computer networking A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ma ...

, Internet Protocol Control Protocol (IPCP) is a Network Control Protocol (NCP) for establishing and configuring

Internet Protocol The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. IP h ...

over a Point-to-Point Protocol link. IPCP is responsible for configuring the IP addresses as well as for enabling and disabling the IP protocol modules on both ends of the point-to-point link. IPCP uses the same packet exchange mechanism as the

Link Control Protocol In computer networking, the Link Control Protocol (LCP) forms part of the Point-to-Point Protocol (PPP), within the family of Internet protocols. In setting up PPP communications, both the sending and receiving devices send out LCP packets to dete ...

. IPCP packets may not be exchanged until PPP has reached the Network-Layer Protocol phase, and any IPCP packets received before this phase is reached should be silently discarded. IPCP has the NCP protocol code number 0x8021. Each of the two endpoints of a PPP connection must send an IPCP configure request to its peer because the TCP/IP options are independent for each direction of a PPP connection. A PPP endpoint can request a specific IP address from its peer. It can also ask the peer to suggest an IP address by requesting the address 0.0.0.0; the peer then sends its suggestion in an IPCP Nak packet, which the first peer must subsequently request in order to complete the negotiation. In practice, in protocols like

PPPoE The Point-to-Point Protocol over Ethernet (PPPoE) is a network protocol for encapsulating Point-to-Point Protocol (PPP) frames inside Ethernet frames. It appeared in 1999, in the context of the boom of DSL as the solution for tunneling packet ...

which is commonly used in home broadband connections, the latter method (request suggestion, nak with suggestion, request suggested address) is used to set the IP address of the

ISP An Internet service provider (ISP) is an organization that provides services for accessing, using, or participating in the Internet. ISPs can be organized in various forms, such as commercial, community-owned, non-profit, or otherwise private ...

's client endpoint (i.e. the

customer-premises equipment In telecommunications, a customer-premises equipment or customer-provided equipment (CPE) is any terminal and associated equipment located at a subscriber's premises and connected with a carrier's telecommunication circuit at the demarcation poi ...

), while the former method (request address) is used to inform the client of the ISP endpoint IP ( provider edge equipment). A similar NCP, the

IPv6 Control Protocol Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. IPv ...

exists for

IPv6 Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communication protocol, communications protocol that provides an identification and location system for computers on networks and routes traffic ...

. It can be used together with IPCP on the same PPP connection for a

dual stack Internet Protocol version 6 (IPv6) is the most recent version of the Internet Protocol (IP), the communications protocol that provides an identification and location system for computers on networks and routes traffic across the Internet. IPv ...

link. (When interfacing newer and older equipment that doesn't support IPv6 one sees LCP ProtRej messages for protocol 0x8057 from the side that doesn't support IPV6CP.)

IP Frame

After the configuration is done, the link is able to carry IP data as a payload of the PPP frame. This code indicates that IP data is being carried. IPCP header: Code. 8 bits.
Specifies the function to be performed. Identifier. 8 bits. Used to match requests and replies. Length. 16 bits.
Size of the packet including the header. Data. Variable length.
Zero or more bytes of data as indicated by the Length. This field may contain one or more ''Options''.

Configuration Options

IPCP Configuration Options allow negotiatiation of desirable Internet Protocol parameters. IPCP uses the same Configuration Option format defined for LCP

, with a separate set of Options. IPCP Configuration Options: Option. 8 bits. Length. 8 bits. Data. Variable length.

IP-Compression-Protocol

IP-Address

Microsoft

In the Microsoft implementation, "Common IPCP options include an IP address and the IP addresses of

DNS The Domain Name System (DNS) is a hierarchical and distributed naming system for computers, services, and other resources in the Internet or other Internet Protocol (IP) networks. It associates various information with domain names assigned to ...

and

NetBIOS NetBIOS () is an acronym for Network Basic Input/Output System. It provides services related to the session layer of the OSI model allowing applications on separate computers to communicate over a local area network. As strictly an API, NetB ...

name servers."

References

*: The Internet Protocol Control Protocol (IPCP) *: PPP