Guide to TCP/IP, Second Edition1 Guide To TCP/IP, Second Edition Chapter 6 Basic TCP/IP Services

Guide to TCP/IP, Second Edition2 Objectives Understand how TCP/IP Application layer protocols and services work Explain the capabilities, message types, and request/reply architectures for a variety of basic TCP/IP services, including FTP, Telnet, SMTP, and HTTP Understand the operations of other basic TCP/IP services, including Echo, Whois, TFTP, Finger, Remote Procedure Call (RPC), NetBIOS services over TCP/IP (also known as NBT), and SNMP

Guide to TCP/IP, Second Edition3 Objectives (cont.) Explain how to decode packets that contain Application layer protocols, and how to relate message types or other similar information to the kinds of requests and replies moving between a client and a server (or between hosts in general)

Guide to TCP/IP, Second Edition4 How Application Layer IP Protocols Work And Behave Conventions and behaviors –Specifications for the message structures that the protocol or service supports –Definition of a well-known port address (or addresses) on which servers listen for service requests –Availability of appropriate software components that implement the various roles that hosts can play in requesting or providing such services

Guide to TCP/IP, Second Edition5 How Application Layer IP Protocols Work And Behave (cont.) Request/reply messages Client/server architecture Peer-to-peer services Server-to-server traffic –Load balancing –Replication –Pull –Push –Push-pull

Guide to TCP/IP, Second Edition6 Understanding FTP FTP User Interface (UI) Protocol Interpreter (PI) FTP Commands Data Transfer Process (DTP) File System

Guide to TCP/IP, Second Edition7 Understanding FTP (cont.) TCP Transport TCP-based Command Connection TCP-based Data Transfer Connection

Guide to TCP/IP, Second Edition8 Understanding FTP (cont.)

Guide to TCP/IP, Second Edition9 Understanding FTP (cont.)

Guide to TCP/IP, Second Edition10 Understanding FTP (cont.)

Guide to TCP/IP, Second Edition11 Understanding FTP (cont.)

Guide to TCP/IP, Second Edition12 Sample FTP Communications

Guide to TCP/IP, Second Edition13 Sample FTP Communications (cont.)

Guide to TCP/IP, Second Edition14 Sample FTP Communications (cont.)

Guide to TCP/IP, Second Edition15 Sample FTP Communications (cont.)

Guide to TCP/IP, Second Edition16 Understanding Telnet Bidirectional byte-oriented communication Terminal Access Well-known Port 23 server side Dynamic port number client side

Guide to TCP/IP, Second Edition17 Sample Telnet Communications

Guide to TCP/IP, Second Edition18 Packet-By-Packet Sequence

Guide to TCP/IP, Second Edition19 Packet-By-Packet Sequence (cont.)

Guide to TCP/IP, Second Edition20 Understanding SMTP SMTP elements –Sender-SMTP and Receiver-SMTP –SMTP commands and extensions –SMTP reply codes

Guide to TCP/IP, Second Edition21 Understanding SMTP (cont.)

Guide to TCP/IP, Second Edition22 Sample SMTP Communications

Guide to TCP/IP, Second Edition23 Sample SMTP Communications (cont.)

Guide to TCP/IP, Second Edition24 Understanding HTTP Http elements –URIs Uniform Resource Locator (URL) Uniform Resource Name (URN) –HTTP methods –Status codes

Guide to TCP/IP, Second Edition25 Understanding HTTP (cont.)

Guide to TCP/IP, Second Edition26 Understanding HTTP (cont.)

Guide to TCP/IP, Second Edition27 Sample HTTP Communications

Guide to TCP/IP, Second Edition28 Packet-By-Packet Sequence

Guide to TCP/IP, Second Edition29 Packet-By-Packet Sequence (cont.)

Guide to TCP/IP, Second Edition30 Other Common IP-based Services Echo (TCP and UDP) Whois Trivial File Transfer Protocol (TFTP)

Guide to TCP/IP, Second Edition31 Decoding Application Layer Protocols Decoding TCP/IP Application layer traffic largely depends on two separate but simultaneous forms of analysis –Understanding request/reply messages, recognize related headers and payload information –Assemble multiple lower-layer packets to reconstitute Application layer messages

Guide to TCP/IP, Second Edition32 Decoding Application Layer Protocols (cont.)

Guide to TCP/IP, Second Edition33 Decoding Application Layer Protocols (cont.)

Guide to TCP/IP, Second Edition34 Other Common IP-based Services (cont.) Finger Remote Procedure Call (RPC) Simple Network Management Protocol (SNMP) NetBIOS over TCP/IP

Guide to TCP/IP, Second Edition35 Chapter Summary The foundation upon which all TCP/IP Application layer services rest is a request/reply message architecture, in which clients send requests and servers issue corresponding replies When the client and server roles are clearly distinct and separate, such services may be called client/server services; when a client can also act as a server and vice versa, such services may be called peer-to-peer services

Guide to TCP/IP, Second Edition36 Chapter Summary (cont.) Among its hundreds of Application layer services, the TCP/IP protocol suite includes many instances of both kinds Certain client/server Application layer services also involve server-to-server traffic, in which multiple servers cooperate to share common data The sharing process is called replication and may occur as a push operation, in which the sending server initiates data transfer, or as a pull operation, in which the receiving server initiates data transfer

Guide to TCP/IP, Second Edition37 Chapter Summary (cont.) Some TCP/IP Application layer services even use push- pull replication, so that a server whose data was changed can immediately push its data to replication partners after the change is completed, but other servers can also request replication at regular intervals to make sure their copies of data are as current as possible FTP is a file transfer service that permits a local host to connect to a remote host, navigate and manage files on the remote system, and transfer files to and from that remote host Although FTP is an old TCP/IP service, it remains useful today

Guide to TCP/IP, Second Edition38 Chapter Summary (cont.) Telnet provides a method to log on and access the command line on a remote computer using TCP/IP, a technique known as terminal emulation (because it makes the local host behave as if it were a terminal attached to the remote host) Because Telnet provides a convenient way to operate on a remote host across a network, it too remains useful to this day Security problems with Telnet (especially moving account and password information as clear text) prompted development and widespread adoption of Secure Telnet implementations in many organizations

Guide to TCP/IP, Second Edition39 Chapter Summary (cont.) SMTP provides store and forward services for e- mail messages, and manages how is routed from its sender to its designated receiver(s) SMTP makes global possible on today’s Internet, and continues to deliver one of the most useful and valuable networking services around

Guide to TCP/IP, Second Edition40 Chapter Summary (cont.) HTTP provides the underpinnings for the leading service and protocol used on today’s Internet—namely the World Wide Web HTTP’s rich collection of message types, and its ability to invoke other protocols (including , news, and FTP), make it a powerful tool for general remote data access Its hyperlinking abilities make it easy for users to move rapidly through huge information spaces and explain why the Web is so compelling and appealing to most Internet users

Guide to TCP/IP, Second Edition41 Chapter Summary (cont.) Other common TCP/IP Application layer services include Echo (which echoes the data delivered to a receiver back to the sender), TFTP, Finger, Remote Procedure Call (RPC), NetBIOS over TCP/IP (also known as NBT), and SNMP

Guide to TCP/IP, Second Edition42 Chapter Summary (cont.) Understanding how to decode Application layer protocols means learning how to identify and interpret request and reply messages related to such protocols, and how to reassemble related payloads, when necessary Fortunately, many modern protocol analyzers (for example, Ethereal) are able to assist with this task