DECnet-Plus
Planning Guide
Previous
| Contents
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):
- Create the new backtranslation directories, as needed. Use
decnet_register.
- 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.
- 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.
- 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.
- 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
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.
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:
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
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:
- 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.
- The NSAP node ID represents the Phase IV area and ID. Construct it
as follows:
- Convert the Phase IV area and ID to a single decimal value, using:
(area* 1024) + ID
- 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.
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:
- 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.
- Swap the first and the last pairs of digits, and convert the value
to decimal.
- 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.
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.
4.7 How to Obtain a Unique IDP and PreDSP
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.
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.
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.
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.
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:
The IDI value is based on CCITT Recommendation F.69 and is created from
a Telex number that has been assigned to your company or organization.
The parts of this IDI are:
- 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:
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:
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.
Previous
| Next
| Contents
| [Home]
| [Comments]
| [Ordering info]
| [Help]
PLAN_PROFILE_005.HTML
OSSG Documentation
2-DEC-1996 12:32:10.86
Copyright © Digital Equipment Corporation 1996. All Rights Reserved.
Legal