DECnet-Plus
Planning Guide

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.

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.

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

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 53	14 (maximum)	nonzero zero	6
  F.69 (Telex number)	41 55	8 (maximum)	nonzero zero	12
  E.163 (telephone number)	43 57	12 (maximum)	nonzero zero	8
  E.164 (ISDN number)	45 59	15 (maximum)	nonzero zero	4

• 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.

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)

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

aa:iii...ii:pp-p...p-pp-ll-ll:nn-nn-nn-nn-nn-nn:ss

OSI format consists of:

aaiii...ii+ppp...pppllllnnnnnnnnnnnnss

where:

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:

/3100A508002B190E6C20

4.4 Converting Phase IV Addresses to NSAPs

To convert a Phase IV address to an NSAP, you encode the Phase IV address into the local area and node ID fields of the NSAP. Fill in all the other NSAP fields in the normal manner.

To encode a Phase IV address into these fields, take the following steps:

1. Make the NSAP local area by using the Phase IV area in hexadecimal.
   For example, Phase IV area 1 becomes NSAP local area 00-01, and Phase IV area 63 becomes NSAP local area 00-3F.
2. The NSAP node ID represents the Phase IV area and ID. Construct it as follows:
   1. Convert the Phase IV area and ID to a single decimal value, using:
      (area* 1024) + ID
   2. Convert the resulting value to a four-digit hexadecimal number, and swap the first and last pairs of hexadecimal digits.
      Use these as the last four digits of the NSAP's node ID field, and prefix them with AA-00-04-00.

For example, with:

• Network IDP 41:45436192:
• Phase IV address 43.258
• The node using NSP transport

then create the NSAP as follows:

IDP and selector    = 41:45436192:local-area:node-id:20     
43 decimal          = 2B    hexadecimal (local area)     
(43 * 1024) + 258   = 44290 decimal     
44290 decimal       = AD02  hexadecimal     
AD02 swapped        = 02AD  hexadecimal (node ID) 

The resulting NSAP is 41:45436192:00-2B:AA-00-04-00-02-AD:20.

4.5 Converting NSAPs to Phase IV Addresses

To convert an NSAP to a Phase IV address, reverse the process described in the previous section.

You get the Phase IV area by converting the local area field from hexadecimal to decimal. If the resulting area value does not fall in the range of 1 to 63 inclusive, the NSAP is an extended address.

Calculate the Phase IV node ID from the node ID field as follows:

1. If the node ID field does not begin with AA-00-04-00, the NSAP does not contain a Phase IV address. If it does begin with this value, extract the last four digits of the node ID field and use them in the following steps.
2. Swap the first and the last pairs of digits, and convert the value to decimal.
3. Calculate the Phase IV area and ID values, using:

   area  = value / 1024 
   id = value - (area * 1024) 
   

   
   If the calculated area value is not equal to the area value obtained from the NSAP's local area field, then the NSAP is an extended address.

For example, with NSAP 37:81076541234:00-19:AA-00-04-00-62-64:21, calculate the Phase IV address by:

19 hexadecimal (from local area)  = 25 decimal     
62-64 (from node ID)              = 6462 hexadecimal     
6462 hexadecimal                  = 25698 decimal     
25698/1024                        = area of 25     
25698 - (25 * 1024)               = id of 98 

The resulting Phase IV address is 25.98.

4.6 Forms of the NSAP Displayed by NCL

Some NCL commands accept and display NETs, area addresses, node IDs, or address prefixes. These values are subsets of a node's full NSAP. This section defines these values and shows how the example NSAP in Figure 4-2 is divided into these values.

Figure 4-2 Example NSAP

Network Entity Title (NET)

The network entity title (NET) is the same as the NSAP, with a selector field of 00. It identifies a node when the specific transport protocol to be used is either unknown or irrelevant. Figure 4-3 illustrates an NET.

Figure 4-3 Example NET

Area Address

An area address consists of the IDP, preDSP, and the local area fields of the NSAP. It identifies a level 2 routing area. Figure 4-4 illustrates an area address.

Figure 4-4 Example Area Address

Node ID

Consists of the node ID field of the NSAP. Identifies a particular node within a level 2 routing area.

Address Prefix

Consists of some leading portion of the NSAP, and can be of any length from zero digits up to the full length of the NSAP. Can be used in a reachable-address table to indicate that packets with a destination NSAP beginning with a specified address prefix are to be routed through a specified circuit.

Phase IV Prefix

Consists of all values up to (but not including) the local area field. Includes the AFI, IDI, and, if used, the preDSP. This value is used by DECnet-Plus when converting between Phase IV addresses and NSAPs.

If your network is to be interconnected with other networks, its NSAP must have a unique IDP and, possibly preDSP, to differentiate it from all other networks. For a unique IDP (and preDSP), you can contact an allocation authority, or you can create your own according to the guidelines in the following sections.

The following sections describe where to obtain an IDI (and preDSP) for a specific AFI.

4.7.1 For a Private Network (AFI 49)

If your network will not be interconnected with other OSI networks, you do not need a unique IDP. Use the AFI 49 with no IDI.

4.7.2 Allocation Authority for Single-Country Organizations (AFI 39)

The IDI value is assigned directly for each country by an authorized registration agent, according to ISO Standard 3166. The registration authority agent in the United States is the American National Standards Institute (ANSI), with offices in New York City.

In this case, the resulting IDP is entered as given by the allocation authority. This IDP might also require the allocation of a value to be placed in the preDSP.

4.7.3 Allocation Authority for International Organizations (AFI 47)

The IDI value is assigned directly for each international organization by an authorized registration agent, according to ISO Standard 6523-ICD.

In this case, the resulting IDP is entered as given by the allocation authority. This IDP might also require the allocation of a value to be placed in the preDSP.

4.7.4 Using an X.25 Data Network Address for the IDI (AFIs 37 and 53)

The IDI value is based on CCITT Recommendation X.121 and is created from a public or private data network address. The parts of this IDI are:

• Data network identification code (DNIC)
  Assigned by the CCITT registration agent in a country; four digits long.
• Private network identification code (PNIC)
  Assigned by the CCITT registration agent or by the public or private data network to which your equipment is connected; three digits long.
• Address within the private network
  The network manager assigns this address for each node. Choose one node's address and use it to create a unique IDI value for your network.
  The node whose X.25 address you choose does not have to be part of the network for which you are creating the IDI. The address serves simply as a unique number that has been assigned to you.

Example:

Company's subnetwork address prefix (DNIC and PNIC)   = 8107654 
Address within company's subnetwork                   = 1234 

Resulting IDP value = 37:81076541234:

4.7.5 Using a Telex Number for the IDI (AFIs 41 and 55)

• Destination code (country or network number), either two or three digits
  See the appropriate CCITT reference for the list of destination codes.
• Local Telex number, six or five digits (depending on the destination code)
  Choose one Telex number and use it to create a unique IDI value for your network. This number serves simply as a unique number that has been assigned to you. When choosing a Telex number, make sure it conforms to CCITT Recommendation F.69.

Example:

Destination code (for Switzerland)  = 45 
Local Telex number                  = 43 61 92 

Resulting IDP value = 41:45436192:

4.7.6 Using a Telephone Number for the IDI (AFIs 43 and 57)

The IDI value is based on CCITT Recommendation E.163 and is created from a public switched telephone network (PSTN) number that has been assigned to your company or organization. The parts of this IDI are:

• World zone number
• Country or geographic area number
• Local number

Consult your local PSTN for the world zone and the country numbers.

Choose one telephone number and use it to create a unique IDI value for your network. This number serves simply as a unique number that has been assigned to you.

Example:

World zone number (for U.S.A.)               = 1 
Geographic area number (for Massachusetts)   = 508 
Local number                                 = 555-1192 

Resulting IDP value = 43:15085551192:

4.7.7 Using an ISDN Number for the IDI (AFIs 45 and 59)

The IDI value is based on CCITT Recommendation E.164 and is created from an integrated services digital network (ISDN) number that has been assigned to your organization. ISDN is a technology offered by the telephone carriers of the world that combines voice and digital network services in one media, allowing for digital data services through a single "wire." The standards that define ISDN are specified by CCITT.

The parts of this IDI are:

• Country code (CC)
  The country code is one to three digits and is administered by CCITT.
• National destination code (NDC)
  For the U.S.A. and Canada, the NDC is the 3-digit area code.
• Subscriber number (SN)
  For the U.S.A. and Canada, the SN is the local telephone number.

The NDC and SN, which together make up the national significant number, are administered within each country, usually by the PTT.

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