PPP Extensions Working Group Glenn McGregor Internet Draft Livingston Enterprises expires September 1997 March 1997 The PPP Internet Protocol Control Protocol (IPCP) draft-ietf-pppext-ipcp-network-01.txt 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 and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as ``work in progress.'' To learn the current status of any Internet-Draft, please check the ``1id-abstracts.txt'' listing contained in the Internet- Drafts Shadow Directories on ftp.is.co.za (Africa), ftp.nordu.net (Europe), munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or ftp.isi.edu (US West Coast). 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, and proposes a family of Network Control Protocols (NCPs) for establishing and configuring different network-layer protocols. This document defines the NCP for establishing and configuring the Internet Protocol [2] over PPP, and a method to negotiate and use Van Jacobson TCP/IP header compression [3] with PPP. McGregor expires September 1997 [Page i] INTERNET-DRAFT PPP IPCP March 1997 1. Introduction PPP has three main components: 1. A method for encapsulating datagrams over serial links. 2. A Link Control Protocol (LCP) for establishing, configuring, and testing the data-link connection. 3. A family of Network Control Protocols (NCPs) for establishing and configuring different network-layer protocols. In order to establish communications over a point-to-point link, each end of the PPP link must first send LCP packets to configure and test the data link. After the link has been established and optional facilities have been negotiated as needed by the LCP, PPP must send NCP packets to choose and configure one or more network-layer protocols. Once each of the chosen network-layer protocols has been configured, datagrams from each network-layer protocol can be sent over the link. The link will remain configured for communications until explicit LCP or NCP packets close the link down, or until some external event occurs (an inactivity timer expires or network administrator intervention). McGregor expires September 1997 [Page 1] INTERNET-DRAFT PPP IPCP March 1997 2. A PPP Network Control Protocol (NCP) for IP The IP Control Protocol (IPCP) is responsible for configuring, enabling, and disabling the IP protocol modules on both ends of the point-to-point link. IPCP uses the same packet exchange machanism as the Link Control Protocol (LCP). IPCP packets may not be exchanged until PPP has reached the Network-Layer Protocol phase. IPCP packets received before this phase is reached should be silently discarded. The IP Control Protocol is exactly the same as the Link Control Protocol [1] with the following exceptions: Data Link Layer Protocol Field Exactly one IPCP packet is encapsulated in the Information field of PPP Data Link Layer frames where the Protocol field indicates type hex 8021 (IP Control Protocol). Code field Only Codes 1 through 7 (Configure-Request, Configure-Ack, Configure-Nak, Configure-Reject, Terminate-Request, Terminate-Ack and Code-Reject) are used. Other Codes should be treated as unrecognized and should result in Code-Rejects. Timeouts IPCP packets may not be exchanged until PPP has reached the Network-Layer Protocol phase. An implementation should be prepared to wait for Authentication and Link Quality Determination to finish before timing out waiting for a Configure-Ack or other response. It is suggested that an implementation give up only after user intervention or a configurable amount of time. Configuration Option Types IPCP has a distinct set of Configuration Options, which are defined below. 2.1. Sending IP Datagrams Before any IP packets may be communicated, PPP must reach the Network-Layer Protocol phase, and the IP Control Protocol must reach the Opened state. Exactly one IP packet is encapsulated in the Information field of PPP Data Link Layer frames where the Protocol field indicates type hex 0021 (Internet Protocol). McGregor expires September 1997 [Page 2] INTERNET-DRAFT PPP IPCP March 1997 The maximum length of an IP packet transmitted over a PPP link is the same as the maximum length of the Information field of a PPP data link layer frame. Larger IP datagrams must be fragmented as necessary. If a system wishes to avoid fragmentation and reassembly, it should use the TCP Maximum Segment Size option [4], and MTU discovery [5]. McGregor expires September 1997 [Page 3] INTERNET-DRAFT PPP IPCP March 1997 3. IPCP Configuration Options IPCP Configuration Options allow negotiatiation of desirable Internet Protocol parameters. IPCP uses the same Configuration Option format defined for LCP [1], with a separate set of Options. The most up-to-date values of the IPCP Option Type field are specified in the most recent "Assigned Numbers" RFC [6]. Current values are assigned as follows: 1 IP-Addresses 2 IP-Compression-Protocol 3 IP-Address McGregor expires September 1997 [Page 4] INTERNET-DRAFT PPP IPCP March 1997 3.1. IP-Addresses Description The use of the Configuration Option IP-Addresses has been deprecated. It has been determined through implementation experience that it is difficult to ensure negotiation convergence in all cases using this option. RFC 1172 [7] provides information for implementations requiring backwards compatability. The IP- Address Configuration Option replaces this option, and its use is preferred. This option SHOULD NOT be sent in a Configure-Request if a Configure-Request has been received which includes either an IP- Addresses or IP-Address option. This option MAY be sent if a Configure-Reject is received for the IP-Address option, or a Configure-Nak is received with an IP-Addresses option as an appended option. Support for this option MAY be removed after the IPCP protocol status advances to Internet Draft Standard. McGregor expires September 1997 [Page 5] INTERNET-DRAFT PPP IPCP March 1997 3.2. IP-Compression-Protocol Description This Configuration Option provides a way to negotiate the use of a specific compression protocol. By default, compression is not enabled. A summary of the IP-Compression-Protocol Configuration 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 | IP-Compression-Protocol | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data ... +-+-+-+-+ Type 2 Length >= 4 IP-Compression-Protocol The IP-Compression-Protocol field is two octets and indicates the compression protocol desired. Values for this field are always the same as the PPP Data Link Layer Protocol field values for that same compression protocol. The most up-to-date values of the IP-Compression-Protocol field are specified in the most recent "Assigned Numbers" RFC [6]. Current values are assigned as follows: Value (in hex) Protocol 002d Van Jacobson Compressed TCP/IP Data The Data field is zero or more octets and contains additional data as determined by the particular compression protocol. McGregor expires September 1997 [Page 6] INTERNET-DRAFT PPP IPCP March 1997 Default No compression protocol enabled. McGregor expires September 1997 [Page 7] INTERNET-DRAFT PPP IPCP March 1997 3.3. IP-Address Description This Configuration Option provides a way to negotiate the IP address to be used on the local end of the link. It allows the sender of the Configure-Request to announce its IP-address, or to request that the peer provide the information. This request is indicated by an IP-address of all zeros (0.0.0.0). The peer can provide this information by sending a Configure-Nak with a valid IP-address. If the peer does not have an IP-address to assign, then it SHOULD return a Configure-Reject for this option. Due to possible confusion with the IPCP state machine going to open state, a Configure-Ack SHOULD NOT be used for this purpose. This option SHOULD be sent in a Configure-Request if the IP- address is known. If negotiation about the remote IP-address is required, and the peer did not provide the option in its Configure-Request, the option SHOULD be appended to a Configure-Nak. The value of the IP-address given must be acceptable as the remote IP-address, or indicate a request that the peer provide the information. By default, no IP address is assigned. A summary of the IP-Address Configuration 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 | IP-Address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IP-Address (cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 3 Length 6 McGregor expires September 1997 [Page 8] INTERNET-DRAFT PPP IPCP March 1997 IP-Address The four octet IP-Address is the desired local address of the sender of a Configure-Request. If all four octets are set to zero, it indicates a request that the peer provide the IP-Address information. Default No IP address is assigned. McGregor expires September 1997 [Page 9] INTERNET-DRAFT PPP IPCP March 1997 4. Van Jacobson TCP/IP header compression Van Jacobson TCP/IP header compression reduces the size of the TCP/IP headers to as few as three bytes. This can be a significant improvement on slow serial lines, particularly for interactive traffic. The IP-Compression-Protocol Configuration Option is used to indicate the ability to receive compressed packets. Each end of the link must seperately request this option if bi-directional compression is desired. The PPP Protocol field is set to the following values when transmitting IP packets: Value (in hex) 0021 Type IP. The IP protocol is not TCP, or the packet is a fragment, or cannot be compressed. 002d Compressed TCP. The TCP/IP headers are replaced by the compressed header. 002f Uncompressed TCP. The IP protocol field is replaced by the slot identifier. 4.1. Configuration Option Format A summary of the IP-Compression-Protocol Configuration Option format to negotiate Van Jacobson TCP/IP header compression 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 | IP-Compression-Protocol | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Max-Slot-Id | Comp-Slot-Id | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 2 Length 6 McGregor expires September 1997 [Page 10] INTERNET-DRAFT PPP IPCP March 1997 IP-Compression-Protocol 002d (hex) for Van Jacobson Compressed TCP/IP headers. Max-Slot-Id The Max-Slot-Id field is one octet and indicates the maximum slot identifier. This is one less than the actual number of slots; the slot identifier has values from zero to Max-Slot-Id. Note: There may be implementations that have problems with only one slot (Max-Slot-Id = 0). See the discussion in reference [3]. The example implementation in [3] will only work with 3 through 254 slots. Comp-Slot-Id The Comp-Slot-Id field is one octet and indicates whether the slot identifier field may be compressed. 0 The slot identifier must not be compressed. All compressed TCP packets must set the C bit in every change mask, and must include the slot identifier. 1 The slot identifer may be compressed. The slot identifier must not be compressed if there is no ability for the PPP link level to indicate an error in reception to the decompression module. Synchronization after errors depends on receiving a packet with the slot identifier. See the discussion in reference [3]. McGregor expires September 1997 [Page 11] INTERNET-DRAFT PPP IPCP March 1997 A. IPCP Recommended Options The following Configurations Options are recommended: IP-Compression-Protocol -- with at least 4 slots, usually 16 slots. IP-Address -- only on dial-up lines. Security Considerations Security issues are not discussed in this memo. References [1] Simpson, W. A., "The Point-to-Point Protocol", RFC in progress. [2] Postel, J., "Internet Protocol", RFC 791, USC/Information Sciences Institute, September 1981. [3] Jacobson, V., "Compressing TCP/IP Headers", RFC 1144, January 1990. [4] Postel, J., "The TCP Maximum Segment Size Option and Related Topics", RFC 879, USC/Information Sciences Institute, November 1983. [5] Mogul, J.C., Deering, S.E., "Path MTU Discovery", RFC 1191, November 1990. [6] Reynolds, J., Postel,J., "Assigned Numbers", RFC 1060, USC/Information Sciences Institute, March 1990. [7] Perkins, D., Hobby, R., "Point-to-Point Protocol (PPP) initial configuration options", RFC 1172, August 1990. Acknowledgments Some of the text in this document is taken from RFCs 1171 & 1172, by Drew Perkins of Carnegie Mellon University, and by Russ Hobby of the University of California at Davis. Information leading to the expanded IP-Compression option provided by Van Jacobson at SIGCOMM '90. McGregor expires September 1997 [Page 12] INTERNET-DRAFT PPP IPCP March 1997 Bill Simpson helped with the document formatting. Chair's Address The working group can be contacted via the current chair: Karl Fox Ascend Communications 3518 Riverside Drive, Suite 101 Columbus, Ohio 43221 Phone: (614) 326-6841 EMail: karl@ascend.com Author's Address Questions about this memo can also be directed to: Glenn McGregor Livingston Enterprises 3461 Robin Lane, Suite 1 Cameron Park, California 95682 Phone: (916) 676-6399 EMail: glenn@livingston.com McGregor expires September 1997 [Page 13] INTERNET-DRAFT PPP IPCP March 1997 TTTTaaaabbbblllleeee ooooffff CCCCoooonnnntttteeeennnnttttssss 1. Introduction .......................................... 1 2. A PPP Network Control Protocol (NCP) for IP ........... 2 2.1 Sending IP Datagrams ............................ 2 3. IPCP Configuration Options ............................ 4 3.1 IP-Addresses .................................... 5 3.2 IP-Compression-Protocol ......................... 6 3.3 IP-Address ...................................... 8 4. Van Jacobson TCP/IP header compression ................ 10 4.1 Configuration Option Format ..................... 10 APPENDICES ................................................... 12 A. IPCP Recommended Options .............................. 12 SECURITY CONSIDERATIONS ...................................... 12 REFERENCES ................................................... 12 ACKNOWLEDGEMENTS ............................................. 12 CHAIR'S ADDRESS .............................................. 13 AUTHOR'S ADDRESS ............................................. 13