| Point-to-Point Protocol, or PPP, is a data link protocol | | | | After the link has been established, additional |
| commonly used to establish a direct connection | | | | network (layer 3) configuration may take place. Most |
| between two networking nodes. It can provide | | | | commonly, the Internet Protocol Control Protocol |
| connection authentication, transmission encryption | | | | (IPCP) is used, although Internetwork Packet |
| privacy, and compression. | | | | Exchange Control Protocol (IPXCP) and AppleTalk |
| PPP is used over many types of physical networks | | | | Control Protocol (ATCP) were once very popular. |
| including serial cable, phone line, trunk line, cellular | | | | Internet Protocol Version 6 Control Protocol (IPv6CP) |
| telephone, specialized radio links, and fiber optic links | | | | will see extended use in the future, when IPv6 |
| such as SONET. Most Internet service providers | | | | replaces IPv4's position as the dominant layer-3 |
| (ISPs) use PPP for customer dial-up access to the | | | | protocol. |
| Internet. Two encapsulated forms of PPP, | | | | Multiple network layer protocols |
| Point-to-Point Protocol over Ethernet (PPPoE) and | | | | PPP permits multiple network layer protocols to |
| Point-to-Point Protocol over ATM (PPPoA), are used | | | | operate on the same communication link. For every |
| by Internet Service Providers (ISPs) to connect | | | | network layer protocol used, a separate Network |
| Digital Subscriber Line (DSL) Internet service. | | | | Control Protocol (NCP) is provided in order to |
| PPP is commonly used as a data link layer protocol | | | | encapsulate and negotiate options for the multiple |
| for connection over synchronous and asynchronous | | | | network layer protocols. |
| circuits, where it has largely superseded the older, | | | | For example, Internet Protocol (IP) uses the IP |
| non-standard Serial Line Internet Protocol (SLIP) and | | | | Control Protocol (IPCP), and Internetwork Packet |
| telephone company mandated standards (such as | | | | Exchange (IPX) uses the Novell IPX Control Protocol |
| Link Access Protocol, Balanced (LAPB) in the X.25 | | | | (IPXCP). Read more at <a rel="nofollow" |
| protocol suite). Read more at <a rel="nofollow" | | | | onclick="javascript:_gaq.push(['_trackPageview', ' |
| onclick="javascript:_gaq.push(['_trackPageview', ' | | | | outgoing/article_exit_link']);" href=" point out |
| outgoing/article_exit_link']);" href=" out< | | | | site</a>.NCPs include fields containing |
| a> PPP was designed to work with numerous | | | | standardized codes to indicate the network layer |
| network layer protocols, including Internet Protocol | | | | protocol type that the PPP connection encapsulates. |
| (IP), Novell's Internetwork Packet Exchange (IPX), | | | | PPP Configuration Options |
| NBF and AppleTalk.More about this protocol at <a | | | | The previous section introduced the use of LCP |
| rel="nofollow" | | | | options to meet specific WAN connection |
| onclick="javascript:_gaq.push(['_trackPageview', ' | | | | requirements. PPP may include the following LCP |
| outgoing/article_exit_link']);" href=" point out | | | | options: |
| site</a>. | | | | Authentication - Peer routers exchange authentication |
| PPP is also used over broadband connections. RFC | | | | messages. Two authentication choices are Password |
| 2516 describes Point-to-Point Protocol over Ethernet | | | | Authentication Protocol (PAP) and Challenge |
| (PPPoE), a method for transmitting PPP over | | | | Handshake Authentication Protocol (CHAP). |
| Ethernet that is sometimes used with DSL. RFC 2364 | | | | Authentication is explained in the next section. |
| describes Point-to-Point Protocol over ATM (PPPoA), | | | | Compression - Increases the effective throughput on |
| a method for transmitting PPP over ATM Adaptation | | | | PPP connections by reducing the amount of data in |
| Layer 5 (AAL5), which is also sometimes used with | | | | the frame that must travel across the link. The |
| DSL. | | | | protocol decompresses the frame at its destination. |
| Automatic self configuration | | | | Two compression protocols available in Cisco routers |
| Link Control Protocol (LCP) is an integral part of PPP, | | | | are Stacker and Predictor. |
| and is defined in the same standard specification. LCP | | | | Error detection - Identifies fault conditions. The |
| provides automatic configuration of the interfaces at | | | | Quality and Magic Number options help ensure a |
| each end (such as setting datagram size, escaped | | | | reliable, loop-free data link. The Magic Number field |
| characters, and magic numbers) and for selecting | | | | helps in detecting links that are in a looped-back |
| optional authentication. The LCP protocol runs on top | | | | condition. Until the Magic-Number Configuration Option |
| of PPP (with PPP protocol number 0xC021) and | | | | has been successfully negotiated, the Magic-Number |
| therefore a basic PPP connection has to be | | | | must be transmitted as zero. Magic numbers are |
| established before LCP is able to configure it. | | | | generated randomly at each end of the connection. |
| RFC 1994 describes Challenge-handshake | | | | Multilink - Cisco IOS Release 11.1 and later supports |
| authentication protocol (CHAP), which is preferred for | | | | multilink PPP. This alternative provides load balancing |
| establishing dial-up connections with ISPs. Although | | | | over the router interfaces that PPP uses. Multilink PPP |
| deprecated,Password authentication protocol (PAP) is | | | | (also referred to as MLPPP, MP, MPPP, MLP, or |
| still sometimes used. | | | | Multilink) provides a method for spreading traffic |
| Another option for authentication over PPP is | | | | across multiple distinct PPP connections. |
| Extensible Authentication Protocol (EAP). | | | | |