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relationship between SCSSYSTEMID and decnet address


relationship between SCSSYSTEMID and decnet address

Dear all,

I would like to know if there is any relationship between sysgen parameter SCSSYSTEMID and decnet address.

As observed in my environment, the two values are in general the same for the VMS systems.

Is it required also to update the SCSSYSTEMID if i am going to change the decnet address?

And, if i have to change the SCSSYSTEMID, what associated changes I have to applied to the clustered nodes?

Best Regards,
Bradford Hamilton
Regular Advisor

Re: relationship between SCSSYSTEMID and decnet address

>I would like to know if there is any >relationship between sysgen parameter >SCSSYSTEMID and decnet address.

Yes. SCSSYSTEMID = (DECnet area *1024) + node number; thus, DECnet address 1.1 = SCSSYSTEMID 1025.

>Best Regards,

Bruce Vinson
Occasional Visitor

Re: relationship between SCSSYSTEMID and decnet address

As Brad pointed out SCSSYSTEMID is derived from the DECnet address.

To change the ID, make the change in MODPARAMS.DAT, run AUTOGEN to set the new value (one could do this via SYSGEN, but that's bad form), and reboot. The system will join the existing cluster, assuming the SCSSYSTEMID is unique in the same cluster. If you change the DECnet address, the SCSSYSTEMID should be changed also.

If DECnet is not used, which is becoming more and more common, and TCPIP is the only protocol, then the SCSSYSTEMSIDs of the clustered systems can be arbitrary, as long as they are unique within the cluster authorization scheme.
Keith Parris
Trusted Contributor

Re: relationship between SCSSYSTEMID and decnet address

Note that if you change only the SCSSYSTEMID value (or only the SCSNODE value) for a node (and do not change both at the same time to new, unique values), VMS cluster nodes which remain up and are still aware of a node having been in the cluster before with a match for one of these parameters (but not both) will detect this situation as an error and refuse to let the node back into the cluster.

So if you change SCSSYSTEMID and don't want to also change SCSNODE (which matches the DECnet node name and TCP/IP nodename) at the same time, do your AUTOGEN (as described in an earlier reply) to change the SCSSYSTEMID value for the next boot, then shut the node down and keep it down while you reboot any other cluster nodes with memory of the old SCSSYSTEMID/SCSNODE combination.

$SHOW CLUSTER/CONTINUOUS with ADD SYS_ID will show what node(s) a given cluster node is aware of having been in the cluster in the past, and what the node's SCSNODE (under the "NODE" heading) and SCSSYSTEMID ("SYS_ID" heading) values were at the time. (A node which has left the cluster is shown with "BRK_NON" under "STATUS", indicating that it is a non-member of the cluster after a "long break" in communications.)
Mike Naime
Honored Contributor

Re: relationship between SCSSYSTEMID and decnet address

If you are running TCPIP, the DECNET address also affects/sets the MAC address that is reported out the first TCPIP network port.

If you show your decnet address in DECNET_REGISTER. It lists the MAC ADDRESS that is seen by the network switch on the primary network port. Not the MAC address embedded in the NIC.

So, if you change your DECNET address. Let your network folks know that your MAC address associated with your IP adress will change.

VMS SAN mechanic