Thought you dodged the bullet?
Jun. 22nd, 2011 10:04 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
altivoThis one IS about DECnet.
What's DECnet? Well, it's a layered networking protocol that predates TCP/IP by nearly a decade (I think) and was developed by DEC to run over multiple physical media (from Ethernet to twisted pair phone lines) starting in the days of the PDP-11 and its relatives. DECnet came into its own along with the VAX line of computers, and survives to this day as a standard feature on OpenVMS for the Alpha and IA64 computers. DECnet protocol stacks are available on other platforms as well, including Linux and NetBSD I believe.
DECnet was built largely on the OSI (Open Systems Interconnect) standard, with some enhancements. With the rapid growth of the Internet, DECnet was eclipsed and began to fade. Various TCP/IP variants became available for OpenVMS and one of them was eventually incorporated by DEC and Compaq and became a normal feature even though it was technically an extra-cost "layered" product.
In any case, I last worked with DECnet in 1988. It has made a few advances since then, most notably elaborate configuration scripts that help you set it up. And that's a good thing because configuring DECnet is no simple task. It makes customizing Linux look like child's play, and isn't a task for the faint of heart or those who don't know networking jargon.
I've avoided the task for a couple of years but finally decided that I need to make DECnet work on my Alphas and emulated VAX machines. It took the better part of a day, but I finally got an emulated (SIMH) MicroVAX to talk native DECnet to a real Alpha as of this morning. I had most of it worked out yesterday, but needed some final details cleaned up.
DECnet is weird stuff. It uses Ethernet, but lacks the distinction between logical and physical addresses that we are used to seeing in TCP/IP. Instead of requiring a translation step (ARP protocol in TCP/IP) to match up the logical address with the physical MAC address, DECnet changes the MAC address to use a logical network address in the lowest32 16 bits. The rest of the MAC address is always the same: AA-00-04-00- must be a registered prefix that identifies DECnet devices.
The DECnet I knew in the 80s was Phase IV (introduced about 1982,) which supported a maximum of 64,449 nodes on any single network, but provided for routing between networks using dedicated routers and dynamic routing information. Later the addressing method was expanded (DECnet Phase V or DECnet Plus, about 1988) to support an astronomical number of nodes at the cost of incompatibility with Phase IV. Sound familiar? IPv4 and IPv6 anyone? DECnet Plus nodes can operate in Phase IV mode, though, as long as the network meets the necessary limitations.
Anyway, nodes C3P0 (MicroVAX) and ARCHIE (Alpha) are now exchanging data and handshakes on my LAN at home without a need for TCP/IP. Likewise, my two test VAX virtual machines, VULPES and CANIS, are doing the same on the library LAN. The next challenge? Get the native Linux host to speak DECnet to one of them, ultimately a virtual VAX hosted on the same physical hardware. Who needs video games when there's this kind of pointless challenge available?
What's DECnet? Well, it's a layered networking protocol that predates TCP/IP by nearly a decade (I think) and was developed by DEC to run over multiple physical media (from Ethernet to twisted pair phone lines) starting in the days of the PDP-11 and its relatives. DECnet came into its own along with the VAX line of computers, and survives to this day as a standard feature on OpenVMS for the Alpha and IA64 computers. DECnet protocol stacks are available on other platforms as well, including Linux and NetBSD I believe.
DECnet was built largely on the OSI (Open Systems Interconnect) standard, with some enhancements. With the rapid growth of the Internet, DECnet was eclipsed and began to fade. Various TCP/IP variants became available for OpenVMS and one of them was eventually incorporated by DEC and Compaq and became a normal feature even though it was technically an extra-cost "layered" product.
In any case, I last worked with DECnet in 1988. It has made a few advances since then, most notably elaborate configuration scripts that help you set it up. And that's a good thing because configuring DECnet is no simple task. It makes customizing Linux look like child's play, and isn't a task for the faint of heart or those who don't know networking jargon.
I've avoided the task for a couple of years but finally decided that I need to make DECnet work on my Alphas and emulated VAX machines. It took the better part of a day, but I finally got an emulated (SIMH) MicroVAX to talk native DECnet to a real Alpha as of this morning. I had most of it worked out yesterday, but needed some final details cleaned up.
DECnet is weird stuff. It uses Ethernet, but lacks the distinction between logical and physical addresses that we are used to seeing in TCP/IP. Instead of requiring a translation step (ARP protocol in TCP/IP) to match up the logical address with the physical MAC address, DECnet changes the MAC address to use a logical network address in the lowest
The DECnet I knew in the 80s was Phase IV (introduced about 1982,) which supported a maximum of 64,449 nodes on any single network, but provided for routing between networks using dedicated routers and dynamic routing information. Later the addressing method was expanded (DECnet Phase V or DECnet Plus, about 1988) to support an astronomical number of nodes at the cost of incompatibility with Phase IV. Sound familiar? IPv4 and IPv6 anyone? DECnet Plus nodes can operate in Phase IV mode, though, as long as the network meets the necessary limitations.
Anyway, nodes C3P0 (MicroVAX) and ARCHIE (Alpha) are now exchanging data and handshakes on my LAN at home without a need for TCP/IP. Likewise, my two test VAX virtual machines, VULPES and CANIS, are doing the same on the library LAN. The next challenge? Get the native Linux host to speak DECnet to one of them, ultimately a virtual VAX hosted on the same physical hardware. Who needs video games when there's this kind of pointless challenge available?
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no subject
Date: 2011-06-23 01:38 pm (UTC)I do believe you mean the lowest 16 bits.
no subject
Date: 2011-06-23 02:10 pm (UTC)Technically, the MAC address substitution is only needed for Phase IV compatibility. DECnet Plus no longer requires funky MAC addresses, but I'm running in Phase IV compatibility mode since I plan to add a PDP-11 node eventually. I don't think RSX ever got as far as DECnet Plus.
no subject
Date: 2011-06-24 01:04 am (UTC)no subject
Date: 2011-06-24 01:14 am (UTC)At the library I'm even safer, since we're behind a good quality dedicated firewall box. Plus we're talking about VMS here, which has been rated by hackers as so tough to crack it isn't worth the trouble. ;p