IETF Page 1 January 6, 1993 CLNP for TUBA Internet Draft 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@eve.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 Page 2 Internet Draft CLNP for TUBA January 6, 1993 Many thanks to Ross Callon of Digital Equipment, Brian Carpenter of CERN, and Dave Katz of Cisco Systems for their assistance in composing this text. 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], in ASCII text. This is not the final version of the ISO protocol specification; however, 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 in CLNP header fields. Postscript versions of ISO CLNP and associated routing protocols are IETF Page 3 January 6, 1993 CLNP for TUBA Internet Draft available via anonymous FTP from merit.edu, and may be found in the directory /pub/iso.] 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. 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 Page 4 Internet Draft CLNP for TUBA January 6, 1993 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. Errors detected during the processing of a CLNP datagram may be reported using CLNP Error Reports. Implementations of CLNP for TUBA environments must be capable of processing Error Reports (this is consistent with the 1992 version of the ISO 8473 standard). Control messages (e.g., echo request/reply and redirect) are similarly handled in CLNP, i.e., identified as separate network layer packet types. The relationship between CLNP Error and Control messages and Internet Control Message Protocol (ICMP, [7]), and issues relating to the handling of these messages is described in Section 5. The composition and processing of a TCP pseudo-header when CLNP is used to provide the lower-level service expected by TCP and UDP is described in Section 6. 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 4-1: IETF Page 5 January 6, 1993 CLNP for TUBA Internet Draft 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 4-1. CLNP for TUBA Note 1: For illustrative purposes, Figure 4-1 depicts Destination and Source Addresses having a length of 19 octets, including the PROTO/reserved field. In general, addresses can be variable length, up to a maximu of 20 octets, including the PROTO/reserved field. IETF Page 6 Internet Draft CLNP for TUBA January 6, 1993 Note 2: Due to differences in link layer protocols, it is not possible to ensure that the packet starts on an even alignment. Note, however, that many link level protocols over which CLNP is operated happen to use a odd length link (e.g., 802.2). (As profiled in Figure 4-1, the rest of the CLNP packet is even-aligned.) The encoding of CLNP fields for use in TUBA environments is as follows. 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. The value 255 is reserved. The header length is the same for all fragments of the same (original) CLNP packet. [Note: General purpose CLNP implementations must be willing to accept addresses of variable length up to 20 octets. In particular, implementations that are expected to support both GOSIP and RFC 1237 [13] style addresses in addition to "TUBA" addresses [8]. must be capable of dealing with 20-octet addresses.] 4.3 Version This one-octet field identifies the version of the protocol; it must be 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.] IETF Page 7 January 6, 1993 CLNP for TUBA Internet Draft 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 "Don't Fragment" value of the Don't Fragment Flag of IP. [Editor's Note: If the Fragmentation Permitted field is set to the value O, then the Data Unit Identifier, Fragment Offset, and Total Length fields are not present. This denotes a single fragment datagram. In such datagrams, the Fragment Length field contains the total length of the datagram.] 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 from Echo packets. The following values of the type field apply: 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 +---+---+---+---+---+---+---+---+ | flags | 1 | 1 | 1 | 1 | 0 | => Encoding of Type = echo request +---+---+---+---+---+---+---+---+ | flags | 1 | 1 | 1 | 1 | 1 | => Encoding of Type = echo reply +---+---+---+---+---+---+---+---+ IETF Page 8 Internet Draft CLNP for TUBA January 6, 1993 Error Report packets are described in Section 5. Echo and its use is described in RFC 1139 [14]. 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 is computed on the header only. It is 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 for algorithms used in the computation and adjustment of the checksum. 4.9 Destination Address Length Indicator () This field indicates the length, in octets, of the Destination Address. 4.10 Destination Address The format of the address encoded in this field is described in a companion addressing document, see [8]. 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 may be between 8 and 20 octets long (inclusive). The final octet of the destination address 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. IETF Page 9 January 6, 1993 CLNP for TUBA Internet Draft 4.12 Source Address The format of the address encoded in this field is described in a companion addressing document, see [8]. 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 may be between 8 and 20 octets long (inclusive). The final octet of the source address is reserved. It may be set to the protocol field value on transmission, and shall be ignored on reception (the value of zero must not be used). 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. 4.15 Options All CLNP options are "triplets" 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. IETF Page 10 Internet Draft CLNP for TUBA January 6, 1993 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 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. IETF Page 11 January 6, 1993 CLNP for TUBA Internet Draft +-----------+----------+----------+----------+ | 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. [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 equivalent of the loose source route option of IP; i.e., a means for the source of an IETF Page 12 Internet Draft CLNP for TUBA January 6, 1993 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). The second octet identifies the offset of the next network entity title to be processed in the list, relative to the start of the parameter (i.e., a value of 3 is used to identify the first address in the list). The third octet begins the list of network entity titles. 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. The first octet of the parameter value is a type code, indicating Complete Source Route (0000 0001) Partial Recording of Route (0000 0000). The second octet identifies the offset where the next network entity title may be recorded (i.e., the end of the current list), relative to the start of the parameter (i.e., a value of 3 is used to identify the initial recording position). If recording of route has been terminated (I'll be back...), this octet has a value 255. The third octet begins the list of network entity titles. 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.] 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 IETF Page 13 January 6, 1993 CLNP for TUBA Internet Draft additional timestamp information. +--------+--------+--------+--------+ |11101110| length | pointer|oflw|flg| +--------+--------+--------+--------+ | network entity title | +--------+--------+--------+--------+ | timestamp | +--------+--------+--------+--------+ | . | . 5. Error Reporting and Control Message Handling 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. ICMP messages are transmitted as user data in IP datagrams. Unreachable destinations, incorrectly composed IP datagram headers, IP datagram discards due to congestion, and lifetime/reassembly time exceeded are reported; the complete internet header that caused the error plus 8 octets of the segment contained in that IP datagram are returned to the sender as part of the ICMP error message. For certain errors, e.g., incorrectly composed IP datagram headers, the specific octet which caused the problem is identified. In CLNP environments, an unique message type, the Error Report type, is used in the network layer protocol header to distinguish Error Reports from CLNP datagrams. CLNP Error Reports are generated on detection of the same types of errors as with ICMP. Like ICMP error messages, the complete CLNP header that caused the error is returned to the sender in the data portion of the Error Report. Implementations should return at least 8 octets of the datagram contained in the CLNP datagram to the sender of the original CLNP datagram. Here too, for certain errors, the specific octet which caused the problem is identified A summary of the contents of the CLNP Error Report, as it is proposed for use in TUBA environments, is illustrated in Figure 5-1: IETF Page 14 Internet Draft CLNP for TUBA January 6, 1993 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)| 000 | Type=ER | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TOTAL Length of Error Report | 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 | Reason for Discard (type/len) | | | 1100 0001 | 0000 0010 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Reason for Discard | Options... | | code | pointer | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options | : : | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Note that each tick mark represents one bit position. Figure 5-1. Error Report Format 5.1 Rules for processing an Error Report The following is a summary of the rules for processing an Error Report: IETF Page 15 January 6, 1993 CLNP for TUBA Internet Draft o+ An Error Report is not generated to report a problem encountered while processing an Error Report. o+ Error Reports may not be fragmented (hence, the fragmentation part is absent). o+ The Reason for Discard Code field is populated with one of the values from Table 5-1. o+ The Pointer field is populated with number of the first octet of the field that caused the Error Report to be generated. If it is not possible to identify the offending octet, this field must be zeroed. o+ If the Priority or Type of Service option is present in the errored datagram, the Error Report shall specify the same option, using the value specified in the original datagram. o+ If the Security option is present in the errored datagram, the Error Report shall specify the same option, using the value specified in the original datagram; if the Security option is not supported, no Error Report is to be generated. o+ If the Complete Source Route option is specified in the errored datagram, the Error Report must compose a reverse of that route, and return the datagram along the same path. 5.2 Comparison of ICMP and CLNP Error Messages Table 5-1 provides a loose comparison of ICMP message types and codes to CLNP Error Type Codes (values in Internet ASCII): IETF Page 16 Internet Draft CLNP for TUBA January 6, 1993 CLNP Error Type Codes | ICMP Message (Type, Code) ----------------------------------|------------------------------------ Reason not specified (0) | Parameter Problem (12, 0) Protocol Procedure Error (1) | Parameter Problem (12, 0) Incorrect Checksum (2) | Parameter Problem (12, 0) PDU Discarded--Congestion (3) | Source Quench (4, 0) Header Syntax Error (4) | Parameter problem (12, 0) Need to Fragment could not (5) | Frag needed, DF set (3, 4) Incomplete PDU received (6) | Parameter Problem (12, 0) Duplicate Option (7) | Parameter Problem (12, 0) Destination Unreachable (128) | Network Unreachable (3, 0) Destination Unknown (129) | Host Unreachable (3, 1) Source Routing Error (144) | Source Route failed (3, 5) Source Route Syntax Error (145) | Source Route failed (3, 5) Unknown Address in Src Route(146) | Source Route failed (3, 5) Path not acceptable (147) | Source Route failed (3, 5) Lifetime expired (160) | TTL exceeded (11, 0) Reassembly Lifetime Expired (161) | Reassembly time exceeded (11, 1) Unsupported Option (176) | Parameter Problem (12, 0) Unsupported Protocol Version(177) | Parameter problem (12, 0) Unsupported Security Option (178) | Parameter problem (12, 0) Unsupported Src Rte Option (179) | Parameter problem (12, 0) Unsupported Rcrd Rte (180) | Parameter problem (12, 0) Reassembly interference (192) | Reassembly time exceeded (11,1) Table 5-1. Comparison of CLNP Error Reports to ICMP Error Messages 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: There are no corresponding CLNP Error Report Codes for the following ICMP error message types: - Protocol Unreachable (3, 2) - Port Unreachable (3, 3) [ED. There are error code points available in the ER type code block that can be used to identify these message types.] 6. Pseudo-Header Considerations A checksum is computed on UDP and TCP segments to verify the integrity of the UDP/TCP segment. To further verify that the UDP/TCP segment has arrived at its correct destination, a pseudo-header consisting of information used in the delivery of the UDP/TCP segment is composed and included in the checksum computation. IETF Page 17 January 6, 1993 CLNP for TUBA Internet Draft To compute the checksum on a UDP or TCP segment prior to transmission, implementations must compose a pseudo-header to the UDP/TCP segment consisting of the following information that will be used when composing the CLNP datagram: o+ Destination Address Length Indicator o+ Destination Address and PROTO o+ Source Address Length Indicator o+ Source Address and Reserved The total length of the UDP/TCP segment is also included in the checksum computation. Figure 5-1 illustrates the resulting pseudo-header when both source and destination addresses are maximum length. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 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 | UDP/TCP segment length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5-1. Pseudo-header If needed, an octet of zero is added to the end of the UDP/TCP segment to pad the datagram to a length that is a multiple of 16 bits. In all other respects, rules for computing the checksum are consistent with RFC 793 and RFC 768. IETF Page 18 Internet Draft CLNP for TUBA January 6, 1993 7. REFERENCES IETF Page 19 January 6, 1993 CLNP for TUBA Internet Draft [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 Control Protocol (TCP). Request for Comments 793, Network Information Center, SRI International, Menlo Park, CA, 1981 September. [4] Postel, J., User Datagram Protocol (UDP). Request for Comments 768, Network Information Center, SRI International, Menlo Park, CA. [5] Postel, J., Internet Protocol (IP). Request for Comments 791, Network Information Center, SRI International, Menlo Park, CA, 1981 September. [6] Chapin, L., ISO CLNP, Draft International Standard version, Request for Comments 994, Network Information Center, SRI International, Menlo Park, CA. [7] ISO 8348--International Standards Organization--Data Communications--OSI Network Layer Addressing [8] Callon, R., Addressing for the new Internet. Request for Comments iiii, Network Information Center, SRI International, Menlo Park, CA. [9] Reynolds, J., and J. Postel, Assigned Numbers. Request for Comments 1340, Network Information Center, SRI International, Menlo Park, CA. [10] Kent, S., Security Option for IP, Request for Comments 1108, Network Information Center, SRI International, Menlo Park, CA. [11] Almquist, P., Type of Service in the Internet Protocol Suite. Request for Comments 1349, Network Information Center, SRI International, Menlo Park, CA. [12] ISO 6523 -- International Code Designators [13] Callon, R., NSAPA Guidelines for the Internet, Request for Comments RFC 1237, Network Information Center, SRI International, Menlo Park, CA. [14] Hagens, R. and C. Wittbrodt, CLNP Ping, Request for Comments 1139, Network Information Center, SRI International, Menlo Park, CA. IETF Page 20 Internet Draft CLNP for TUBA January 6, 1993 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 Page 21 January 6, 1993 CLNP for TUBA Internet Draft 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