%%%%  OPCOM   1-MAY-2016 20:56:33.11  %%%%%%%%%%%
Message from user DECNET
DECnet shutting down

NCP>DEFINE EXECUTOR TYPE AREA
NCP>

We then need to exit NCP and restart DECnet as follows:

NCP>EXIT
$ @SYS$MANAGER:STARTNET.COM
%%%%%%%%%%%  OPCOM   1-MAY-2016 20:57:25.72  %%%%%%%%%%%
Message from user DECNET
DECnet starting

%RUN-S-PROC_ID, identification of created process is 00000210
%NCP-I-NOINFO, No information in database
%DCL-I-SUPERSEDE, previous value of MOM$SYSTEM has been superseded
%DCL-I-SUPERSEDE, previous value of MOM$SYSTEM_NOSOFTID has been superseded
%DCL-I-SUPERSEDE, previous value of MOM$SYSTEM_SOFTID has been superseded
%NCP-I-NOINFO, No information in database
%RUN-S-PROC_ID, identification of created process is 00000212
$

At this point you’ll see a bunch of OPCOM message flash past on the operator’s console.  The first will be a DECnet “circuit up” message, followed by a DECnet “adjacency up” message for each node that it sees.

You now should be able to use DECnet commands across the two areas.

This process is outlined in Section3.7.2 of the VMS Networking Manual, which is part of System Management Volume 5A.

The comments and information above are based on VMS version 5.3.

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