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diff --git a/doc/rfc1570.txt b/doc/rfc1570.txt new file mode 100644 index 00000000..edda5d99 --- /dev/null +++ b/doc/rfc1570.txt @@ -0,0 +1,1057 @@ + + + + + + +Network Working Group W. Simpson, Editor +Request for Comments: 1570 Daydreamer +Updates: 1548 January 1994 +Category: Standards Track + + + PPP LCP Extensions + +Status of this Memo + + This document specifies an Internet standards track protocol for the + Internet community, and requests discussion and suggestions for + improvements. Please refer to the current edition of the "Internet + Official Protocol Standards" (STD 1) for the standardization state + and status of this protocol. Distribution of this memo is unlimited. + +Abstract + + The Point-to-Point Protocol (PPP) [1] provides a standard method for + transporting multi-protocol datagrams over point-to-point links. PPP + defines an extensible Link Control Protocol (LCP) for establishing, + configuring, and testing the data-link connection. This document + defines several additional LCP features which have been suggested + over the past few years. + + This document is the product of the Point-to-Point Protocol Working + Group of the Internet Engineering Task Force (IETF). Comments should + be submitted to the ietf-ppp@ucdavis.edu mailing list. + +Table of Contents + + 1. Additional LCP Packets ................................ 1 + 1.1 Identification .................................. 1 + 1.2 Time-Remaining .................................. 3 + 2. Additional LCP Configuration Options .................. 6 + 2.1 FCS-Alternatives ................................ 6 + 2.1.1 LCP considerations .............................. 7 + 2.1.2 Null FCS ........................................ 8 + 2.2 Self-Describing-Padding ......................... 9 + 2.3 Callback ........................................ 11 + 2.4 Compound-Frames ................................. 12 + 2.4.1 LCP considerations .............................. 14 + APPENDICES ................................................... 15 + A. Fast Frame Check Sequence (FCS) Implementation ........ 15 + A.1 32-bit FCS Computation Method ................... 15 + SECURITY CONSIDERATIONS ...................................... 17 + REFERENCES ................................................... 17 + ACKNOWLEDGEMENTS ............................................. 18 + CHAIR'S ADDRESS .............................................. 18 + EDITOR'S ADDRESS ............................................. 18 + + + + + + + + +Simpson [Page i] + RFC 1570 PPP LCP extensions January 1994 + + +1. Additional LCP Packets + + The Packet format and basic facilities are already defined for LCP + [1]. + + Up-to-date values of the LCP Code field are specified in the most + recent "Assigned Numbers" RFC [2]. This specification concerns the + following values: + + 12 Identification + 13 Time-Remaining + + + + +1.1. Identification + + Description + + This Code provides a method for an implementation to identify + itself to its peer. This Code might be used for many diverse + purposes, such as link troubleshooting, license enforcement, etc. + + Identification is a Link Maintenance packet. Identification + packets MAY be sent at any time, including before LCP has reached + the Opened state. + + The sender transmits a LCP packet with the Code field set to 12 + (Identification), the Identifier field set, the local Magic-Number + (if any) inserted, and the Message field filled with any desired + data, but not exceeding the default MRU minus eight. + + Receipt of an Identification packet causes the RXR or RUC event. + There is no response to the Identification packet. + + Receipt of a Code-Reject for the Identification packet SHOULD + generate the RXJ+ (permitted) event. + + Rationale: + + This feature is defined as part of LCP, rather than as a + separate PPP Protocol, in order that its benefits may be + available during the earliest possible stage of the Link + Establishment phase. It allows an operator to learn the + identification of the peer even when negotiation is not + converging. Non-LCP packets cannot be sent during the Link + Establishment phase. + + + + +Simpson [Page 1] + RFC 1570 PPP LCP extensions January 1994 + + + This feature is defined as a separate LCP Code, rather than a + Configuration-Option, so that the peer need not include it with + other items in configuration packet exchanges, and handle + "corrected" values or "rejection", since its generation is both + rare and in one direction. It is recommended that + Identification packets be sent whenever a Configure-Reject is + sent or received, as a final message when negotiation fails to + converge, and when LCP reaches the Opened state. + + A summary of the Identification packet format is shown below. The + fields are transmitted from left to right. + + 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 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Code | Identifier | Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Magic-Number | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Message ... + +-+-+-+-+-+-+-+-+ + + + Code + + 12 for Identification + + Identifier + + The Identifier field MUST be changed for each Identification sent. + + Length + + >= 8 + + Magic-Number + + The Magic-Number field is four octets and aids in detecting links + which are in the looped-back condition. Until the Magic-Number + Configuration Option has been successfully negotiated, the Magic- + Number MUST be transmitted as zero. See the Magic-Number + Configuration Option for further explanation. + + Message + + The Message field is zero or more octets, and its contents are + implementation dependent. It is intended to be human readable, + and MUST NOT affect operation of the protocol. It is recommended + + + +Simpson [Page 2] + RFC 1570 PPP LCP extensions January 1994 + + + that the message contain displayable ASCII characters 32 through + 126 decimal. Mechanisms for extension to other character sets are + the topic of future research. The size is determined from the + Length field. + + Implementation Note: + + The Message will usually contain such things as the sender's + hardware type, PPP software revision level, and PPP product + serial number, MIB information such as link speed and interface + name, and any other information that the sender thinks might be + useful in debugging connections. The format is likely to be + different for each implementor, so that those doing serial + number tracking can validate their numbers. A robust + implementation SHOULD treat the Message as displayable text, + and SHOULD be able to receive and display a very long Message. + + + +1.2. Time-Remaining + + Description + + This Code provides a mechanism for notifying the peer of the time + remaining in this session. + + The nature of this information is advisory only. It is intended + that only one side of the connection will send this packet + (generally a "network access server"). The session is actually + concluded by the Terminate-Request packet. + + Time-Remaining is a Link Maintenance packet. Time-Remaining + packets may only be sent in the LCP Opened state. + + The sender transmits a LCP packet with the Code field set to 13 + (Time-Remaining), the Identifier field set, the local Magic-Number + (if any) inserted, and the Message field filled with any desired + data, but not exceeding the peer's established MRU minus twelve. + + Receipt of an Time-Remaining packet causes the RXR or RUC event. + There is no response to the Time-Remaining packet. + + Receipt of a Code-Reject for the Time-Remaining packet SHOULD + generate the RXJ+ (permitted) event. + + Rationale: + + This notification is defined as a separate LCP Code, rather + + + +Simpson [Page 3] + RFC 1570 PPP LCP extensions January 1994 + + + than a Configuration-Option, in order that changes and warning + messages may occur dynamically during the session, and that the + information might be determined after Authentication has + occurred. Typically, this packet is sent when the link enters + Network-Layer Protocol phase, and at regular intervals + throughout the session, particularly near the end of the + session. + + A summary of the Time-Remaining packet format is shown below. The + fields are transmitted from left to right. + + 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 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Code | Identifier | Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Magic-Number | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Seconds-Remaining | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Message ... + +-+-+-+-+-+-+-+-+ + + + Code + + 13 for Time-Remaining + + Identifier + + The Identifier field MUST be changed for each Time-Remaining sent. + + Length + + >= 12 + + Magic-Number + + The Magic-Number field is four octets and aids in detecting links + which are in the looped-back condition. Until the Magic-Number + Configuration Option has been successfully negotiated, the Magic- + Number MUST be transmitted as zero. See the Magic-Number + Configuration Option for further explanation. + + Seconds-Remaining + + The Seconds-Remaining field is four octets and indicates the + number of integral seconds remaining in this session. This 32 bit + + + +Simpson [Page 4] + RFC 1570 PPP LCP extensions January 1994 + + + unsigned value is sent most significant octet first. A value of + 0xffffffff (all ones) represents no timeout, or "forever". + + Message + + The Message field is zero or more octets, and its contents are + implementation dependent. It is intended to be human readable, + and MUST NOT affect operation of the protocol. It is recommended + that the message contain displayable ASCII characters 32 through + 126 decimal. Mechanisms for extension to other character sets are + the topic of future research. The size is determined from the + Length field. + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +Simpson [Page 5] + RFC 1570 PPP LCP extensions January 1994 + + +2. Additional LCP Configuration Options + + The Configuration Option format and basic options are already defined + for LCP [1]. + + Up-to-date values of the LCP Option Type field are specified in the + most recent "Assigned Numbers" RFC [2]. This document concerns the + following values: + + 9 FCS-Alternatives + 10 Self-Describing-Padding + 13 Callback + 15 Compound-Frames + + + + +2.1. FCS-Alternatives + + Description + + This Configuration Option provides a method for an implementation + to specify another FCS format to be sent by the peer, or to + negotiate away the FCS altogether. + + This option is negotiated separately in each direction. However, + it is not required that an implementation be capable of + concurrently generating a different FCS on each side of the link. + + The negotiated FCS values take effect only during Authentication + and Network-Layer Protocol phases. Frames sent during any other + phase MUST contain the default FCS. + + A summary of the FCS-Alternatives Configuration Option format is + shown below. The fields are transmitted from left to right. + + 0 1 2 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Type | Length | Options | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + + Type + + 9 + + + + + +Simpson [Page 6] + RFC 1570 PPP LCP extensions January 1994 + + + Length + + 3 + + Options + + This field is one octet, and is comprised of the "logical or" of + the following values: + + 1 Null FCS + 2 CCITT 16-bit FCS + 4 CCITT 32-bit FCS + + + Implementation Note: + + For most PPP HDLC framed links, the default FCS is the CCITT 16- + bit FCS. Some framing techniques and high speed links may use + another format as the default FCS. + + +2.1.1. LCP considerations + + The link can be subject to loss of state, and the LCP can re- + negotiate at any time. When the LCP begins renegotiation or + termination, it is recommended that the LCP Configure-Request or + Terminate-Request packet be sent with the last negotiated FCS, then + change to the default FCS, and a duplicate LCP packet is sent with + the default FCS. The Identifier field SHOULD NOT be incremented for + each such duplicate packet. + + On receipt of a LCP Configure-Request or Terminate-Request packet, + the implementation MUST change to the default FCS for both + transmission and reception. If a Request packet is received which + contains a duplicate Identifier field, a new reply MUST be generated. + + Implementation Notes: + + The need to send two packets is only necessary after the + Alternative-FCS has already been negotiated. It need not occur + during state transitions when there is a natural indication that + the default FCS is in effect, such as the Down and Up events. It + is necessary to send two packets in the Ack-Sent and Opened + states, since the peer could mistakenly believe that the link has + Opened. + + It is possible to send a single 48-bit FCS which is a combination + of the 16-bit and 32-bit FCS. This may be sent instead of sending + + + +Simpson [Page 7] + RFC 1570 PPP LCP extensions January 1994 + + + the two packets described above. We have not standardized this + procedure because of intellectual property concerns. If such a + 48-bit FCS is used, it MUST only be used for LCP packets. + + +2.1.2. Null FCS + + The Null FCS SHOULD only be used for those network-layer and + transport protocols which have an end-to-end checksum available, such + as TCP/IP, or UDP/IP with the checksum enabled. That is, the Null + FCS option SHOULD be negotiated together with another non-null FCS + option in a heterogeneous environment. + + When a configuration (LCP or NCP) or authentication packet is sent, + the FCS MUST be included. When a configuration (LCP or NCP) or + authentication packet is received, the FCS MUST be verified. + + There are several cases to be considered: + + Null FCS alone + + The sender generates the FCS for those frames which require the + FCS before sending the frame. + + When a frame is received, it is not necessary to check the FCS + before demultiplexing. Any FCS is treated as padding. + + Receipt of an Authentication or Control packet would be discovered + after passing the frame to the demultiplexer. Verification of the + FCS can easily be accomplished using one of the software + algorithms defined in "PPP in HDLC Framing" [3] (16-bit FCS) and + Appendix A (32-bit FCS). + + Null FCS with another FCS, using software + + This is similar to the above case. + + Those packets which are required to have the FCS (Authentication, + Control, or Network-Protocols lacking a checksum) are checked + using software after demultiplexing. Packets which fail the FCS + test are discarded as usual. + + Null FCS with another FCS, using hardware + + A flag is passed with the frame, indicating whether or not it has + passed the hardware FCS check. The incorrect FCS MUST be passed + with the rest of the data. The frame MUST NOT be discarded until + after demultiplexing, and only those frames that require the FCS + + + +Simpson [Page 8] + RFC 1570 PPP LCP extensions January 1994 + + + are discarded. + + All three FCS forms (Null, 16 and 32) may be used concurrently on + different frames when using software. That is probably not possible + with most current hardware. + + + +2.2. Self-Describing-Padding + + Description + + This Configuration Option provides a method for an implementation + to indicate to the peer that it understands self-describing pads + when padding is added at the end of the PPP Information field. + + This option is most likely to be used when some protocols, such as + network-layer or compression protocols, are configured which + require detection and removal of any trailing padding. Such + special protocols are identified in their respective documents. + + If the option is Rejected, the peer MUST NOT add any padding to + the identified special protocols, but MAY add padding to other + protocols. + + If the option is Ack'd, the peer MUST follow the procedures for + adding self-describing pads, but only to the specifically + identified protocols. The peer is not required to add any padding + to other protocols. + + Implementation Notes: + + This is defined so that the Reject handles either case where + the peer does not generate self-describing pads. When the peer + never generates padding, it may safely Reject the option. When + the peer does not understand the option, it also will not + successfully configure a special protocol which requires + elimination of pads. + + While some senders might only be capable of adding padding to + every protocol or not adding padding to any protocol, by design + the receiver need not examine those protocols which do not need + the padding stripped. + + To avoid unnecessary configuration handshakes, an + implementation which generates padding, and has a protocol + configured which requires the padding to be known, SHOULD + include this Option in its Configure-Request, and SHOULD + + + +Simpson [Page 9] + RFC 1570 PPP LCP extensions January 1994 + + + Configure-Nak with this Option when it is not present in the + peer's Request. + + Each octet of self-describing pad contains the index of that + octet. The first pad octet MUST contain the value one (1), which + indicates the Padding Protocol to the Compound-Frames option. + After removing the FCS, the final pad octet indicates the number + of pad octets to remove. For example, three pad octets would + contain the values 1, 2, 3. + + The Maximum-Pad-Value (MPV) is also negotiated. Only the values 1 + through MPV are used. When no padding would otherwise be + required, but the final octet of the PPP Information field + contains the value 1 through MPV, at least one self-describing pad + octet MUST be added to the frame. If the final octet is greater + than MPV, no additional padding is required. + + Implementation Notes: + + If any of the pad octets contain an incorrect index value, the + entire frame SHOULD be silently discarded. This is intended to + prevent confusion with the FCS-Alternatives option, but might + not be necessary in robust implementations. + + Since this option is intended to support compression protocols, + the Maximum-Pad-Value is specified to limit the likelihood that + a frame may actually become longer. + + A summary of the Self-Describing-Padding Configuration Option format + is shown below. The fields are transmitted from left to right. + + 0 1 2 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Type | Length | Maximum | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + + Type + + 10 + + Length + + 3 + + + + + + +Simpson [Page 10] + RFC 1570 PPP LCP extensions January 1994 + + + Maximum + + This field specifies the largest number of padding octets which + may be added to the frame. The value may range from 1 to 255, but + values of 2, 4, or 8 are most likely. + + + +2.3. Callback + + Description + + This Configuration Option provides a method for an implementation + to request a dial-up peer to call back. This option might be used + for many diverse purposes, such as savings on toll charges. + + When Callback is successfully negotiated, and authentication is + complete, the Authentication phase proceeds directly to the + Termination phase, and the link is disconnected. + + Then, the peer re-establishes the link, without negotiating + Callback. + + Implementation Notes: + + A peer which agrees to this option SHOULD request the + Authentication-Protocol Configuration Option. The user + information learned during authentication can be used to + determine the user location, or to limit a user to certain + locations, or merely to determine whom to bill for the service. + + Authentication SHOULD be requested in turn by the + implementation when it is called back, if mutual authentication + is desired. + + A summary of the Callback Option format is shown below. The fields + are transmitted from left to right. + + 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 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Type | Length | Operation | Message ... + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + + Type + + 13 + + + +Simpson [Page 11] + RFC 1570 PPP LCP extensions January 1994 + + + Length + + >= 3 + + Operation + + The Operation field is one octet and indicates the contents of the + Message field. + + 0 location is determined by user authentication + + 1 Dialing string, the format and contents of which assumes + configuration knowledge of the specific device which is + making the callback. + + 2 Location identifier, which may or may not be human + readable, to be used together with the authentication + information for a database lookup to determine the + callback location. + + 3 E.164 number. + + 4 Distinguished name. + + Message + + The Message field is zero or more octets, and its general contents + are determined by the Operation field. The actual format of the + information is site or application specific, and a robust + implementation SHOULD support the field as undistinguished octets. + The size is determined from the Length field. + + It is intended that only an authorized user will have correct site + specific information to make use of the Callback. The + codification of the range of allowed usage of this field is + outside the scope of this specification. + + + +2.4. Compound-Frames + + Description + + This Configuration Option provides a method for an implementation + to send multiple PPP encapsulated packets within the same frame. + This option might be used for many diverse purposes, such as + savings on toll charges. + + + + +Simpson [Page 12] + RFC 1570 PPP LCP extensions January 1994 + + + Only those PPP Protocols which have determinate lengths or + integral length fields may be aggregated into a compound frame. + + When Compound-Frames is successfully negotiated, the sender MAY + add additional packets to the same frame. Each packet is + immediately followed by another Protocol field, with its attendant + datagram. + + When padding is added to the end of the Information field, the + procedure described in Self-Describing-Padding is used. + Therefore, this option MUST be negotiated together with the Self- + Describing-Padding option. + + If the FCS-Alternatives option has been negotiated, self + describing padding MUST always be added. That is, the final + packet MUST be followed by a series of octets, the first of which + contains the value one (1). + + On receipt, the first Protocol field is examined, and the packet + is processed as usual. For those datagrams which have a + determinate length, the remainder of the frame is returned to the + demultiplexor. Each succeeding Protocol field is processed as a + separate packet. This processing is complete when a packet is + processed which does not have a determinate length, when the + remainder of the frame is empty, or when the Protocol field is + determined to have a value of one (1). + + The PPP Protocol value of one (1) is reserved as the Padding + Protocol. Any following octets are removed as padding. + + A summary of the Compound-Frames Option format is shown below. The + fields are transmitted from left to right. + + 0 1 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | Type | Length | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + + + Type + + 15 + + Length + + 2 + + + + +Simpson [Page 13] + RFC 1570 PPP LCP extensions January 1994 + + +2.4.1. LCP considerations + + During initial negotiation, the Compound-Frames option can be used to + minimize the negotiation latency, by reducing the number of frames + exchanged. + + The first LCP Configure-Request packet is sent as usual in a single + frame, including the Self-Describing-Padding and Compound-Frames + options. + + The peer SHOULD respond with a Configure-Ack, followed in a compound + frame by its LCP Configure-Request, and any NCP Configure-Requests + desired. + + Upon receipt, the local implementation SHOULD process the Configure- + Ack as usual. Since the peer has agreed to send compound frames, the + implementation MUST examine the remainder of the frame for additional + packets. If the peer also specified the Self-Describing-Padding and + Compound-Frames options in its Configure-Request, the local + implementation SHOULD retain its Configure-Ack, and further NCP + configuration packets SHOULD be added to the return frame. + + Together with the peer's final return frame, the minimum number of + frames to complete configuration is 4. + + + + + + + + + + + + + + + + + + + + + + + + + + + +Simpson [Page 14] + RFC 1570 PPP LCP extensions January 1994 + + +A. Fast Frame Check Sequence (FCS) Implementation + +A.1. 32-bit FCS Computation Method + + The following code provides a table lookup computation for + calculating the 32-bit Frame Check Sequence as data arrives at the + interface. + + /* + * u32 represents an unsigned 32-bit number. Adjust the typedef for + * your hardware. + */ + typedef unsigned long u32; + + static u32 fcstab_32[256] = + { + 0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, + 0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3, + 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988, + 0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, + 0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de, + 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7, + 0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, + 0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5, + 0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172, + 0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, + 0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940, + 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59, + 0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, + 0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f, + 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924, + 0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, + 0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a, + 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433, + 0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, + 0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01, + 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e, + 0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, + 0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c, + 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65, + 0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, + 0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb, + 0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0, + 0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9, + 0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086, + 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f, + 0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, + 0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad, + + + +Simpson [Page 15] + RFC 1570 PPP LCP extensions January 1994 + + + 0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a, + 0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683, + 0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8, + 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1, + 0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, + 0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7, + 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc, + 0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, + 0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252, + 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b, + 0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, + 0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79, + 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236, + 0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, + 0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04, + 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d, + 0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, + 0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713, + 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38, + 0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, + 0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e, + 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777, + 0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, + 0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45, + 0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2, + 0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db, + 0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0, + 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9, + 0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, + 0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf, + 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94, + 0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d + }; + + #define PPPINITFCS32 0xffffffff /* Initial FCS value */ + #define PPPGOODFCS32 0xdebb20e3 /* Good final FCS value */ + + /* + * Calculate a new FCS given the current FCS and the new data. + */ + u32 pppfcs32(fcs, cp, len) + register u32 fcs; + register unsigned char *cp; + register int len; + { + ASSERT(sizeof (u32) == 4); + ASSERT(((u32) -1) > 0); + while (len--) + + + +Simpson [Page 16] + RFC 1570 PPP LCP extensions January 1994 + + + fcs = (((fcs) >> 8) ^ fcstab_32[((fcs) ^ (*cp++)) & 0xff]); + + return (fcs); + } + + /* + * How to use the fcs + */ + tryfcs32(cp, len) + register unsigned char *cp; + register int len; + { + u32 trialfcs; + + /* add on output */ + trialfcs = pppfcs32( PPPINITFCS32, cp, len ); + trialfcs ^= 0xffffffff; /* complement */ + cp[len] = (trialfcs & 0x00ff); /* Least significant byte first */ + cp[len+1] = ((trialfcs >>= 8) & 0x00ff); + cp[len+2] = ((trialfcs >>= 8) & 0x00ff); + cp[len+3] = ((trialfcs >> 8) & 0x00ff); + + /* check on input */ + trialfcs = pppfcs32( PPPINITFCS32, cp, len + 4 ); + if ( trialfcs == PPPGOODFCS32 ) + printf("Good FCS\n"); + } + + +Security Considerations + + Security issues are briefly discussed in sections concerning the + Callback Configuration Option. + + +References + + [1] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)", RFC + 1548, Daydreamer, December 1993. + + [2] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, + RFC 1340, USC/Information Sciences Institute, July 1992. + + [3] Simpson, W., Editor, "PPP in HDLC Framing", RFC 1549, + Daydreamer, December 1993. + + + + + + +Simpson [Page 17] + RFC 1570 PPP LCP extensions January 1994 + + +Acknowledgments + + The Identification feature was suggested by Bob Sutterfield (Morning + Star Technologies). + + The Time-Remaining feature was suggested by Brad Parker (FCR). + + Some of the original text for FCS-Alternatives was provided by Arthur + Harvey (then of DEC). The Null FCS was requested by Peter Honeyman + (UMich). The 32-bit FCS example code was provided by Karl Fox + (Morning Star Technologies). + + Self-Describing-Padding was suggested and named by Fred Baker (ACC). + + Compound-Frames was suggested by Keith Sklower (Berkeley). + + Special thanks to Morning Star Technologies for providing computing + resources and network access support for writing this specification. + + +Chair's Address + + The working group can be contacted via the current chair: + + Fred Baker + Advanced Computer Communications + 315 Bollay Drive + Santa Barbara, California 93117 + + EMail: fbaker@acc.com + + +Editor's Address + + Questions about this memo can also be directed to: + + William Allen Simpson + Daydreamer + Computer Systems Consulting Services + 1384 Fontaine + Madison Heights, Michigan 48071 + + EMail: Bill.Simpson@um.cc.umich.edu + bsimpson@MorningStar.com + + + + + + + +Simpson [Page 18] + + |