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DECnet - MAC address - SCSSYSTEMID Calculator

This is a simple javascript tool to convert between DECnet addresses and MAC addresses of ethernet network adapters connected to DECnet networks. Enter either the DECnet Area and Node number, or the MAC address below. The VMS SYSGEN parameter SCSSYSTEMID is also calculated and displayed based on the input.

DECnet Area (1-63) and Node (1-1023):
MAC Address:
AA-00-04-00- -  


Check for a DECnet node at HECnet Node Status on QCOCAL VAXserver 3900 OpenVMS 7.3 »

Tweet to @OpenVMS_DECnet

SANYALnet Labs - Hobbyist Systems

Introduction to DECnet addressing

DECnet addresses are two numbers, expressed as <AREA>.<NODE> that fit in 2 bytes (16 bits) as follows:

In the world of DECnet, the six-byte MAC address of an ethernet adapter is keyed to the DECnet address of the node as follows:

Thus the lowest possible DECnet address 1.1 requires the network adapter's MAC address to be AA-00-04-00-01-04. For DECnet address 1.1, the six-bit AREA in binary is 000001. The 10-bit NODE is binary 0000000001. Therefore the 16-bit DECnet address in binary is 0000010000000001, with the two bytes then being 00000100 and 00000001. Swapping these two bytes and expressing in hexadecimal produces 0x01 and 0x04 which are the last two bytes of the MAC address of the ethernet adapter.

The highest possible DECnet address 63.1023 requires the MAC address to be AA-00-04-00-FF-FF.

SCSSYSTEMID is a SYSGEN parameter used on OpenVMS systems. It needs to be set to the value of (AREA*1024)+NODE, which is the same as the value of six Area bits followed by ten Node bits taken as a 16-bit integer.

The design of DECnet, its protocols and related documentation are available online at The DECnet Phase IV Specifications.

SANYALnet Labs

That is just a name I have given my disorganized bunch of computers and electronics hobby projects; it is nebulous and does not really mean anything. Equivalent to "junk in the basement."


I try to maintain a list and descriptions of the numerous operating systems and hardware I play around with at my Freeshell/SDF page. The DECnet network currently consists of the following nodes, all of them connected to HECnet (the global hobbyist DECnet):

Node Name DECnet address Hardware and Operating System
IMPVAX 31.1 VAX 3900, OpenVMS 7.3
QCOCAL 31.10 VAX 3900, OpenVMS 7.3
CLOUDY 31.11 VAX 11/780, OpenVMS 7.3
JUICHI 31.12 PDP-11/24, RSX-11M Plus 4.6
FEDACH 31.13 i386, Linux Ubuntu 14.04, DECnet-Linux
FOMFOR 31.14 i386, Linux Ubuntu 14.04, DECnet-Linux
OSTARA 31.15 VAX 3900, DEC ULTRIX 4.0
WEXPEE 31.16 i386, Windows Server 2003, DECnet Pathworks
ENTEE4 31.17 i386, Windows NT 4.0 Server, DECnet Pathworks
RAPTOR 31.18 DEC AlphaServer ES40, OpenVMS Alpha 8.3
MACOS9 31.19 Power Macintosh 9500 / PowerPC G4, Apple MacOS 9, Digital Pathworks for Macintosh
WFW311 31.20 i386, Windows for Workgroups WFW 3.11, DECnet Pathworks for DOS and Windows
WXPEE2 31.21 i386, Windows XP Professional, DECnet Pathworks
TRU64 31.22 DEC AlphaServer 400 4/166, Digital Tru64 Unix 5.0 Alpha
XLVII 31.23 VAX 8600, VAX VMS 4.7
TSTVAX 31.24 VAX 3900, OpenVMS 7.3
W2000S 31.26 i386, Windows 2000 Server, DECnet Pathworks
MACOS7 31.27 Macintosh IIci / Motorola 68030, Apple MacOS System 7.5.5, Thursby TSSnet for Macintosh
RST101 31.28 PDP-11/73, RSTS/E 10.1-L, DECnet/E 4.1
TWENEX 31.29 DEC PDP-10, TOPS-20 v7.1
SHAKTI 31.50 Cisco 7206VXR, IOS 12.3(15) DECnet, AppleTalk Router
MOKSHA 31.1020 Cisco 7206VXR, IOS 12.3(15) DECnet, AppleTalk Router
IMPRTR 31.1023 Cisco 7206VXR, IOS 12.3(15) DECnet, AppleTalk Router, GRE Tunnels to other DECnet Area Routers
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You use any information on this website totally at your own risk. This a private hobbyist server with potentially everything being logged. There is absolutely no assurance of any kind whatsoever, no assumptions can be made about any sort of accuracy, privacy, security, availability and data retention. This applies to all my hobbyist servers mentioned here and elsewhere.