GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc1332

Network Working Group G. McGregor Request for Comments: 1332 Merit Obsoletes: 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 1992

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 .........................    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 .............................................   12

McGregor [Page ii] RFC 1332 PPP IPCP May 1992

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 [Page 1] RFC 1332 PPP IPCP May 1992

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 [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 1992

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 [Page 4] RFC 1332 PPP IPCP May 1992

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 [Page 5] RFC 1332 PPP IPCP May 1992

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 6] RFC 1332 PPP IPCP May 1992

 Default
    No compression protocol enabled.

McGregor [Page 7] RFC 1332 PPP IPCP May 1992

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 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
    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
 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 [Page 8] RFC 1332 PPP IPCP May 1992

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 [Page 9] RFC 1332 PPP IPCP May 1992

 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 [Page 10] RFC 1332 PPP IPCP May 1992

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, November
       1983.
 [5]   Mogul, J., and S. Deering, "Path MTU Discovery", RFC 1191,
       November 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.

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 [Page 11] RFC 1332 PPP IPCP May 1992

 Bill Simpson helped with the document formatting.

Chair's Address

 The working group can be contacted via the current chair:
    Brian Lloyd
    Lloyd & Associates
    3420 Sudbury Road
    Cameron Park, California 95682
    Phone: (916) 676-1147
    EMail: brian@ray.lloyd.com

Author's Address

 Questions about this memo can also be directed to:
    Glenn McGregor
    Merit Network, Inc.
    1071 Beal Avenue
    Ann Arbor, MI 48109-2103
    Phone: (313) 763-1203
    EMail: Glenn.McGregor@Merit.edu

McGregor [Page 12]

/data/webs/external/dokuwiki/data/pages/rfc/rfc1332.txt · Last modified: 1992/05/22 23:21 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki