IP to X.121 address mapping for DDN

Status of this Memo This memo defines a standard way of converting IP addresses to CCITT X.121 addresses and is the recommended standard for use on the Internet, specifically for the Defense Data Network (DDN). This memo provides information for the Internet community. It does not specify an Internet standard. Distribution of this memo is unlimited. 1. Overview The Defense Communication Agency (DCA) has stated that "DDN specifies a standard for mapping Class A addresses to X.121 addresses." Additionally DCA has stated that Class B and C IP to X.121 address mapping "standards are the responsibility of the administration of the Class B or C network in question". Therefore, there is NO defined single standard way of converting Class B and Class C IP addresses to X.121 addresses. This is an important issue because currently there is no way for administrators to define IP to X.121 address mapping. Without a single standard, in a multi-vendor network environment, there is no assurance that devices using IP and DDN X.25 will communicate with each other. The IP to X.121 address mapping of Class B and Class C IP addresses shall be implemented as described below. This translation method is a direct expansion of the algorithm described in the "MIL-STD: X.25, DDN X.25 Host Interface Specification" [1]. The translation method described below is TOTALLY independent of IP subnetting and of any masking that may be used in support of IP subnetting. 2. Background All Internet hosts are assigned a four octet (32 bit) address composed of a network field and a local address field also known as the REST field [2] (see Figure 1 thru 3). Two basic forms of addresses are provided: (1) Physical addresses, correspond to the node number and DCE port number of the node to which the DTE is connected. (2) Logical addresses, are mapped transparently by DCE software into a corresponding physical network address.