TCPIP tutorial RFC 1180.docx

1、TCPIP tutorial RFC 1180TCP/IP tutorialRFC 1180 Document IESG Evaluation Record IESG Writeups History Document type:RFC - Informational (Legacy Stream) Errata Published:1991-01Other versions:plain text, pdf, html IPR Disclosures | Dependencies to this RFC Network Working Group T. SocolofskyRequest fo

2、r Comments: 1180 C. Kale Spider Systems Limited January 1991 A TCP/IP TutorialStatus of this Memo This RFC is a tutorial on the TCP/IP protocol suite, focusing particularly on the steps in forwarding an IP datagram from source host to destination host through a router. It does not specify an Interne

3、t standard. Distribution of this memo is unlimited.Table of Contents 1. Introduction. 1 2. TCP/IP Overview. 2 3. Ethernet. 8 4. ARP. 9 5. Internet Protocol. 12 6. User Datagram Protocol. 22 7. Transmission Control Protocol. 24 8. Network Applications. 25 9. Other Information. 27 10. References. 27 1

4、1. Relation to other RFCs. 27 12. Security Considerations. 27 13. Authors Addresses. 281. Introduction This tutorial contains only one view of the salient points of TCP/IP, and therefore it is the bare bones of TCP/IP technology. It omits the history of development and funding, the business case for

5、 its use, and its future as compared to ISO OSI. Indeed, a great deal of technical information is also omitted. What remains is a minimum of information that must be understood by the professional working in a TCP/IP environment. These professionals include the systems administrator, the systems pro

6、grammer, and the network manager. This tutorial uses examples from the UNIX TCP/IP environment, however the main points apply across all implementations of TCP/IP. Note that the purpose of this memo is explanation, not definition. If any question arises about the correct specification of a protocol,

7、 please refer to the actual standards defining RFC.Socolofsky & Kale Page 1RFC 1180 A TCP/IP Tutorial January 1991 The next section is an overview of TCP/IP, followed by detailed descriptions of individual components.2. TCP/IP Overview The generic term TCP/IP usually means anything and everything re

8、lated to the specific protocols of TCP and IP. It can include other protocols, applications, and even the network medium. A sample of these protocols are: UDP, ARP, and ICMP. A sample of these applications are: TELNET, FTP, and rcp. A more accurate term is internet technology. A network that uses in

9、ternet technology is called an internet.2.1 Basic Structure To understand this technology you must first understand the following logical structure: - | network applications | | | |. | / . | / .| | - - | | |TCP| |UDP| | | - - | | / | | - | | | IP | | | - -*- | | |ARP| | | | - | | | | | | - | | |ENET

10、| | | - | -|- | -o- Ethernet Cable Figure 1. Basic TCP/IP Network Node This is the logical structure of the layered protocols inside a computer on an internet. Each computer that can communicate using internet technology has such a logical structure. It is this logical structure that determines the

11、behavior of the computer on the internet. The boxes represent processing of the data as it passes through the computer, and the lines connecting boxes show the path ofSocolofsky & Kale Page 2RFC 1180 A TCP/IP Tutorial January 1991 data. The horizontal line at the bottom represents the Ethernet cable

12、; the o is the transceiver. The * is the IP address and the is the Ethernet address. Understanding this logical structure is essential to understanding internet technology; it is referred to throughout this tutorial.2.2 Terminology The name of a unit of data that flows through an internet is depende

13、nt upon where it exists in the protocol stack. In summary: if it is on an Ethernet it is called an Ethernet frame; if it is between the Ethernet driver and the IP module it is called a IP packet; if it is between the IP module and the UDP module it is called a UDP datagram; if it is between the IP m

14、odule and the TCP module it is called a TCP segment (more generally, a transport message); and if it is in a network application it is called a application message. These definitions are imperfect. Actual definitions vary from one publication to the next. More specific definitions can be found in RF

15、C 1122, section 1.3.3. A driver is software that communicates directly with the network interface hardware. A module is software that communicates with a driver, with network applications, or with another module. The terms driver, module, Ethernet frame, IP packet, UDP datagram, TCP message, and app

16、lication message are used where appropriate throughout this tutorial.2.3 Flow of Data Lets follow the data as it flows down through the protocol stack shown in Figure 1. For an application that uses TCP (Transmission Control Protocol), data passes between the application and the TCP module. For appl

17、ications that use UDP (User Datagram Protocol), data passes between the application and the UDP module. FTP (File Transfer Protocol) is a typical application that uses TCP. Its protocol stack in this example is FTP/TCP/IP/ENET. SNMP (Simple Network Management Protocol) is an application that uses UD

18、P. Its protocol stack in this example is SNMP/UDP/IP/ENET. The TCP module, UDP module, and the Ethernet driver are n-to-1 multiplexers. As multiplexers they switch many inputs to one output. They are also 1-to-n de-multiplexers. As de-multiplexers they switch one input to many outputs according to t

19、he type field in the protocol header.Socolofsky & Kale Page 3RFC 1180 A TCP/IP Tutorial January 1991 1 2 3 . n 1 2 3 . n | / | | | / | | / | | | / | - flow - flow |multiplexer| of |de-multiplexer| of - data - data | | | | | v | | 1 1 Figure 2. n-to-1 multiplexer and 1-to-n de-multiplexer If an Ether

20、net frame comes up into the Ethernet driver off the network, the packet can be passed upwards to either the ARP (Address Resolution Protocol) module or to the IP (Internet Protocol) module. The value of the type field in the Ethernet frame determines whether the Ethernet frame is passed to the ARP o

21、r the IP module. If an IP packet comes up into IP, the unit of data is passed upwards to either TCP or UDP, as determined by the value of the protocol field in the IP header. If the UDP datagram comes up into UDP, the application message is passed upwards to the network application based on the valu

22、e of the port field in the UDP header. If the TCP message comes up into TCP, the application message is passed upwards to the network application based on the value of the port field in the TCP header. The downwards multiplexing is simple to perform because from each starting point there is only the

23、 one downward path; each protocol module adds its header information so the packet can be de- multiplexed at the destination computer. Data passing out from the applications through either TCP or UDP converges on the IP module and is sent downwards through the lower network interface driver. Althoug

24、h internet technology supports many different network media, Ethernet is used for all examples in this tutorial because it is the most common physical network used under IP. The computer in Figure 1 has a single Ethernet connection. The 6-byte Ethernet address is unique for each interface on an Ethe

25、rnet and is located at the lower interface of the Ethernet driver. The computer also has a 4-byte IP address. This address is located at the lower interface to the IP module. The IP address must be unique for an internet.Socolofsky & Kale Page 4RFC 1180 A TCP/IP Tutorial January 1991 A running compu

26、ter always knows its own IP address and Ethernet address.2.4 Two Network Interfaces If a computer is connected to 2 separate Ethernets it is as in Figure 3. - | network applications | | | |. | / . | / .| | - - | | |TCP| |UDP| | | - - | | / | | - | | | IP | | | - -*-*- - | | |ARP| | | |ARP| | | - | |

27、 - | | | | / | | - - | | |ENET| |ENET| | | - - | -|-|- | | | -o- | Ethernet Cable 2 -o- Ethernet Cable 1 Figure 3. TCP/IP Network Node on 2 Ethernets Please note that this computer has 2 Ethernet addresses and 2 IP addresses. It is seen from this structure that for computers with more than one physi

28、cal network interface, the IP module is both a n-to-m multiplexer and an m-to-n de-multiplexer.Socolofsky & Kale Page 5RFC 1180 A TCP/IP Tutorial January 1991 1 2 3 . n 1 2 3 . n | | / | | | / | | / | | | / | - flow - flow |multiplexer| of |de-multiplexer| of - data - data / | | | / | | | / | | v / | | | 1 2 3 . m 1 2 3 . m Figure 4. n-to-m multiplexer and m-to-n de-multiplexer It performs th