IETF 1 January 25, 1993 CLNP for TUBA Internet Draft Expires in 6 months Use of ISO CLNP in TUBA Environments David M. Piscitello Bellcore dave@sabre.bellcore.com Status of this Memo This document is an Internet Draft. Internet Drafts are working documents of the Internet Engineering Task Force (IETF), its Areas, and its Working Groups. Note that other groups may also distribute working documents as Internet Drafts). Internet Drafts are draft documents valid for a maximum of six months. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a "working draft" or "work in progress." Please check the Internet Draft abstract listing contained in the IETF Shadow Directories (cd internet-drafts) to learn the current status of this or any other Internet Draft. This Internet-Draft specifies a profile of the ISO 8473 Connectionless-mode Network Layer Protocol (CLNP, [1]) for use in conjunction with RFC 1347, TCP/UDP over Bigger Addresses (TUBA, [2]). This draft document will be submitted to the RFC editor as a protocol specification. Distribution of this memo is unlimited. Please send comments to dave@sabre.bellcore.com. Abstract This document describes the use of CLNP to provide the lower- level service expected by Transmission Control Protocol (TCP, [3]) and User Datagram Protocol (UDP, [4]). CLNP provides essentially the same datagram service as Internet Protocol (IP, [5]), but offers a means of conveying bigger network addresses (with additional structure, to aid routing). While the protocols offer nearly the same services, IP and CLNP are not identical. This document describes a means of preserving the semantics of IP information that is absent from CLNP while preserving consistency between the use of CLNP in Internet and OSI environments. This maximizes the use of already-deployed CLNP implementations. Acknowledgments IETF 2 Internet Draft CLNP for TUBA September 3, 1992 Many thanks to Ross Callon of Digital Equipment and Dave Katz of Cisco Systems for their lightning-quick replies to my frequent requests for sanity-checks. Thanks also to the members of the tuba mailing list, who commented on an earlier draft of this paper. Conventions The following language conventions are used in the items of specification in this document: o+ Must, Shall, or Mandatory -- the item is an absolute requirement of the specification. o+ Should or Recommended -- the item should generally be followed for all but exceptional circumstances. o+ May or Optional -- the item is truly optional and may be followed or ignored according to the needs of the implementor. 1. Terminology To the extent possible, this document is written in the language of the Internet. For example, packet is used rather than "protocol data unit", and "fragment" is used rather than "segment". There are some terms that carry over from OSI; these are, for the most part, used so that cross-reference between this document and RFC994 or ISO 8473 is not entirely painful. OSI acronyms are for the most part avoided. 2. Introduction The goal of this specification is to allow compatible and interoperable implementations to encapsulate TCP and UDP packets in CLNP data units. It is assumed that readers are familiar with RFC 791 and, to a lesser extent, RFC 994 and ISO 8473. This document is compatible with (although more restrictive than) ISO 8473; specifically, the order, semantics, and processing of CLNP header fields is consistent between this and ISO 8473. However, it is intended that this document be able to stand on its own without reference to ISO 8473, at least with respect to implementing CLNP to provide the lower-level service expected by TCP and UDP. [Editor's Note: RFC 994 contains the Draft International Standard version of ISO CLNP [6]; while this is not the final version of the ISO protocol specification, it should provide sufficient background for the purpose of understanding the relationship of CLNP to IP, and the means whereby IP information is to be encoded IETF 3 September 3, 1992 CLNP for TUBA Internet Draft in CLNP header fields. More importantly, it's available on- line:-)] 3. Overview of CLNP ISO CLNP is a datagram network protocol. It provides fundamentally the same underlying service to a transport layer as IP. CLNP provides essentially the same maximum datagram size, and for those circumstances where datagrams may need to traverse a network whose maximum packet size is smaller than the size of the datagram, CLNP provides mechanisms for fragmentation (data unit identification, fragment/total length and offset). Like IP, a checksum computed on the CLNP header provides a verification that the information used in processing the CLNP datagram has been transmitted correctly, and a lifetime control mechanism ("Time to Live") imposes a limit on the amount of time a datagram is allowed to remain in the internet system. As is the case in IP, a set of options provides control functions needed or useful in some situations but unnecessary for the most common communications. Errors detected during the processing of a CLNP datagram may be reported using CLNP Error Reports. Table 1 provides a high-level comparison of CLNP to IP: Function | ISO CLNP | DOD IP ------------------------|-----------------------|----------------- Version Identifier | 1 octet | 4 bits Header Length | indicated in octets | in 32-bit words Total Length | 16 bits, in octets | 16 bits, in octets Data Unit Identifier | 16 bits | 16 bits Flags | Fragmentation allowed,| Don't Fragment, | More Fragments | More Fragments, | Suppress Error Reports| Fragment offset | 16 bits, in octets | 13 bits, 8-octet units Lifetime (Time to live) | 500 msec units | 1 sec units Higher Layer Protocol | Selector in address | PROTOcol (assigned #) Header Checksum | 16-bit (Fletcher) | 16-bit Addressing | Variable length | 32-bit fixed Options | Security | Security | Priority | Precedence bits in TOS | Complete Source Route | Strict Source Route | Quality of Service | Type of Service | Partial Source Route | Loose Source Route | Record Route | Record Route | Padding | Padding | | Timestamp Table 1. Comparison of IP to CLNP IETF 4 Internet Draft CLNP for TUBA September 3, 1992 Note that the encoding of options differs between the two protocols, as do the means of higher level protocol identification. Note also that CLNP and IP differ in the way header and fragment lengths are represented, and that the granularity of lifetime control (time-to-live) is finer in CLNP. Some of these differences are not considered "issues", as CLNP provides flexibility in the way that certain options may be specified and encoded (this will facilitate the use and encoding of certain IP options without change in syntax); others, e.g., higher level protocol identification and timestamp, must be accommodated in a transparent manner in this profile for correct operation of TCP and UDP, and continued interoperability with OSI implementations. Section 4 describes how header fields of CLNP must be populated to satisfy the needs of TCP and UDP. CLNP and IP differ in the way in which errors are reported to hosts. In IP environments, the Internet Control Message Protocol (ICMP, [7]) is used to return (error) messages to hosts that originate packets that cannot be processed. An unique message type, the Error Report, is used in CLNP. Table 2 provides a loose comparison of ICMP messages to CLNP Error Reports. CLNP Error Report | ICMP Message --------------------------------|--------------------------------- Reason not specified | <> Protocol Procedure Error | <> Incorrect Checksum | <> PDU Discarded--Congestion | Source Quench (Note 1) Header Syntax Error | Parameter problem Needed to Fragment, could not | Needed to Fragment, Don't Fragment set Incomplete PDU received | <> Duplicate Option | <> Destination Unreachable | Destination Unreachable Destination Unknown | Remote Net/Host Unknown (2) Source Routing Error | Source Route failed Unknown Address in Source Route | Source Route failed(?) Path not acceptable | <> Lifetime expired in transit | Time to live exceeded Reassembly Lifetime Expired | Fragment reassembly time exceeded Unsupported Option | <> Unsupported Protocol Version | Parameter problem Unsupported Security Option | Parameter problem Unsupported Source Route Option | Parameter problem Unsupported Record Route option | Parameter problem Reassembly interference | <> Echo Request/Reply | CLNP Ping, see RFC1139 (3) Redirect | RD packet of ES/IS protocol (4) Table 2. Comparison of CLNP Error Reports to ICMP Messages IETF 5 September 3, 1992 CLNP for TUBA Internet Draft [Editor's Note: <> means I could find not comparable value; it is an open issue whether these error messages may be used in TUBA environments. An analysis of the error reporting of CLNP and ICMP continues.] Note 1: The current use of the source quench is only when packets are discarded, and thus the current use meaning is the same; if a future RFC describes a more robust treatment of the source quench, the applicability of this CLNP Error Report Type should be reconsidered. Note 2: Remote Net Unknown and Remote Host Unknown are defined as sub-options of the ICMP Destination Unreachable message in RFC1122, Host Requirements. Note 3: The long-term option defined in RFC1139 shall be used. This is consistent with the current ISO proposal/addendum [cf]. Note 4: The Redirect packet of the ISO End System to Intermediate System Routing Exchange Protocol (ISO 9542) is used. 4. Proposed Internet Header using CLNP A summary of the contents of the CLNP header, as it is proposed for use in TUBA environments, is illustrated in Figure 1: IETF 6 Internet Draft CLNP for TUBA September 3, 1992 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ........Data Link Header........ | NLP ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Header Length | Version | Lifetime (TTL)|Flags| Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Fragment Length | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Dest Addr Len | Destination Address... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... Destination Address... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... Destination Address... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... Destination Address... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... Destination Address... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PROTO field | Src Addr Len | Source Address... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... Source Address... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... Source Address... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... Source Address... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... Source Address... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... Source Address | Reserved | Data Unit... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ...Identifier | Fragment Offset |Total Length.. | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ... of Packet | Options... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | : : | Options (see Table 1) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Note that each tick mark represents one bit position. Figure 1. CLNP for TUBA The encoding of CLNP fields for use in TUBA environments is as follows. IETF 7 September 3, 1992 CLNP for TUBA Internet Draft 4.1 Network Layer Protocol Identification (NLP ID) This one-octet field identifies this as the ISO 8473 protocol; it must set to binary 1000 0001. 4.2 Header Length Indication (Header Length) Header Length is the length of the CLNP header in octets, and thus points to the beginning of the data. Note that the minimum value for a correct header -- when CLNP is used to convey TCP or UDP -- is 57. This assumes both the source and destination addresses are precisely 20 octets long, including the "protocol" and "protocol/reserved" fields, respectively. (This also assumes that no options are present). The value 255 is reserved. The header length is the same for all fragments of the same (original) CLNP packet. 4.3 Version This one-octet field identifies the version of the protocol; it is set to a binary value 0000 0001. 4.4 Lifetime (TTL) Like the TTL field of IP, this field indicates the maximum time the datagram is allowed to remain in the internet system. If this field contains the value zero, then the datagram must be destroyed. This field is modified in internet header processing. The time is measured in units of 500 milliseconds, but since every module that processes a datagram must decrease the TTL by at least one even if it process the datagram in less than 500 millisecond, the TTL must be thought of only as an upper bound on the time a datagram may exist. The intention is to cause undeliverable datagrams to be discarded, and to bound the maximum CLNP datagram lifetime. [Like IP, the colloquial usage of TTL in CLNP is as a coarse hop-count.] 4.5 Flags Three flags are defined. These occupy bits 0, 1, and 2 of the Flags/Type octet: 0 1 2 +---+---+---+ | F | M | E | | P | F | R | +---+---+---+ The Fragmentation Permitted (FP) flag, when set to a value of one (1) is semantically equivalent to the "may fragment" value of the Don't Fragment field of IP; similarly, when set to zero (0), the Fragmentation Permitted flag is semantically equivalent to the IETF 8 Internet Draft CLNP for TUBA September 3, 1992 "Don't Fragment" value of the Don't Fragment Flag of IP. If the Fragmentation Permitted field has the value O, then the Data Unit Identifier, Fragment Offset, and Total Length fields are not present. The More Fragments flag of CLNP is semantically and syntactically the same as the More Fragments flag of IP; a value of one (1) indicates that more segments/fragments are forthcoming; a value of zero (0) indicates that the last octet of the original packet is present in this segment. The Error Report (ER) flag is used to suppress the generation of an error message by a host/router that detects an error during the processing of a CLNP datagram; a value of one (1) indicates that the host that originated this datagram thinks error reports are useful, and would dearly love to receive one if a host/router finds it necessary to discard its datagram(s). 4.6 Type field The type field distinguishes data CLNP packets from Error Reports; a value of binary 11100 in bits 3-7 of the Flags/Type octet indicates that this is a data packet; a value of binary 00001 (go figure...) indicates that this is an Error Report. 0 1 2 3 4 5 6 7 +---+---+---+---+---+---+---+---+ | flags | 1 | 1 | 1 | 0 | 0 | => Encoding of Type = data packet +---+---+---+---+---+---+---+---+ | flags | 0 | 0 | 0 | 0 | 1 | => Encoding of Type = error report +---+---+---+---+---+---+---+---+ 4.7 Fragment Length Like the Total Length of the IP header, the Fragment length field contains the length in octets of the fragment (i.e., this datagram) including both header and data. [Note: CLNP also has a Total Length field, that contains the length of the original datagram; i.e., the sum of the length of the CLNP header plus the length of the data submitted by the higher level protocol, e.g., TCP or UDP). 4.8 Checksum A checksum on the header only, verified at each host/router that processes the packet; if header fields are changed during processing (e.g., the Lifetime), the checksum is modified. If the checksum is not used, this field must be coded with a value of zero (0). See Appendix A. IETF 9 September 3, 1992 CLNP for TUBA Internet Draft 4.9 Destination Address Length Indicator () This field indicates the length, in octets, of the Destination Address. It must be set to the value 20. 4.10 Destination Address The format of the address encoded in this field is described in a companion addressing document, see [8]; Appendix B briefly identifies the formats under consideration at this time. For compatibility and interoperability with OSI use of CLNP, the initial octet of the Destination Address is assumed to be an Authority and Format Indicator, as defined in ISO 8348 [7]. A destination address must be 20 octets long; the 20th octet must always contain the value of the PROTO field, as defined in IP. The 8-bit PROTO field indicates the next level protocol used in the data portion of the CLNP datagram. The values for various protocols are specified in "Assigned Numbers" [9]. For the PROTO field, the value of zero (0) is reserved. 4.11 Source Address Length Indicator () This field indicates the length, in octets, of the Source Address. It must be set to the value 20. 4.12 Source Address The format of the address encoded in this field is described in a companion addressing document, see [8]. Appendix B briefly identifies the formats under consideration at this time. For compatibility and interoperability with OSI use of CLNP, the initial octet of the Destination Address is assumed to be an Authority and Format Indicator, as defined in ISO 8348 [7]. A destination address must be 20 octets long; the 20th octet must always be reserved. It may be set to the protocol field value on transmission, and shall be ignored on reception. For the 20th octet, the value of zero is reserved. 4.13 Data Unit Identifier Like the Identification field of IP, this 16-bit field is used to distinguish segments of the same (original) packet for the purposes of reassembly. 4.14 Fragment Offset Like the Fragment Offset of IP, this 16-bit is used to identify the relative octet position of the data in this fragment with respect to the start of the data submitted to CLNP; i.e., it indicates where in the original datagram this fragment belongs. IETF 10 Internet Draft CLNP for TUBA September 3, 1992 4.15 Options All CLNP options are of the form , , and . Both the parameter code and length fields are always one octet long; the length parameter value, in octets, is indicated in the parameter length field. The following options are defined for CLNP for TUBA. 4.15.1 _S_e_c_u_r_i_t_y The value of the parameter code field is binary 1100 0101. The length field must be set to the length of a Basic (and Extended) Security IP option(s) as identified in RFC1108 [10], plus 1. Octet 1 of the security parameter value field -- the CLNP Security Format Code -- is set to a binary value 0100 0000, indicating that the remaining octets of the security field contain either the Basic or Basic and Extended Security options as identified in RFC 1108 [10]. This encoding points to the administration of the source address (e.g., ISOC) as the administration of the security option; it is thus distinguished from the globally unique format whose definition is reserved for OSI use. Implementations must examine the PROTO field in the source address; if the value of PROTO indicates the CLNP client is TCP or UDP, the security option described in RFC1108 is used. The formats of the Security option, encoded as a CLNP option, is as follows. The CLNP option will be used to convey the Basic and Extended Security options as sub-options; i.e., the exact encoding of the Basic/Extended Security IP Option is carried in a single CLNP Security Option, with the length of the CLNP Security option reflecting the sum of the lengths of the Basic and Extended Security IP Option. +--------+--------+--------+--------+--------+------//-----+--- |11000100|XXXXXXXX|01000000|10000010|YYYYYYYY| | ... +--------+--------+--------+--------+--------+------//-----+------ CLNP CLNP CLNP BASIC BASIC BASIC OPTION OPTION FORMAT SECURITY OPTION OPTION TYPE LENGTH CODE TYPE LENGTH VALUE (197) (130) ---+------------+------------+----//-------+ ... | 10000101 | 000LLLLL | | -----+------------+------------+----//-------+ EXTENDED EXTENDED EXTENDED OPTION OPTION OPTION VALUE TYPE (133) LENGTH IETF 11 September 3, 1992 CLNP for TUBA Internet Draft The syntax, semantics and processing of the Basic and Extended IP Security Options are defined in RFC1108. 4.15.2 _T_y_p_e__o_f__S_e_r_v_i_c_e The value of the parameter code field must be set to a value of binary 1100 0011 (the CLNP Quality of Service Option Code point). The length field must be set to the length of the type of service field as identified in RFC1349, Type of Service in the Internet Protocol Suite [11], plus 1 (i.e., the value is 2). Octet 1 of the type of service parameter field is set to a binary value 0100 0000, indicating that the remaining octet of the Type Of Service field is to be encoded as described in RFC1349. This encoding points to the administration of the source address (e.g., ISOC) as the administration of the CLNP QOS option; it is thus distinguished from the globally unique QOS format whose definition is reserved for OSI use. Implementations must examine the PROTO field in the source address; if the value of PROTO indicates the CLNP client is TCP or UDP, the TOS described in RFC1349 is used. +-----------+----------+----------+----------+ | 1100 0011 | 00000010 | 01000000 | PPPTTTT0 | +-----------+----------+----------+----------+ CLNP QOS OPTION QOS FORMAT IP TOS TYPE (195) LENGTH CODE OCTET The Type of Service octet consists of three fields: 0 1 2 3 4 5 6 7 +-----+-----+-----+-----+-----+-----+-----+-----+ | PRECEDENCE | TOS | MBZ | +-----+-----+-----+-----+-----+-----+-----+-----+ The first field, labeled "PRECEDENCE" above, is intended to denote the importance or priority of the datagram. The second field, labeled "TOS" above, denotes how the network should make tradeoffs between throughput, delay, reliability, and cost. The last field must be zero ("MBZ"). The processing of the type of service option is defined in RFC1349. The rules for applying TOS in Error and Report messages should correspond to those applied to the corresponding ICMP messages; i.e., error messages must always be sent with the default TOS; request messages may have any correct TOS value, and replies must be sent with the same value in the TOS field as was used in the corresponding request message. IETF 12 Internet Draft CLNP for TUBA September 3, 1992 [Editor's Note: It has been suggested that the IP precedence map directly into a CLNP option, Priority. The feature will be provided irrespective of whether precedence is encoded in the TOS or Priority option.] 4.15.3 _P_a_d_d_i_n_g The padding field is used to lengthen the packet header to a convenient size. The parameter code field must be set to a value of binary 1100 1100. The value of the parameter length field is variable. The parameter value may contain any value. +----------+----------+-----------+ | 11001100 | LLLLLLLL | VVVV VVVV | +----------+----------+-----------+ 4.15.4 _S_o_u_r_c_e__R_o_u_t_i_n_g Like the strict source route option of IP, the Complete Source Route option of CLNP is used to specify the exact and entire route an internet datagram must take. Similarly, the Partial Source Route option of CLNP provides the the equivalent of the loose source route option of IP; i.e., a means for the source of an internet datagram to supply (some) routing information to be used by gateways in forwarding the internet datagram towards its destination. The parameter code for Source Routing is binary 1100 1000. The length of the source routing parameter value is variable. The first octet of the parameter value is a type code, indicating Complete Source Routing (binary 0000 0001) or partial source routing (binary 0000 0000). A complete description of the encoding of the parameter values of this option is to be provided. 4.15.5 _R_e_c_o_r_d__R_o_u_t_e Like the IP record route option, the Record route option of CLNP is used to trace the route a CLNP datagram takes. The parameter code for Record Route is binary 1100 1011. The length of the record route parameter value is variable. A complete description of the parameter value of this option is to be provided. 4.15.6 _T_i_m_e_s_t_a_m_p [Editor's Note: There is no timestamp option in CLNP. We propose to define the option and submit it to ISO; temporarily, we will be most presumptuous and "borrow" a code point from the many that are reserved.] IETF 13 September 3, 1992 CLNP for TUBA Internet Draft This paper proposes that the parameter code value 1110 1110 be used to identify the Timestamp option, and that the syntax and semantics of Timestamp be identical to that defined in IP. The Timestamp Option is defined in RFC 791. It is proposed that the parameter code 1110 1110 be used rather than the option type code 68 to identify the Timestamp option, and that the parameter value convey the option length. Octet 1 of the Timestamp parameter value shall be encoded as the pointer (octet 3 of IP Timestamp); octet 2 of the parameter value shall be encoded as the overflow/format octet (octet 4 of IP Timestamp); the remaining octets shall be used to encode the timestamp list. The size is fixed by the source, and cannot be changed to accommodate additional timestamp information. +--------+--------+--------+--------+ |11101110| length | pointer|oflw|flg| +--------+--------+--------+--------+ | internet address | +--------+--------+--------+--------+ | timestamp | +--------+--------+--------+--------+ | . | . IETF 14 Internet Draft CLNP for TUBA September 3, 1992 5. REFERENCES [1] ISO 8473--International Standards Organization--Data Communications-- Protocol for Providing the Connectionless-mode Network Service [2] Callon, R., TCP/UDP over Bigger Addresses (TUBA), Request for Comments 1347, Network Information Center, SRI International, Menlo Park, CA, May 1992. [3] Postel, J., Transmission ControlProtocol. Request for Comments 793, Network Information Center, SRI International, Menlo Park, CA, 1981 September. [4] RFC768, User Datagram Protocol. Request for Comments 768, Network Information Center, SRI International, Menlo Park, CA [5] Postel, J., Internet Protocol. Request for Comments 791, Network Information Center, SRI International, Menlo Park, CA, 1981 September. [6] RFC994, ISO CLNP, Draft International Standard version. [7] ISO8348--International Standards Organization--Data Communications--OSI Network Layer Addressing [8] RFCiiii, Addressing for the new Internet [9] RFC1340, Reynolds, J., and J. Postel, Assigned Numbers. [10] RFC1108, Kent, S., Security Option for IP. [11] RFC1349, Almquist, P., Type of Service in the Internet Protocol Suite. [12] ISO 6523 -- International Code Designators IETF 15 September 3, 1992 CLNP for TUBA Internet Draft Appendix A. Checksum Algorithms (from ISO 8473) Symbols used in algorithms: c0, c1 variables used in the algorithms i position of octet in header (first octet is i=1) Bi value of octet i in the header n position of first octet of checksum (n=8) L Length of header in octets X Value of octet one of the checksum parameter Y Value of octet two of the checksum parameter Addition is performed in one of the two following modes: o+ modulo 255 arithmetic; o+ eight-bit one's complement arithmetic; The algorithm for Generating the Checksum Parameter Value is as follows: A. Construct the complete header with the value of the checksum parameter field set to zero; i.e., c0 <- c1 <- 0; B. Process each octet of the header sequentially from i=1 to L by: o+ c0 <- c0 + Bi o+ c1 <- c1 + c0 C. Calculate X, Y as follows: o+ X <- (L - 8)(c0 - c1) modulo 255 o+ Y <- (L - 7)(-C0) + c1 D. If X = 0, then X <- 255 E. If Y = 0, then Y <- 255 F. place the values of X and Y in octets 8 and 9 of the header, respectively The algorithm for checking the value of the checksum parameter is as follows: A. If octets 8 and 9 of the header both contain zero, then the checksum calculation has succeeded; else if either but not both of these octets contains the value zero then the checksum is incorrect; otherwise, initialize: c0 <- c1 <- 0 IETF 16 Internet Draft CLNP for TUBA September 3, 1992 B. Process each octet of the header sequentially from i = 1 to L by: o+ c0 <- c0 + Bi o+ c1 <- c1 + c0 C. When all the octets have been processed, if c0 = c1 = 0, then the checksum calculation has succeeded, else it has failed. There is a separate algorithm to adjust the checksum parameter value when a octet has been modified (such as the TTL). Suppose the value in octet k is changed by Z = newvalue - oldvalue. If X and Y denote the checksum values held in octets n and n+1 respectively, then adjust X and Y as follows: If X = 0 and Y = 0 then do nothing, else if X = 0 or Y = 0 then the checksum is incorrect, else: X <- (k - n - 1)Z + X modulo 255 Y <- (n - k)Z + Y modulo 255 If X = 0, then X <- 255; if Y = 0, then Y <- 255. In the example, n = 89; if the octet altered is the TTL (octet 4), then k = 4. For the case where the lifetime is decreased by one unit (Z = -1), the assignment statements for the new values of X and Y in the immediately preceeding algorithm simplify to: X <- X + 5 Modulo 255 Y <- Y - 4 Modulo 255 IETF 17 September 3, 1992 CLNP for TUBA Internet Draft Appendix B. Address formats At least two alternatives for an ISOC network address format have been posted to the TUBA list. In both cases, the actual "bits for routing" are virtually identical; the encoding of the highest level administration -- the Internet Society -- differs because in case 1, the Internet Society applies directly to ISO/CCITT for an authority code-point at the highest branch of the addressing tree. This would be recorded in the OSI Network Layer Addressing Standard, ISO 8438 [ ]. Thus, for case 1, the encoding of a network address is as follows: CASE 1: ISOC obtains an AFI. In this case, the format of the address, left-to-right is: 1 byte Identifies "ISOC" 1 byte Identifies type of address format. Currently assigned value is "service provider". Future values might specify "geographic", "flat", etc.. (note that "flat" would provide a globally unique address which would not be routed by public service providers). if addr type specifies "service provider", rest of address looks like: 2 bytes Identifies country, or continent (for international networks), or "inter-continental network". NOTE: Top-level is included in case, in the future, we have more than 10,000 service providers, and need to route between them hierarchically. 2 bytes Specifies public service provider (regional or backbone) NOTE: So long as there are no more than 10,000 public service providers worldwide, routing between them would be on a "flat" basis, using the first 6 bytes of the address as if it were a flat field. 3 bytes Reserved for future use, as will be specified by the IETF. This is intended for future hierarchical assignment of customer addresses by PSP's (i.e., will be used when there are more than 10,000 customers attached to a single PSP). 2 bytes Identifies the RD which is a customer of a PSP 2 bytes Identifies the area within the routing domain 6 bytes Identifies the host. This is globally unique. 1 byte Identifies higher level protocol running over CLNP. (Uses values from current "assigned numbers" RFC) total: 20 bytes IETF 18 Internet Draft CLNP for TUBA September 3, 1992 In case 2, the ISOC applies for an International Code Designator (ICD) from ISO/CCITT; the ICD's are assigned out of the AFI code-point 47, which says that the two octets that immediately follow the AFI identify an international organization, in this case "ISOC". The ICD code point would be recorded in ISO 6523 [12], International Code Designators. CASE 2: ISOC obtains an ICD. In this case, the format of the address, left-to-right is: 1 byte Identifies "ISO6523-ICD" 2 bytes ICD = "ISOC" 1 byte Identifies type of address format. Currently assigned value is "service provider". Future values might specify "geographic", "flat", etc.. (note that "flat" would provide a globally unique address which would not be routed by public service providers). if addr type specifies "service provider", rest of address looks like: 2 bytes Identifies country, or continent (for international networks), or "inter-continental network". NOTE: Top-level is included in case, in the future, we have more than 10,000 service providers, and need to route between them hierarchically. 2 bytes Specifies public service provider (regional or backbone) NOTE: So long as there are no more than 10,000 public service providers worldwide, routing between them would be on a "flat" basis, using the first 6 bytes of the address as if it were a flat field. 1 byte Reserved for future use, as will be specified by the IETF. This is intended for future hierarchical assignment of customer addresses by PSP's (i.e., will be used when there are more than 10,000 customers attached to a single PSP). 2 bytes Identifies the RD which is a customer of a PSP 2 bytes Identifies the area within the routing domain 6 bytes Identifies the host. This is globally unique. 1 byte Identifies higher level protocol running over CLNP. (Uses values from current "assigned numbers" RFC) total: 20 bytes Note that in both cases 1 and 2, the total length has been fixed at a maximum length of 20 octets; note also that the use of CLNP described in this Internet-draft requires only that the last (20th) octet of the network addresses be reserved to encode the PROTO value from IPv4, and that network addresses eventually used IETF 19 September 3, 1992 CLNP for TUBA Internet Draft be fixed to a maximum length of 20 octets to take advantage of a fixed sized header for more efficient processing (when options are not used). The use of TUBA should not prevent use of any NSAPA format. Some backbone and regional networks currently use addresses that do not conform to the requirement of a fixed length 20 octet address; thus, the following has been proposed to the tuba mailing list: o+ For the long term, addresses must be 20 octets long. o+ The last 7 octets of the address shall consist of a globally meaningful identifier of 6 octets plus a selector field of one octet, which shall use "protocol" values from Assigned Numbers. o+ The high order 13 octets of the address may make use of any valid NSAP address. o+ In the near term, (until (mm/dd/yy)), other address lengths are also permitted, but in all cases the low order seven octets must consists of an ID plus selector. Networks which are currently using shorter NSAPAs are required to be updated by this date. Hosts and routers may be optimized for 20 octet network addresses, but until mm/dd/yy they are required to support shorter addresses. o+ When a system is using CLNP for other protocol suites (in addition to the Internet suite), it is permissible to do either of the following: 1. The addresses used for the other suites may be taken from the same space as addresses used with TUBA. In this case, the selector, representing the last octet of the NSAPA, must use the values from Assigned Numbers (note that there is a value for OSI TP Class 4 defined in Assigned Numbers). 2. The address used for the other suites may be taken from a different space from addresses used with TUBA. In this case, the addresses used for other purposes (e.g., for OSI over CLNP) would be different from the addresses used for running TUBA over CLNP. In this case, a host which is running both Internet applications and OSI applications over CLNP would need at least two different NSAPAs assigned to it. IETF 20 Internet Draft CLNP for TUBA September 3, 1992 Appendix C. Issues 1. Is it useful to mandate in the CLNP for TUBA profile that both the QoS and Priority options be present in every packet? We can define a fixed correspondence of IP ToS to CLNP QoS and IP Precedence to CLNP Priority. It has been suggested that this would make the host changes easier and provide another dimension in which the functionality of the two packet encodings would be isomorphic. 2. Shall we use the AFI = ISOC or ISO 6523-ICD = ISOC form of network addressing? 3. We must obtain a codepoint for the Timestamp Option from ISO. 4. Is it useful to pursue the use of the congestion experienced bit?