Network Working Group                                        G. McGregorRequest for Comments: 1332                                         MeritObsoletes: RFC 1172                                             May 1992           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 RFC is a product of the Point-to-Point Protocol Working Group of   the Internet Engineering Task Force (IETF).McGregor                                                        [Page i]RFC 1332                        PPP IPCP                        May 1992Table 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 .........................    6        3.3       IP-Address ......................................    8     4.     Van Jacobson TCP/IP header compression ................    9        4.1       Configuration Option Format .....................    9     APPENDICES ...................................................   11     A.     IPCP Recommended Options ..............................   11     SECURITY CONSIDERATIONS ......................................   11     REFERENCES ...................................................   11     ACKNOWLEDGEMENTS .............................................   11     CHAIR'S ADDRESS ..............................................   12     AUTHOR'S ADDRESS .............................................   12McGregor                                                       [Page ii]RFC 1332                        PPP IPCP                        May 19921.  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                                                        [Page 1]RFC 1332                        PPP IPCP                        May 19922.  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                                                        [Page 2]RFC 1332                        PPP IPCP                        May 1992   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]RFC 1332                        PPP IPCP                        May 19923.  IPCP Configuration OptionsIPCP Configuration Options allow negotiatiation of desirable InternetProtocol parameters.  IPCP uses the same Configuration Option formatdefined for LCP [1], with a separate set of Options.The most up-to-date values of the IPCP Option Type field are specifiedin the most recent "Assigned Numbers" RFC [6].  Current values areassigned as follows:   1       IP-Addresses   2       IP-Compression-Protocol   3       IP-AddressMcGregor                                                        [Page 4]RFC 1332                        PPP IPCP                        May 19923.1.  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                                                        [Page 5]