Misplaced Pages

#55944

34-458: PPP is used over many types of physical networks, including serial cable , phone line , trunk line , cellular telephone , specialized radio links, ISDN , and fiber optic links such as SONET . Since IP packets cannot be transmitted over a modem line on their own without some data link protocol that can identify where the transmitted frame starts and where it ends, Internet service providers (ISPs) have used PPP for customer dial-up access to

68-425: A checksum to detect transmission errors. PPP on serial links is usually encapsulated in a framing similar to HDLC , described by IETF RFC 1662. The Flag field is present when PPP with HDLC-like framing is used. The Address and Control fields always have the value hex FF (for "all stations") and hex 03 (for "unnumbered information"), and can be omitted whenever PPP LCP Address-and-Control-Field-Compression (ACFC)

102-645: A transport layer protocol, comparable with the User Datagram Protocol (UDP) in the Internet protocol suite . The IPX network number is conceptually identical to the network part of the IP address (the parts with netmask bits set to 1); the node number has the same meaning as the bits of IP address with netmask bits set to 0. The difference is that the boundary between network and node part of address in IP

136-480: A basic PPP connection has to be established before LCP is able to configure it. RFC 1994 describes Challenge-Handshake Authentication Protocol (CHAP), which is preferred for establishing dial-up connections with ISPs. Although deprecated, Password Authentication Protocol (PAP) is still sometimes used. Another option for authentication over PPP is Extensible Authentication Protocol (EAP) described in RFC 2284. After

170-538: A capacitive load of 2500 pF. This does not correspond to a fixed length of cable since varying cables have different characteristics. Empirically tested combinations of bit rate, serial ports, cable type, and lengths may provide reliable communications, but generally RS-232-compatible ports are intended to be connected by, at the most, a few tens of metres of cable. Other serial communications standards are better adapted to drive hundreds or thousands of metres of cable. IPX Internetwork Packet Exchange ( IPX )

204-399: A home computer to an Internet Service Provider using two traditional 56k modems, or to connect a company through two leased lines. On a single PPP line frames cannot arrive out of order, but this is possible when the frames are divided among multiple PPP connections. Therefore, Multilink PPP must number the fragments so they can be put in the right order again when they arrive. Multilink PPP

238-488: A variable length with a negotiated maximum called the Maximum Transmission Unit . By default, the maximum is 1500 octets . It might be padded on transmission; if the information for a particular protocol can be padded, that protocol must allow information to be distinguished from padding. PPP frames are encapsulated in a lower-layer protocol that provides framing and may provide other functions such as

272-465: Is 16 bits - Polynomial x + x + x + 1). The FCS is calculated over the Address, Control, Protocol, Information and Padding fields after the message has been encapsulated. Multilink PPP (also referred to as MLPPP , MP , MPPP , MLP , or Multilink) provides a method for spreading traffic across multiple distinct PPP connections. It is defined in RFC 1990. It can be used, for example, to connect

306-406: Is a full Internet connection over telephone lines via modem. It is more reliable than SLIP because it double checks to ensure Internet packets arrive intact. It resends any damaged packets. PPP was designed somewhat after the original HDLC specifications. The people who had designed PPP included many additional features that had been seen only in proprietary data-link protocols up to that time. PPP

340-500: Is a layered protocol that has three components: LCP initiates and terminates connections gracefully, allowing hosts to negotiate connection options. It is an integral part of PPP, and is defined in the same standard specification. LCP provides automatic configuration of the interfaces at each end (such as setting datagram size, escaped characters, and magic numbers) and for selecting optional authentication. The LCP protocol runs on top of PPP (with PPP protocol number 0xC021) and therefore

374-526: Is an example of a link aggregation technology. Cisco IOS Release 11.1 and later supports Multilink PPP. With PPP, one cannot establish several simultaneous distinct PPP connections over a single link. That's not possible with Multilink PPP either. Multilink PPP uses contiguous numbers for all the fragments of a packet, and as a consequence it is not possible to suspend the sending of a sequence of fragments of one packet in order to send another packet. This prevents from running Multilink PPP multiple times on

SECTION 10

#1732776481056

408-513: Is negotiated. The frame check sequence (FCS) field is used for determining whether an individual frame has an error. It contains a checksum computed over the frame to provide basic protection against errors in transmission. This is a CRC code similar to the one used for other layer two protocol error protection schemes such as the one used in Ethernet. According to RFC 1662, it can be either 16 bits (2 bytes) or 32 bits (4 bytes) in size (default

442-405: Is possible, but it works similarly as if separate cabling systems were used (i.e. different network numbers must be used for different frame formats even in the same cabling system and a router must be used to allow communication between nodes using different frame formats in the same cabling system). The node number is used to address an individual computer (or more exactly, a network interface) in

476-504: Is specified in IP routing tables. There are three routing protocols available for IPX networks. In early IPX networks, a version of Routing Information Protocol (RIP) was the only available protocol to exchange routing information. Unlike RIP for IP , it uses delay time as the main metric, retaining the hop count as a secondary metric. Since NetWare 3, the NetWare Link Services Protocol (NLSP) based on IS-IS

510-485: Is specified in RFC 1661. RFC 2516 describes Point-to-Point Protocol over Ethernet (PPPoE) as a method for transmitting PPP over Ethernet that is sometimes used with DSL . RFC 2364 describes Point-to-Point Protocol over ATM (PPPoA) as a method for transmitting PPP over ATM Adaptation Layer 5 ( AAL5 ), which is also a common alternative to PPPoE used with DSL. PPP, PPPoE and PPPoA are widely used in WAN lines. PPP

544-508: Is the network-layer protocol in the IPX/SPX protocol suite . IPX is derived from Xerox Network Systems ' IDP . It also has the ability to act as a transport layer protocol. The IPX/SPX protocol suite was very popular through the late 1980s and mid-1990s because it was used by Novell NetWare , a network operating system . Due to Novell NetWare's popularity, IPX became a prominent protocol for internetworking . A big advantage of IPX

578-601: Is variable, while in IPX it is fixed. As the node address is usually identical to the MAC address of the network adapter, the Address Resolution Protocol is not needed in IPX. For routing , the entries in the IPX routing table are similar to IP routing tables; routing is done by network address, and for each network address a network:node of the next router is specified in a similar fashion an IP address/netmask

612-467: The Internet . PPP is used on former dial-up networking lines. Two derivatives of PPP, Point-to-Point Protocol over Ethernet (PPPoE) and Point-to-Point Protocol over ATM (PPPoA), are used most commonly by ISPs to establish a digital subscriber line (DSL) Internet service LP connection with customers. PPP is very commonly used as a data-link-layer protocol for connection over synchronous and asynchronous circuits , where it has largely superseded

646-471: The MAC address of its network card as the node address and learns what it needs to know about the network topology from the servers or routers – routes are propagated by Routing Information Protocol , services by Service Advertising Protocol . A small IPX network administrator had to care only Each IPX packet begins with a header with the following structure: The Packet Type values are: An IPX address has

680-448: The 0x00 byte can be omitted. The Protocol field indicates the type of payload packet: 0xC021 for LCP , 0x80xy for various NCPs , 0x0021 for IP, 0x0029 AppleTalk, 0x002B for IPX , 0x003D for Multilink, 0x003F for NetBIOS , 0x00FD for MPPC and MPPE , etc. PPP is limited, and cannot contain general Layer 3 data, unlike EtherType . The Information field contains the PPP payload; it has

714-487: The connection has been established. For example, IP uses IPCP, and Internetwork Packet Exchange (IPX) uses the Novell IPX Control Protocol ( IPX/SPX ). NCPs include fields containing standardized codes to indicate the network layer protocol type that the PPP connection encapsulates. The following NCPs may be used with PPP: PPP detects looped links using a feature involving magic numbers . When

SECTION 20

#1732776481056

748-400: The dominant layer-3 protocol. PPP permits multiple network layer protocols to operate on the same communication link. For every network layer protocol used, a separate Network Control Protocol ( NCP ) is provided in order to encapsulate and negotiate options for the multiple network layer protocols. It negotiates network-layer information, e.g. network address or compression options, after

782-638: The following structure: The network number allows to address (and communicate with) the IPX nodes which do not belong to the same network or cabling system . The cabling system is a network in which a data link layer protocol can be used for communication. To allow communication between different networks, they must be connected with IPX routers . A set of interconnected networks is called an internetwork . Any Novell NetWare server may serve as an IPX router. Novell also supplied stand-alone routers. Multiprotocol routers of other vendors often support IPX routing. Using different frame formats in one cabling system

816-467: The impression of direct physical connections between the tunnel endpoints. On a Linux host for example, these interfaces would be called tun0 or ppp0 . As there are only two endpoints on a tunnel, the tunnel is a point-to-point connection and PPP is a natural choice as a data link layer protocol between the virtual network interfaces. PPP can assign IP addresses to these virtual interfaces, and these IP addresses can be used, for example, to route between

850-501: The link has been established, additional network ( layer 3 ) configuration may take place. Most commonly, the Internet Protocol Control Protocol (IPCP) is used, although Internetwork Packet Exchange Control Protocol (IPXCP) and AppleTalk Control Protocol (ATCP) were once popular. Internet Protocol Version 6 Control Protocol (IPv6CP) will see extended use in the future, when IPv6 replaces IPv4 as

884-514: The need for PPP and its development. A series of related RFCs have been written to define how a variety of network control protocols, including TCP/IP , DECnet , AppleTalk , IPX , work with PPP; they can be found on the Datatracker IETF website. Serial cable A serial cable or RS-232 cable is a cable used to transfer information between two devices using a serial communication protocol. The form of connectors depends on

918-403: The network. Client stations use its network interface card MAC address as the node number. The value FF:FF:FF:FF:FF:FF may be used as a node number in a destination address to broadcast a packet to "all nodes in the current network". The socket number serves to select a process or application in the destination node. The presence of a socket number in the IPX address allows the IPX to act as

952-610: The networks on both sides of the tunnel. IPsec in tunneling mode does not create virtual physical interfaces at the end of the tunnel, since the tunnel is handled directly by the TCP/IP stack. L2TP can be used to provide these interfaces, this technique is called L2TP/IPsec. In this case too, PPP provides IP addresses to the extremities of the tunnel. PPP is defined in RFC 1661 (The Point-to-Point Protocol, July 1994). RFC 1547 (Requirements for an Internet Standard Point-to-Point Protocol, December 1993) provides historical information about

986-582: The node sends PPP LCP messages, these messages may include a magic number. If a line is looped, the node receives an LCP message with its own magic number, instead of getting a message with the peer's magic number. The previous section introduced the use of LCP options to meet specific WAN connection requirements. PPP may include the following LCP options: PPP frames are variants of HDLC frames: If both peers agree to Address field and Control field compression during LCP, then those fields are omitted. Likewise if both peers agree to Protocol field compression, then

1020-443: The older Serial Line Internet Protocol (SLIP) and telephone company mandated standards (such as Link Access Protocol, Balanced (LAPB) in the X.25 protocol suite). The only requirement for PPP is that the circuit provided be duplex . PPP was made to work with numerous network-layer protocols , including Internet Protocol (IP), TRILL , Novell's Internetwork Packet Exchange (IPX), NBF , DECnet and AppleTalk . Like SLIP, this

1054-424: The particular serial port used. A cable wired for connecting two DTEs directly is known as a null modem cable. The maximum working length of a cable varies depending on the characteristics of the transmitters and receivers, the baud rate on the cable, and the capacitance and electrical impedance of the cable. The RS-232 standard states that a compliant port must provide defined signal characteristics for

Point-to-Point Protocol - Misplaced Pages Continue

1088-484: The same links. Multiclass PPP is a kind of Multilink PPP where each "class" of traffic uses a separate sequence number space and reassembly buffer. Multiclass PPP is defined in RFC 2686 PPTP (Point-to-Point Tunneling Protocol) is a form of PPP between two hosts via GRE using encryption ( MPPE ) and compression ( MPPC ). Many protocols can be used to tunnel data over IP networks. Some of them, like SSL , SSH , or L2TP create virtual network interfaces and give

1122-604: Was a small memory footprint of the IPX driver, which was vital for DOS and Windows up to Windows 95 due to the limited size at that time of conventional memory . Another IPX advantage was easy configuration of its client computers. However, IPX does not scale well for large networks such as the Internet. As such, IPX usage decreased as the boom of the Internet made TCP/IP nearly universal. Computers and networks can run multiple network protocols , so almost all IPX sites also ran TCP/IP, to allow Internet connectivity. It

1156-519: Was also possible to run later Novell products without IPX, with the beginning of full support for both IPX and TCP/IP by NetWare version 5 in late 1998. A big advantage of IPX protocol is its little or no need for configuration. In the time when protocols for dynamic host configuration did not exist and the BOOTP protocol for centralized assigning of addresses was not common, the IPX network could be configured almost automatically. A client computer uses

#55944