As per Relevance of the word addresses, we have this rfc below:
Network Working Group L.
Request for Comments: 1236 P.
June 1991
IP to X.121 Address Mapping for
Status of this
This memo defines a standard way of converting IP addresses to
X.121 addresses and is the recommended standard for use on
Internet, specifically for the Defense Data Network (DDN). This
provides information for the Internet community. It does not
an Internet standard. Distribution of this memo is unlimited
1.
The Defense Communication Agency (DCA) has stated that "DDN
a standard for mapping Class A addresses to X.121 addresses."
Additionally DCA has stated that Class B and C IP to X.121
mapping "standards are the responsibility of the administration
the Class B or C network in question". Therefore, there is
defined single standard way of converting Class B and Class C
addresses to X.121 addresses
This is an important issue because currently there is no way
administrators to define IP to X.121 address mapping. Without
single standard, in a multi-vendor network environment, there is
assurance that devices using IP and DDN X.25 will communicate
each other
The IP to X.121 address mapping of Class B and Class C IP
shall be implemented as described below. This translation method
a direct expansion of the algorithm described in the "MIL-STD: X.25,
DDN X.25 Host Interface Specification" [1]. The translation
described below is TOTALLY independent of IP subnetting and of
masking that may be used in support of IP subnetting
2.
All Internet hosts are assigned a four octet (32 bit)
composed of a network field and a local address field also known
the REST field [2] (see Figure 1 thru 3). Two basic forms
addresses are provided: (1) Physical addresses, correspond to
node number and DCE port number of the node to which the DTE
connected. (2) Logical addresses, are mapped transparently by
software into a corresponding physical network address
Morales & Hasse [Page 1]
RFC 1236 IP to X.121 Address Mapping for DDN June 1991
To provide flexibility, Internet addresses are divided into 3
classes: Class A, Class B, and Class C. These classes allow for
large number of small and medium sized networks. The
addresses used within the Internet in Class A, B, and C networks
divided between Research, Defense, Government, (Non-Defense)
Commercial uses
As described in the MIL-STD: X25, an IP address consists of
ASCII text string representation of four decimal numbers separated
periods, corresponding to the four octets of a thirty-two
Internet address. The four decimal numbers are referred to in
memo as network (n), host (h), logical address (l), and
Message Processor (IMP) or Packet Switch Node (PSN) (i). Thus,
Internet address maybe represented as "n.h.l.i" (Class A), "n.n.h.i
(Class B), or "n.n.n.hi" (Class C), depending on the Internet
class. Each of these four numbers will have either one, two,
three decimal digits and will never have a value greater than 255.
For example, in the Class A IP address "26.9.0.122", n=26 h=9, l=0,
and i=122.
The different classes of Internet addresses [3] are
below
Class A
The highest-order bit is set to 0.
7-bits define the network number
24-bits define the local address
This allows up to 126 class A networks
Networks 0 and 127 are reserved
| n | h | l | i |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| NETWORK | Local Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7 Bits 24 Bits (REST Field
Figure 1
Class B
The two highest-order bits are set to 1-0.
14-bits define the network number
16-bits define the local address
This allows up to 16,384 class B networks
Morales & Hasse [Page 2]
RFC 1236 IP to X.121 Address Mapping for DDN June 1991
| n | n | h | i |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 0| NETWORK | Local Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
14 Bits 16 Bits (REST Field
Figure 2
Class C
The three highest-order bits are set to 1-1-0.
21-bits define the network number
8-bits define the local address
This allows up to 2,097,152 class C
| n | n | n | h | i |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 0| NETWORK | Local Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
21 Bits 8 Bits (REST Field
Figure 3
The fourth type of address, class D, is used as a multicast address
The four highest-order bits are set to 1-1-1-0. Note: No
are allowed with the four highest-order bits set to 1-1-1-1.
addresses, called "class E", are reserved
The "MIL-STD: X.25" states "All DDN addresses are either twelve
fourteen BCD (binary-coded decimal) digits in length.". The last
digits are referred to as the Sub-Address and are not used on
DDN. The Sub-Address is carried across the network
modification. Its presence is optional. Therefore, a DTE
generate EITHER a twelve or fourteen BCD X.121 address, but
accept both twelve and fourteen BCD X.121 addresses
3. Standard IP to X.121 Address
This section describes the algorithm that should be used to
IP addresses to X.121 addresses [1]. You will note that "h"
always listed as greater than or less than the number 64.
number is used to differentiate between PSN physical and logical
port addresses. Note that at the time of this writing, the DDN
not make use of the PSN's logical addressing feature, which
hosts to be addressed independently of their physical point
attachment to the network
Morales & Hasse [Page 3]
RFC 1236 IP to X.121 Address Mapping for DDN June 1991
3.1 Derivation of DDN X.25
To convert a Class A IP address to a DDN X.25 address
3.1.1 If the host field (h) is less than 64 (h < 64),
the address corresponds to the following DDN X.25
physical address
ZZZZ F III HH ZZ (SS
where
ZZZZ = 0000
F = 0 because the address is a physical address
III is a three decimal digit representation of "i",
right-adjusted and padded with leading zeros if required
HH is a two decimal digit representation of h", right-
and padded with leading zeros if required
ZZ = 00 is optional
(SS) is an optional Sub-Address field which is ignored in the DDN
This field is either left out or filled with zeros
The address 26.9.0.122 corresponds to the DDN X.25 physical
000001220900.
3.1.2. If the host field (h) is greater than or equal
64 (h >= 64), the address corresponds to the
DDN X.25 physical address
ZZZZ F RRRRR ZZ (SS
where
ZZZZ = 0000
F = 1 because the address is a logical address
RRRRR is a five decimal digit representation of the result "r"
the
r = h * 256 +
(note that the decimal representation of "r" will always require
Morales & Hasse [Page 4]
RFC 1236 IP to X.121 Address Mapping for DDN June 1991
digits
ZZ = 00
(SS) is optional
The address 26.83.0.207 corresponds to the DDN X.25 logical
000012145500.
3.2. For Class B IP addresses the "h" and "i" fields will
consist of 8 bits each taken from the REST field of the
address. The mapping follows the same rules as in 3.1.
3.3. For Class C IP addresses the "h" and "i" fields will
consist of 4 bits each taken from the REST field of the
address. The mapping follows the same rules as in 3.1.
4.
The following are examples of IP to X.121 address mappings for
A, Class B, and Class C IP addresses
4.1 Class
The mapping of X.121 address for Class A networks
for h < 64
example: 26.29.0.122 format: n.h.l.
ZZZZ F III HH ZZ (SS
X.121 address = 0000 0 122 29 00 00
for h > or = 64
example: 26.80.0.122 format: n.h.l.
ZZZZ F RRRRR ZZ (SS
X.121 address = 0000 1 20602 00 00
where R = H * 256 +
4.2 Class
The mapping of X.121 address for Class B networks
Morales & Hasse [Page 5]
RFC 1236 IP to X.121 Address Mapping for DDN June 1991
for h < 64
example: 137.80.1.5 format: n.n.h.
ZZZZ F III HH ZZ (SS
X.121 address = 0000 0 005 01 00 00
for h > or = 64
example: 137.80.75.2 format: n.n.h.
ZZZZ 1 RRRRR ZZ (SS
X.121 address = 0000 1 19202 00 00
where R = H * 256 +
4.3 Class
The mapping of X.121 address for Class C networks
for h < 64
example: 192.33.50.19 format: n.n.n.
H
n.n.n.0001 0011
1 3
Subnet 1
Subhost 3
ZZZZ F III HH ZZ (SS
X.121 address = 0000 0 003 01 00 00
NOTE: The mapping of X.121 address for Class C networks for h > 64
is not applicable since the "h" field can never exceed 15.
5.
[1] MIL-STD: X.25 "Defense Data Network X.25 Host
Specification", Defence Communications Agency, BBN
Corporation, 1983 December, Volume 1 of the "DDN
Handbook" (NIC 50004). Also available online at the DDN NIC
NETINFO:X.25.DOC
[2] MIL-STD: 1777 "Internet Protocol", 1983 August, Volume 1 of
"DDN Protocol Handbook" (NIC 50004).
Morales & Hasse [Page 6]
RFC 1236 IP to X.121 Address Mapping for DDN June 1991
[3] Kirkpatrick, S., M. Stahl, and M. Recker, "Internet Numbers",
1166, DDN NIC, July 1990.
(Unless otherwise indicated, copies of federal and
specifications, standards, and handbooks are available from
Naval Publications and Forms Center, (ATTN: NPODS), 5801
Avenue, Philadelphia, PA 19120-5099.)
6. Security
Security issues are not discussed in this memo
7. Authors'
Luis F. Morales, Jr
ASQB-SEP-
Ft. Huachuca, AZ 85613-5300
Phone: (602) 533-2873
EMail: lmorales@huachuca-emh8.army.
Phillip R.
ASQB-SEP-
Ft. Huachuca, AZ 85613-5300
Phone: (602) 533-2873
EMail: phasse@huachuca-emh8.army.
Morales & Hasse [Page 7]
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