HTTP/1.1 200 OK Date: Tue, 09 Apr 2002 06:39:01 GMT Server: Apache/1.3.20 (Unix) Last-Modified: Thu, 02 Feb 1995 23:00:00 GMT ETag: "304d77-4e7e-2f3163f0" Accept-Ranges: bytes Content-Length: 20094 Connection: close Content-Type: text/plain Network Working Group Glenn McGregor INTERNET DRAFT Lloyd Internetworking Obsoletes: RFC 1332 Gurdeep Singh Pall Microsoft Corporation Dec 1994 The PPP Internet Protocol Control Protocol (IPCP) Status of this Memo This RFC specifies an IAB standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "IAB Official Protocol Standards" 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 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. This document is a product of the Point-to-Point Protocol Working Group of the Internet Engineering Task Force (IETF). McGregor & Pall [Page i] INTERNET DRAFT PPP IPCP Dec 1994 Table of Contents 1. Introduction .......................................... 1 2. A PPP Network Control Protocol (NCP) for IP ........... 2 2.1 Sending IP Datagrams ............................ 3 3. IPCP Configuration Options ............................ 4 3.1 IP-Compression-Protocol ......................... 5 3.2 IP-Address ...................................... 7 3.3 IP-Broadcast-Forwarding .......................... 9 4. Van Jacobson TCP/IP header compression ................ 11 4.1 Configuration Option Format ..................... 11 APPENDICES ................................................... 13 A. IPCP Recommended Options .............................. 13 SECURITY CONSIDERATIONS ...................................... 13 REFERENCES ................................................... 13 ACKNOWLEDGEMENTS ............................................. 14 CHAIR'S ADDRESS .............................................. 14 AUTHOR'S ADDRESS ............................................. 14 McGregor & Pall [Page ii] INTERNET DRAFT PPP IPCP Dec 1994 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 & Pall [Page 1] INTERNET DRAFT PPP IPCP Dec 1994 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. McGregor & Pall [Page 2] INTERNET DRAFT PPP IPCP Dec 1994 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). 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 & Pall [Page 3] INTERNET DRAFT PPP IPCP Dec 1994 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 Reserved 2 IP-Compression-Protocol 3 IP-Address 4 IP-Broadcast-Forwarding McGregor & Pall [Page 4] INTERNET DRAFT PPP IPCP Dec 1994 3.1. 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 McGregor & Pall [Page 5] INTERNET DRAFT PPP IPCP Dec 1994 Data The Data field is zero or more octets and contains additional data as determined by the particular compression protocol. Default No compression protocol enabled. McGregor & Pall [Page 6] INTERNET DRAFT PPP IPCP Dec 1994 3.2. 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 state which IP-address is desired, or to request that the peer provide the information. The peer can provide this information by NAKing the option, and returning a valid IP-address. 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 the IP-address value must be 0.0.0.0 to indicate a request that the peer provide the information. It is valid for a peer to send a Configure-Request with an IP-address value of 0.0.0.0 to indicate that it does not know the IP-address of its end of the link. The only valid responses to this Configure-Request are: Configure-Ack with IP-address of 0.0.0.0, meaning that the responding peer does not know the IP-address either. Configure-Nak with a valid IP-address, meaning that the responding peer is returning an IP-address that can be used. It is valid for a peer to send a Configure-Request with an IP-address value other than 0.0.0.0 to indicate that it knows the IP-address of its end of the link. The only valid response to this Configure-Request are: Configure-Ack with the requested IP-address, meaning that the responding peer agrees with the IP-address requested. Configure-Nak with an IP-address of 0.0.0.0, meaning that the responding peer does not care about the IP-address used by the requesting peer. Configure-Nak with a valid IP-address that is different from the one requested, meaning that the responding peer does not want the requesting peer to use the IP-address specified in the Configure-Request, and that it wants the peer to use the specified IP-address instead. McGregor & Pall [Page 7] INTERNET DRAFT PPP IPCP Dec 1994 It is valid for a peer not to send a Configure-Request for this option at all, meaning that it does not want to inform the peer of its IP-address. 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 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 & Pall [Page 8] INTERNET DRAFT PPP IPCP Dec 1994 3.3. IP-Broadcast-Forwarding Description This Configuration Option provides a way for the sending peer to request forwarding of IP Broadcast packets (sent to IP-address of 255.255.255.255), IP Network Broadcast packets (sent to IP-address of x.255.255.255 for network x.0.0.0), and IP Sub-network Broadcast packets (sent to IP-address x.y.255.255 for sub-network x.y.0.0). It allows the sender of the Configure-Request to state which type of broadcasts it is requesting to be forwarded by the peer. The peer should respond by ACKing the option if it supports forwarding of types of broadcasts requested. Else it should NAK the option returning which of the requested types of broadcasts it supports. This document does not define the basis for forwarding of Broadcast packets by the peer. By default, broadcast packets are not forwarded by the peer. A summary of the IP-Broadcast-Forwarding 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 | Broadcast Type| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Type 4 Length 3 IP-Compression-Protocol Broadcast Type: Value (in hex) 00 No Broadcast forwarding requested (default) 01 IP Broadcast forwarding requested 02 IP Network Broadcast forwarding requested 04 IP Sub-Network Broadcast forwarding requested. McGregor & Pall [Page 9] INTERNET DRAFT PPP IPCP Dec 1994 Default No Broadcast forwarding enabled. McGregor & Pall [Page 10] INTERNET DRAFT PPP IPCP Dec 1994 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 separately 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 & Pall [Page 11] INTERNET DRAFT PPP IPCP Dec 1994 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 & Pall [Page 12] INTERNET DRAFT PPP IPCP Dec 1994 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., "The Point-to-Point Protocol", RFC 1331, May 1992. [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, December 1983. [5] Mogul, J., and S. Deering, "Path MTU Discovery", RFC 1191, December 1990. [6] Reynolds, J., and J. Postel, "Assigned Numbers", RFC 1060, USC/Information Sciences Institute, March 1990. [7] Perkins, D., and R. Hobby, "Point-to-Point Protocol (PPP) initial configuration options", RFC 1172, August 1990. [8] Mogul, J., "Broadcasting Internet Datagrams", RFC 919, October 1984. McGregor & Pall [Page 13] INTERNET DRAFT PPP IPCP Dec 1994 Acknowledgments Some of the text in this document is taken from RFCs 1332, by Glenn McGregor of Merit Network. Steve Cobb of Microsoft Corporation has contributed in making the IP-Address Option description more specific based on implementation experience. Information leading to the expanded IP-Compression option provided by Van Jacobson at SIGCOMM '90. Chair's Address The working group can be contacted via the current chair: Fred Baker EMail: fred@cisco.com Authors Address Questions about this memo can also be directed to: Glenn McGregor Lloyd Internetworking 3031 Alhambra Drive Cameron Park, CA 95682 Phone: (916) 676 1147 Email: glenn@lloyd.com Gurdeep Singh Pall Microsoft Corporation 1 Microsoft Way, Redmond WA 98052 Phone: (206) 882 8080 EMail: gurdeep@microsoft.com McGregor & Pall [Page 14]