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DECnet over TCP/IP FAQs

What is DECnet over TCP/IP ?

DECnet over TCP/IP provides a means for DECnet applications to use TCP/IP as a network service rather than the traditional DECnet network service.

It allows the coexistence of DECnet and TCP/IP applications in your network , so that:

  • You can use older DECnet applications as is — no rewriting or re-engineering is needed to support a new network stack.
  • You can write new IP applications for
    e-business and the Internet.
  • You can maintain a single network backbone for cost savings and ease of network management.

DECnet over TCP/IP is based on standards defined in the following RFCs:

  • RFC 1006 - OSI Applications over TCP/IP
  • RFC 1859 - DECnet over TCP/IP
  • RFC 2126 - OSI and DECnet Applications over IPv4 and IPv6

Q: Who can benefit ?

A: Anyone running DECnet applications can take advantage of DECnet over TCP/IP. This includes just about any installation running OpenVMS.

Q: What are the benefits ?

A: DECnet over TCP/IP allows you to balance the demands of existing application users with the pressure to reduce costs by simplifying networking infrastructures.

  • A single network backbone, transmitting multiple network protocols (including NSP, OSI, and TCP) can provide cost savings and simplify network management.
  • DECnet over TCP/IP enables the coexistence of both DECnet and TCP/IP applications on systems connected by a single network backbone

DECnet over TCP/IP makes it possible to combine separate DECnet networks/LANs without renumbering the network nodes. For example, if two companies merge, and both companies have systems with the same node addresses (e.g., Company A has nodes 10.1 through 10.5, and Company B has nodes 10.1 through 10.10), an IP link between the two ensures that the node addresses are unique to the LAN, no costly (and confusing) re-addressing of the nodes is required.

DECnet over TCP/IP offers protection from random intrusions from Internet users. [TCP/IP based intranets need to actively secure the intranet from intrusions. DECnet implements security of the system you are connecting to: TCP/IP security varies by application (e.g., telnet, ftp, etc.)]

Q: Doesn't it require extra network resources ?

A: DECnet over TCP/IP is not just another tunnel or gateway between one protocol and another. Unlike tunnels, there is no duplication of function between the upper layer applications and the lower TCP and IP layers. When using DECnet over TCP/IP, the flow-control and error-recovery mechanisms are those of TCP and underlying IP. As a consequence, there is no inherent performance overhead with running DECnet over TCP/IP, unlike that which is found in tunneling solutions.

Equally important, DECnet over TCP/IP does not define a gateway between the DECnet and TCP/IP worlds. Systems running DECnet over TCP/IP are still DECnet systems ; they just use TCP/IP (along with other protocols) for DECnet communications, while not interfering with "pure" TCP/IP communication from TCP/IP applications on the same systems.

Q: What software do I need? What does it cost?

A: You likely already have installed the software that you need. DECnet over TCP/IP requires that you have a supported version of DECnet-Plus for OpenVMS and a supported version of an industry standard TCP/IP stack, like Compaq TCP/IP Services for OpenVMS. Licenses for both DECnet-Plus for OpenVMS and Compaq's TCP/IP Services for OpenVMS are included in Compaq's Enterprise Integration Package (EIP), which ships with Compaq OpenVMS AlphaServer systems. The products ship on Compaq's Layered Product Consolidated Distribution and also with the OpenVMS Operating System CD.

There are no new/additional costs, no new product licenses or media to purchase or install.

Q: How do I use DECnet over TCP/IP?

A: In order to use DECnet over TCP/IP, you must have installed DECnet-Plus and TCP/IP Services for OpenVMS. In addition, you must enable the PWIP driver as part of the TCP/IP Configuration. Product specific installation instructions are in the appropriate product documentation.

The decision to use DECnet or IP as the transport is based on the remote node address supplied either by the application or the user. You can force a DECnet connection if you supply a DECnet node address or a DECnet fullname; you can force a TCP/IP connection if you supply an IP node address or TCP/IP fullname.

For example, the following will result in using the DECnet transport


The following will result in using the TCP/IP transport


Note that in both cases you are using the DECnet "SET HOST" command.

If you (or the DECnet application) uses a DECnet synonym (also known as an alias and DECnet short name), DECnet session control will select the transport based on how the network manager configured the system. For example, SET HOST NODE1 will force a name to address lookup in DECnet session control. If the lookup returns a DECnet address, the DECnet transport will be used; if the lookup returns an IP address, the TCP/IP transport will be used.

Details on how to configure name resolution in DECnet session control are described in the DECnet-Plus Network Management documentation.

Q: Where can I find out more about DECnet over TCP/IP

A: Go to the the following online resources:

» DECnet-Plus for OpenVMS Applications Installation and Advanced Configuration Manual
» DECnet-Plus for OpenVMS Network Management
» DECnet-Plus Planning Guide
» TCP/IP Services for OpenVMS Installation Guide