Internet RFC/STD/FYI/BCP Archives
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).
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
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).
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.
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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]. 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 |
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.
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