Network Working Group Simpson Internet Draft Daydreamer expires in six months January 1992 PPP LCP Extensions Status of this Memo This memo is the product of the Point-to-Point Protocol Working Group of the Internet Engineering Task Force (IETF). Comments on this memo should be submitted to the ietf-ppp@ucdavis.edu mailing list. Distribution of this memo is unlimited. 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 1id-abstracts.txt listing contained in the internet-drafts Shadow Directories on nic.ddn.mil, nnsc.nsf.net, nic.nordu.net, ftp.nisc.sri.com, or munnari.oz.au to learn the current status of any Internet Draft. Abstract The Point-to-Point Protocol (PPP) [1] provides a standard method of encapsulating Network Layer protocol information over point-to-point links. PPP also defines an extensible Link Control Protocol. This document defines several additional LCP features which have been suggested over the past year. Simpson expires in six months [Page i] DRAFT PPP LCP extensions January 1992 1. Additional LCP Packets The Packet format and basic facilities are already defined for LCP [1]. The most up-to-date values of the LCP Code field are specified in the most recent "Assigned Numbers" RFC [2]. This document concerns the following values: 13 Connect-Time Simpson expires in six months [Page 1] DRAFT PPP LCP extensions January 1992 1.1. Connect-Time 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 "dial-in server"). The session is concluded by the Terminate-Request packet. Implementation Note: This notification is defined as a separate LCP Code, rather 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 at the beginning of a session, and at regular intervals throughout the session, particularly near the end of the session. A summary of the Connect-Time 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 Connect-Time Identifier The Identifier field is one octet and is for use by the Connect- Time transmitter. Length >= 12 Simpson expires in six months [Page 2] DRAFT PPP LCP extensions January 1992 Seconds-Remaining The Seconds-Remaining field is four octets and indicates the number of integral seconds remaining in this session. This 32 bit 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 expires in six months [Page 3] DRAFT PPP LCP extensions January 1992 2. Additional LCP Configuration Options The Configuration Option format and basic options are already defined for LCP [1]. The most 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-Pad 13 Callback Simpson expires in six months [Page 4] DRAFT PPP LCP extensions January 1992 2.1. FCS-Alternatives Description This Configuration Option provides a way 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. More than one FCS Option MAY be present in the same Configure- Request, and any remaining FCS Options are Ack'd together. That is, if the implementations agree, each packet may have a different FCS. The negotiated FCS values take effect only during Authentication and Network-Layer Protocol phases. Packets sent during any other phase MUST contain the 16-bit FCS. The link can be subject to loss of state, and the LCP can re- negotiate at any time. When the LCP begins renegotiation, it is recommended that the LCP Configure-Request packet be sent with the last negotiated FCS, followed by another LCP Configure-Request packet with the 16-bit FCS. On receipt of a LCP Configure-Request or Terminate-Request packet, the implementation MUST change to the 16-bit FCS for both transmission and reception. The null FCS SHOULD only be used for those network-layer 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 an extraneous FCS is provided, any extra octets will appear to be padding. Therefore, the null FCS option MUST NOT be used with the Self-Describing-Pad Configuration Option (described below). When a configuration (LCP or NCP) or authentication packet is sent, a FCS MUST be included. When a configuration (LCP or NCP) or authentication packet is received, the FCS MUST be verified. Simpson expires in six months [Page 5] DRAFT PPP LCP extensions January 1992 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 | FCS | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 9 Length 3 FCS This field specifies the kind of FCS to be used on the link. 0 no FCS 16 16-bit FCS (default) 32 32-bit FCS Simpson expires in six months [Page 6] DRAFT PPP LCP extensions January 1992 2.2. Self-Describing-Pad Description This Configuration Option provides a way for an implementation to indicate to the peer that it understands self-describing pads when padding is added to the PPP Information field. This option is most likely to be used when network-layer protocols, particularly compression protocols, are configured which require detection and removal of any trailing pads. Such protocols are identified in thier respective NCP documents. If the option is Rejected, the peer MUST NOT add padding to such protocols, but MAY add padding to other protocols. If the option is Ack'd, the peer MUST add at least one octet of self-describing pad to such protocols, but is not required to add unnecessary 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 it does not understand the option, or when it never generates pads. While some implementations might only be capable of adding padding to every protocol or not adding padding to any protocol, by design the receiver need not examine protocols which do not need the pads 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 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; that is, three pad octets would contain the values 1, 2, 3. After removing the FCS, the final pad octet contains the number of pad octets to remove. Implementation Note: If any of the pad octets contain an incorrect index value, the entire frame SHOULD be silently discarded. This is intended to prevent confusion in an environment which understands more than one FCS, but might not be necessary in robust implementations. Simpson expires in six months [Page 7] DRAFT PPP LCP extensions January 1992 A summary of the Self-Describing-Pad Configuration 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 10 Length 2 Simpson expires in six months [Page 8] DRAFT PPP LCP extensions January 1992 2.3. Callback Description This Configuration Option provides a way for an implementation to request a dial-up peer to call back. This option might be used for many diverse purposes, such as perceived security or savings on toll charges. When callback is successfully negotiated, the Authentication phase proceeds directly to Termination phase. Implementation Note: 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 who to bill for the service. 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 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 telephone number 2 location identifier Simpson expires in six months [Page 9] DRAFT PPP LCP extensions January 1992 Message The Message field is zero or more octets, and its contents are determined by the Operation field. The size is determined from the Length field. Simpson expires in six months [Page 10] DRAFT PPP LCP extensions January 1992 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 expires in six months [Page 11] DRAFT PPP LCP extensions January 1992 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 PPP_INITFCS32 0xffffffff /* Initial FCS value */ #define PPP_GOODFCS32 0xfebb20e3 /* 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 expires in six months [Page 12] DRAFT PPP LCP extensions January 1992 fcs = (((fcs) >> 8) ^ fcstab_32[((fcs) ^ (*cp++)) & 0xff]); return (fcs); } main() { int len; u32 fcs; unsigned char buf[10]; fcs = PPP_INITFCS32; while ((len = read(0, buf, sizeof buf)) > 0) fcs = pppfcs32(fcs, buf, len); printf("0x%08X0, fcs); exit(0); } Simpson expires in six months [Page 13] DRAFT PPP LCP extensions January 1992 Security Considerations Security issues are not discussed in this memo. References [1] Simpson, W.A., "The Point-to-Point Protocol (PPP)", RFC 1331, May 1992. [2] Reynolds, J.K., Postel, J.B., "Assigned Numbers", RFC 1340, July 1992. Acknowledgments 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). The Self-Describing-Pad was suggested and named by Fred Baker (ACC). The Connect-Time feature was suggested by Brad Parker (then of Cayman). Chair's Address The working group can be contacted via the current chair: Brian Lloyd B.P. Lloyd & Associates, Inc. 3420 Sudbury Road Cameron Park, California 95682 Phone: (916) 676-1147 EMail: brian@lloyd.com Author's Address Questions about this memo can also be directed to: William Allen Simpson Daydreamer Computer Systems Consulting Services Simpson expires in six months [Page 14] DRAFT PPP LCP extensions January 1992 P O Box 6205 East Lansing, MI 48826-6205 EMail: Bill.Simpson@um.cc.umich.edu Simpson expires in six months [Page 15] DRAFT PPP LCP extensions January 1992 Table of Contents 1. Additional LCP Packets ................................ 1 1.1 Connect-Time .................................... 2 2. Additional LCP Configuration Options .................. 4 2.1 FCS-Alternatives ................................ 5 2.2 Self-Describing-Pad ............................. 7 2.3 Callback ........................................ 9 APPENDICES ................................................... 11 A. Fast Frame Check Sequence (FCS) Implementation ........ 11 A.1 32-bit FCS Computation Method ................... 11 SECURITY CONSIDERATIONS ...................................... 14 REFERENCES ................................................... 14 ACKNOWLEDGEMENTS ............................................. 14 CHAIR'S ADDRESS .............................................. 14 AUTHOR'S ADDRESS ............................................. 14