Network Working Group G McGregor Internet Draft Merit August 1991 The PPP Internet Protocol Control Protocol (IPCP) Status of this Memo This document will be submitted to the RFC Editor as a protocol specification. Please refer to the current edition of the "IAB Official Protocol Standards" for the standardization state and status of this protocol. This proposal 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 Point-to-Point Protocol Working Group chair. Distribution of this memo is unlimited. 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 [Page i] Internet Draft PPP IPCP August 1991 Table of Contents 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 ......................... 7 4. Van Jacobson TCP/IP header compression ................ 9 4.1 Configuration Option Format ..................... 9 APPENDICES ................................................... 11 A. IPCP event cookbook ................................... 11 B. IPCP Recommended Options .............................. 11 REFERENCES ................................................... 12 SECURITY CONSIDERATIONS ...................................... 12 ACKNOWLEDGEMENTS ............................................. 12 CHAIR'S ADDRESS .............................................. 12 AUTHOR'S ADDRESS ............................................. 13 McGregor [Page ii] Internet Draft PPP IPCP August 1991 1. Introduction PPP has three main components: 1. A method for encapsulating datagrams over serial links. PPP uses HDLC as a basis for encapsulating datagrams over point- to-point links. At this time, PPP specifies the use of asynchronous or synchronous duplex circuits, either dedicated or circuit switched. 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. PPP is designed to allow the simultaneous use of multiple 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 [Page 1] Internet Draft PPP IPCP August 1991 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. Likewise, IP datagrams may not be exchanged until IPCP has finished opening the connection (reached the Opened state). 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 McGregor [Page 2] Internet Draft PPP IPCP August 1991 Data Link Layer frames where the Protocol field indicates type hex 0021 (Internet Protocol). 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 [Page 3] Internet Draft PPP IPCP August 1991 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 McGregor [Page 4] Internet Draft PPP IPCP August 1991 3.1. IP-Addresses Description This Configuration Option provides a way to negotiate the IP addresses to be used on each end of the link. By default, no IP addresses are assigned to either end. An address specified as zero shall be interpreted as requesting the peer to specify the address. If an implementation allows the assignment of multiple IP addresses, then it may include multiple IP Address Configuration Options in its Configure-Request packets. An implementation receiving a Configure-Request specifying multiple IP Address Configuration Options may send a Configure-Reject specifying one or more of the specified IP Addresses. An implementation which desires that no IP addresses be assigned (such as a "half-gateway") may reject all IP Address Configuration Options. A summary of the IP-Addresses 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 | Source-IP-Address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Source-IP-Address (cont) | Destination-IP-Address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Destination-IP-Address (cont) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 1 Length 10 Source-IP-Address The four octet Source-IP-Address is the desired local address of the sender of a Configure-Request. In a Configure-Ack, Configure-Nak or Configure-Reject, the Source-IP-Address is the remote address of the sender, and is thus a local address with respect to the Configuration Option receiver. McGregor [Page 5] Internet Draft PPP IPCP August 1991 Destination-IP-Address The four octet Destination-IP-Address is the remote address with respect to the sender of a Configure-Request. In a Configure-Ack, Configure-Nak or Configure-Reject, the Destination-IP-Address is the local address of the sender, and is thus a remote address with respect to the Configuration Option receiver. Default No IP addresses assigned. McGregor [Page 6] Internet Draft PPP IPCP August 1991 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 [Page 7] Internet Draft PPP IPCP August 1991 Default No compression protocol enabled. McGregor [Page 8] Internet Draft PPP IPCP August 1991 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 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 [Page 9] Internet Draft PPP IPCP August 1991 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]. 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 [Page 10] Internet Draft PPP IPCP August 1991 A. IPCP event cookbook The following pseudo-code represents a suggested approach to implementing the linkage between the LCP and the IPCP events. 1) The administrator initiates an Open IP command: If PPP is in Network-Layer Phase, then send an ActiveOpen event to IPCP; else send a PassiveOpen event to IPCP. 2) The administrator initiates a Close IP command: Send the Close event to IPCP. 3) Transition into Network-Layer Phase: If IPCP is not in Closed state, then send an ActiveOpen event to IPCP. 4) Transition out of Network-Layer Phase: Send a Down event to IPCP. B. IPCP Recommended Options The following Configurations Options are recommended: IP-Addresses -- only on dial-up lines. IP-Compression-Protocol -- with at least 4 slots, usually 16 slots. McGregor [Page 11] Internet Draft PPP IPCP August 1991 References [1] Simpson, W. A., "The Point-to-Point Protocol for the Transmission of Multi-Protocol of Datagrams Over Point-to-Point Links", 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., and J. Postel, "Assigned Numbers", RFC 1060, USC/Information Sciences Institute, March 1990. Security Considerations Security issues are not discussed in this memo. Acknowledgments Some of the text in this document is taken from previous documents produced by the Point-to-Point Protocol Working Group of the Internet Engineering Task Force (IETF), formerly chaired by Drew Perkins of Carnegie Mellon University, by Russ Hobby of the University of California at Davis, and by Steve Knowles of FTP Software. Editted and formatted by Bill Simpson. Chair's Address The working group can be contacted via the current chair: Brian Lloyd Telebit Corporation 1315 Chesapeake Terrace Sunnyvale, CA 94089-1100 McGregor [Page 12] Internet Draft PPP IPCP August 1991 Phone: (408) 745-3103 EMail: brian@telebit.com Author's Address Questions about this memo can also be directed to: Glenn McGregor Merit Network, Inc. 1075 Beal Avenue Ann Arbor, MI 48109-2099 Phone: (313) 763-1203 EMail: ghm@merit.edu McGregor [Page 13]