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Planning Guide

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3.3.4 Becoming Familiar with NCL Commands, Network Management Modules, and Network Management Tasks

Use NCL to manage DECnet-Plus software by specifying entity values. You can use NCL commands to:

  • Create and delete entities
  • Enable an entity, which starts the corresponding software module's service
  • Disable an entity, which halts the corresponding software module's service
  • Modify attributes, or characteristics, of an entity
  • Display attributes of an entity

NCL also provides module-specific functions, for example, loopback testing within the Modem Connect module.

In addition to its entity-related functions, NCL provides control functions such as:

  • Aborting NCL operations
  • Establishing defaults for NCL operations

You can execute NCL commands:

  • Interactively at the NCL prompt
  • In command files
  • In initialization scripts
    Initialization scripts are part of the configuration procedure of DECnet-Plus for OpenVMS, DECnet-Plus for DIGITAL UNIX, and other DECnet-Plus products, for example, Phase V router systems.
  • Using the graphical user interface for network management of Phase V nodes.
    sys$system:net$mgmt.exe (for OpenVMS) or
    /usr/sbin/dna_mgmt (for UNIX)
    Choose Default Actions from the Options pull-down menu to display the NCL commands performed on your behalf by the application.

Table 3-4 lists some network management tasks and the related network management entities that you set or modify using NCL commands to perform these tasks. You can use this table during transition to help you learn the modules and entities associated with specific network management tasks. (A complete version of this table also appears in your network management guide.)


All required modules are enabled and all required entities are set during initial configurations, either automatically or by you. Use interactive NCL commands to change initial settings.

Table 3-4 Management Tasks and Related Network Management Modules
Task Module Entities
Enable or disable the system for networking Node node
Manage modem connections Modem Connect modem connect, call control port, data port, line, template
Manage CSMA-CD connections CSMA-CD csma-cd, port, station
Manage synchronous and asynchronous DIGITAL Data Communications Message Protocol (DDCMP) connections DDCMP (DIGITAL UNIX only) ddcmp, link, link logical station, port
Manage synchronous High-level Data Link Control (HDLC) connections HDLC (DIGITAL UNIX only) hdlc, link, link logical station, port
Manage X.25 level 2 protocol to exchange frames between a DTE and a DCE LAPB lapb, link, port
Manage X.25 level 2 for communications over a LAN LLC2 llc2, port, sap, sap link
Downline load and upline dump communications servers such as DEC WANrouter systems MOP mop, circuit, circuit operation, circuit station, client
Manage transport between DECnet-Plus nodes and between DECnet-Plus nodes and multivendor OSI systems OSI transport osi transport, application, local nsap, local nsap remote nsap, port, template
Manage transport between DECnet-Plus nodes and between DECnet-Plus nodes and Phase IV nodes NSP nsp, local nsap, local nsap remote nsap, port
Manage proxies, applications, and processes using the network Session Control session control, application, local node synonym, port, tower maintenance, transport service
Invoke loopback tests between applications on two nodes Loopback Application loopback application
Log events about network operations Event Dispatcher event dispatcher, outbound stream, relay, relay logging, sink, sink inbound stream

3.4 Optional Tasks

Some management tasks related to the transition are required only if your network operations need them:

  • If your initial use of the Local namespace is part of the transition strategy, move to a distributed namespace when you have completed planning for a distributed namespace. For complete information about this procedure, see your network management guide.
  • Set a consistent network buffer size, if you want to avoid the possible dropping of packets by Phase IV routers. For background information and instructions, see Section 3.4.1.
  • If necessary, change your IDP and preDSP. For efficiency, you might choose to make the transition, perhaps with only some of your nodes, using the default IDP. This IDP is not usable for public networks; therefore, a later transition task in this situation is changing your IDP and preDSP to a real one obtained at the appropriate authorized registration agent. For information about registration agents, see Section 4.7. For instructions on making this change, see Section 3.4.2.
  • Choose your main network management tool. An alternative to NCL is POLYCENTER Framework software, a separately orderable product.

3.4.1 Adjusting Buffer Sizes During Transition

In DECnet-Plus, the Transport layer segments and reassembles user messages to a size acceptable to the Routing layer on that system. This method differs from the Phase IV method, in which the Transport layer segments and reassembles user messages to a size appropriate to the complete path over which packets must pass.

DECnet-Plus routing has an additional segmentation capability: if a packet is in the ISO 8473 packet format (the format used between DECnet-Plus systems), a DECnet-Plus router can segment it to fit the data-link size. The Routing layer of the destination system reassembles the segments before delivering the packet to the Transport layer. In contrast, a Phase IV router cannot segment packets to fit the data-link size. When forwarding a packet, a Phase IV router drops the packet if it is too large for the specific data link being used.

For a network in the transition, decide whether to:

  • Establish a consistent buffer size throughout the network or,
  • Accept that some packets will be discarded because they are too large for the data link being used.

To set a consistent network buffer size, use one of the following:

  • On all DECnet-Plus systems, accept the default value of 570 for the routing characteristic segment buffer size. Accepting the default for this routing characteristic on DECnet-Plus systems ensures that they will not send packets larger than any Phase IV data link can handle.
  • On all Phase IV routers, set the parameters executor buffer size and line buffer size to a value greater than or equal to the DECnet-Plus segment buffer size. Setting these parameters ensures that Phase IV routers will be able to forward packets that DECnet-Plus systems send.
  • On all Phase IV systems, set the parameter segment buffer size to less than or equal to the smallest data-link block size. As a result, these systems will not create packets that are too big for the data-link size.

3.4.2 Changing the Network's IDP and preDSP

To change the IDP and preDSP of a network, follow these steps (waiting at least 24 hours between each step):

  1. Create the new backtranslation directories, as needed. Use decnet_register.
  2. Add the new IDP to the routers, using NCL or the appropriate router configuration program. DECnet-Plus nodes automatically learn the new IDP from the routers and update their own entries in the namespace.
  3. Add the new IDP to the information stored in the namespace, using decnet_register. Do not change the local area values.
    This updates nodename entries that do not already have the new IDP.
  4. Remove the old IDP from the routers, using NCL or the appropriate router configuration program. DECnet-Plus nodes automatically learn that the old IDP is no longer in use and update their own entries in the namespace.
  5. Remove the old IDP from the information stored in the namespace, using decnet_register. This updates any node-name entries that have not already had the old IDP removed.

Chapter 4
Creating NSAP Addresses

This chapter discusses the format of NSAP addresses for DECnet-Plus systems and describes how to get unique identification for your DECnet Phase V network. You need this information to:

  • Plan for and complete the transition to DECnet-Plus
  • Design or create a namespace
  • Register DECnet-Plus systems in the namespace
  • Configure DECnet-Plus systems for communications

The DECnet Phase V addressing scheme for DECnet-Plus nodes complies with the ISO 8348 Addendum 2 addressing standard. This scheme uses the concepts of global addressing, addressing authorities, and addressing domains. Global network addressing is an ISO scheme designed to provide unique network addresses throughout the world.

A global network address is called a network service access point (NSAP). Because it is used to determine the destination node for all packets, the NSAP must be unique for each node in a network.

For more information about addressing and service access points (SAPs), refer to Chapter 3 of the DECnet-Plus for OpenVMS Introduction and User's Guide.<>

Some NSAP field values are assigned by an allocation authority, and some you assign yourself for your organization. Every NSAP has two primary fields:

  • Initial domain part (IDP), which consists of two subfields
  • Domain-specific part (DSP), which consists of four subfields

Figure 4-1 shows the parts of an NSAP and network entity title (NET). To compare these parts with Phase IV addresses, see Table 1-1.

Figure 4-1 Parts of an NSAP

4.1 IDP Values

The IDP helps ensure that NSAP values are globally unique. For this reason, IDP values are assigned by recognized authorities or are based on another value (such as a Telex number) that has already been assigned by some authority.

The IDP has two fields:

  • Authority and format identifier (AFI)
    This field identifies the authority that allocated the globally unique IDP.
    The AFI value always consists of two decimal digits (from 0 to 9). Table 4-1 lists the recognized values and the corresponding allocation authorities.
    An AFI value of 49 indicates a private network, one that is not interconnected with other OSI networks and, therefore, does not need a globally unique IDP.
    Table 4-1 shows the NSAP field lengths for each AFI.

    Table 4-1 Information for Building Unique NSAPs
    Allocation Authority AFI Value Maximum Digits in IDI Use AFI if the Leading Digit of the IDI is: Maximum Digits in preDSP
    Private 49 0 (none) N/A 20
    ISO DCC (single-country organizations) 39 3 (exact) N/A 16
    ISO 6523-ICD (international organizations) 47 4 (exact) N/A 16
    X.121 (X.25 address) 37
    14 (maximum) nonzero
    F.69 (Telex number) 41
    8 (maximum) nonzero
    E.163 (telephone number) 43
    12 (maximum) nonzero
    E.164 (ISDN number) 45
    15 (maximum) nonzero

  • Initial domain identifier (IDI)
    This field, combined with the AFI, makes the IDP globally unique for the allocating authority. Depending on the allocation authority identified in the AFI, the IDI value can be explicitly assigned by the authority, or it can be based on some other value that has already been assigned by that authority.
    The IDI value consists of zero or more decimal digits (from 0 to 9). The actual number of digits depends on the AFI. Some AFIs specify fixed-length IDIs, where you must enter all the digits in the IDI. Other AFIs specify variable-length IDIs, where you can enter up to the specified number of digits. Table 4-1 gives the IDI lengths for each AFI.
    If you are using the private AFI (49), do not specify an IDI. AFI 49 indicates a private network not interconnected with other OSI networks.

4.2 DSP Values

The DSP provides unique addresses within a specific IDP value. Different routing architectures might format and use the DSP in different ways. The format used by DECnet-Plus IS-IS, based on OSI IS-IS (ISO 10589), divides the DSP into four fields:

  • Prefix to the DSP (preDSP)
    Also called the high-order part of the DSP (HO-DSP), the format of this field is not defined by DECnet-Plus. If you assign a value to this field, it becomes part of the area, in conjunction with the IDP and local area values, and identifies the node's location for level 2 routing. If nodes have the same IDP and local area values, but different preDSP values, the nodes are in different routing areas.
    The preDSP value is zero or more hexadecimal digits (from 0 to F). The actual number of digits you can enter depends on the AFI. Table 4-1 gives the preDSP sizes appropriate for each AFI.
    The American National Standards Institute (ANSI) is the ISO DCC allocation authority in the United States. For NSAPs with AFI 39, allocated by the ISO DCC, and AFI 47, allocated by ISO 6523-ICD, the allocating authorities may assign an additional value for you to enter into the preDSP field. The reason for this additional value is that they have available only a limited number of IDIs, and they may give the same IDI value to different organizations. When this occurs, the preDSP value ensures global uniqueness.
    Allocation authorities other than ANSI may format the preDSP in other ways. DIGITAL recommends that you do not assign a value to the preDSP field when you use AFIs other than 39 and 47.
    ANSI formats the preDSP into the following subfields:
    • DSP Format Identifier (DFI)
      The value of this field is allocated by ANSI and consists of two hexadecimal digits. It indicates the format used for the rest of the high-order DSP, which is DFI-ORG-RES-RD.
    • Organization ID (ORG)
      The value of this field is allocated by ANSI and consists of six hexadecimal digits. This value is different for every organization and ensures global uniqueness.

    • Reserved (RES)
      The value of this field is allocated by ANSI and consists of four hexadecimal digits. This is a reserved field, whose value must always be zero.
    • Routing Domain (RD)
      The value of this field is allocated by each individual organization and consists of four hexadecimal digits. This field is used to separate an organization's network into multiple routing domains. It is defined so that routing domains can be identified uniquely by intermediate systems using a single short address prefix, without the necessity of listing multiple address prefixes, one for each local area within that routing domain. If your network needs only one routing domain, DIGITAL recommends that you use the value 0000.
  • Local area (LocArea)
    This value represents the local area within the routing domain (the node's local network area). Use the LocArea value, with the IDP and preDSP values, to identify the node's location for level 2 routing.
    This value is used as the next four digits (two octets) in the DSP. The local area value is four hexadecimal digits (from 0 to F). Values 00-01 to 00-3F are reserved for use as Phase IV-compatible area numbers for areas 1 to 63.
  • Node ID
    This part of the DSP identifies a node within an area. It represents the node ID within the local area. Use it to identify the node for level 1 routing purposes.
    Use the node ID value as the next 12 digits (6 octets) in the DSP. This value is 12 hexadecimal digits (from 0 to F). Node IDs that range from AA-00-04-00-00-00 to AA-00-04-00-FF-FF are reserved for use as Phase IV-compatible node IDs (1.1 to 63.1023).
  • Selector (SEL)
    This part of the DSP indicates the transport protocol you want to use. The selector value consists of two hexadecimal digits (from 0 to F). This value is used as the next two digits (one octet) in the DSP. DECnet-Plus uses these SEL values:
    • 20 (for NSAP specifying NSP transport)
    • 21 (for NSAP specifying OSI transport)
    • 00 (for an NET)

4.3 NSAP Entry and Display Formats

Enter an NSAP using either of two standard formats, DNA format or OSI format. DNA format consists of:


OSI format consists of:



aa is the AFI value in decimal
ii... is the IDI value in decimal
pp... is the preDSP value in hexadecimal
ll... is the local area value in hexadecimal
nn... is the node ID value in hexadecimal
ss is the selector value in hexadecimal

DECnet-Plus always displays NSAPs in DNA format because this format separates the various fields, making the NSAP easier to read. The preDSP, local area, and node ID values are punctuated with hyphens after every two digits.

When you enter an NSAP using DNA format:

  • You can type hyphens anywhere.
  • You can omit hyphens.
  • If the local area or node ID fields start with zeros, you can omit them.
  • You cannot omit leading zeros for the IDI and preDSP values. Leading zeros in these fields affect the value of the NSAP when it is used in routing messages.

When you enter an NSAP using OSI format, you must always enter the proper number of digits because there is no other way to indicate where one field ends and the next starts, except between the IDP and DSP. The following examples show NSAPs in both formats.

NSAP with an IDP with the private AFI:

DNA format: 49::00-01:12-34-56-78-9A-BC:21

OSI format: 49+0001123456789ABC21

NSAP with an IDP with an allocated AFI and IDI:

DNA format: 41:23456789:A5:08-00-2B-19-0E-6C:20

OSI format: 4123456789+00A508002B190E6C20

If an NSAP has an unrecognized AFI or does not have the correct number of digits in the IDP or DSP, it is displayed in binary format. This format represents the value of the NSAP as a string of hexadecimal digits, as follows:


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