CommTech Training Center
Network Fundamental
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Preface
•Known as TCP/IP
•TCP/IP is Everywhere
•Millions of people use TCP/IP and the Internet without really knowing how they work
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Scope
•Theory versus Practice
•Current versus Future Protocols
•Application Coverage
•TCP/IP versus The Internet
•Limited TCP/IP Security Coverage
•Small Computer Orientation
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Network Fundamental : What is Network ?
•A collection of computers or other hardware devices that are connected together, either physically or logically, using special hardware and software, to allow them to exchange information and cooperate.
•Networking is the term that describes the processes involved in designing, implementing, upgrading, managing and otherwise working with networks and network technologies.
The Advantages (Benefits) of Networking
•Connectivity and Communication
•Data Sharing
•Hardware Sharing
•Internet Access
•Internet Access Sharing
•Data Security and Management
•Performance Enhancement and Balancing
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The Disadvantages (Costs) of Networking
•Network Hardware, Software and Setup Costs
•Hardware and Software Management and Administration Costs
•Undesirable Sharing
•Illegal or Undesirable Behavior
•Data Security Concerns
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Networking Layers, Models and Architectures
•People find networking difficult to learn is that it can be a very complicated subject.
•Networks consist of so many hardware and software elements.
•In order for even the simplest task to be accomplished on a network, dozens of different components must cooperate, passing control information and data to accomplish the overall goal of network communication.
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Protocols: What Are They, Anyway?
• A protocol often refers to a code of conduct, or a form of etiquette observed by diplomats.
•These people must follow certain rules of ceremony and form to ensure that they communicate effectively, and without coming into conflict.
•They also must understand what is expected of them when they interact with representatives from other nations, to make sure that, for example, they do not offend due to unfamiliarity with local customs.
•Even e o al people follo p oto ols of a ious so ts, hi h a e so t of
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Protocols: Description
•Protocol is basically a way of ensuring that devices are able to talk to each other effectively
•Ex : How protocol works on OSI Model Reference
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Circuit Switching and Packet Switching Networks
•Circuit Switching
•In this networking method, a connection called acircuitis set up between two devices,
which is used for the whole communication. Information about the nature of the circuit is maintained by the network.
Comparing Circuit Switching and Packet Switching
• A common te ptatio he o side i g alte ati es su h as these is to ask hi h is ette —and as usually
is the ase, the a s e is eithe . The e a e pla es he e o e is o e suited tha the othe , ut if o e e e
clearly superior, both methods wouldn't be used.
•One important issue in selecting a switching method is whether the network medium issharedordedicated,
Your phone line can be used for establishing a circuit because you are the only one who can use it. •The ability to have many devices communicate simultaneously without dedicated data paths is one reason why
packet switching is becoming predominant today
•While the theoretical difference between circuit and packet switching is pretty clear-cut, understanding how they are used is a bit more complicated. One of the major issues is that in modern networks, they are often combined. For example, suppose you connect to the Internet using a dial-up modem. You will be using IP datagrams (packets) to carry higher-layer data, but it will be over the circuit-switched telephone network. Yet the data may be sent over the telephone system in digital packetized form. So in some ways, both circuit switching and packet switching are being used concurrently.
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Packet Switching
•In this network type, no specific path is used for data transfer. Instead, the data is chopped up into small pieces called packets and sent over the network. The packets can be routed, combined or fragmented, as required to get them to their eventual destination. On the receiving end, the process is reversed—the data is read from the packets and re-assembled into the form of the original data.
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Connection-Oriented and Connectionless
Protocols
•Protocols are divided into two categories based on their use of connections:
•Connection-Oriented Protocols: These protocols require that a logical connection be
established between two devices before transferring data. This is generally accomplished by following a specific set of rules that specify how a connection should be initiated, negotiated, managed and eventually terminated. Usually one device begins by sending a request to open a connection, and the other responds. They pass control information to determine if and how the connection should be set up. If this is successful, data is sent between the devices. When they are finished, the connection is broken.
•Connectionless Protocols: These protocols do not establish a connection between
devices. As soon as a device has data to send to another, it just sends it.
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Common Names For Messages
•Packet: This term is considered by many to most correctly refer to a message sent by protocols operating at the network
laye of the O“I Refe e e Model. “o, you ill o o ly see people efe to IP pa kets . Ho e e , this te is o o ly
also used to refer generically to any type of message, as I mentioned at the start of this topic.
•Datagram: This te is asi ally sy o y ous ith pa ket a d is also used to efe to et o k laye te h ologies. It is also ofte used to efe to a essage that is se t at a highe le el of the O“I Refe e e Model o e ofte tha pa ket is .
•Frame: This term is most commonly associated with messages that travel at low levels of the OSI Reference Model. In particular, it is most commonly seen used in reference to data link layer messages. It is occasionally also used to refer to physical layer messages, when message formatting is performed by a layer one technology. A frame gets its name from the fact that it is created by taking higher-le el pa kets o datag a s a d f a i g the ith additio al heade i fo atio
needed at the lower level.
•Cell: Frames and packets, in general, can be of variable length, depending on their contents; in contrast, a cell is most often a message that is fixed in size. For example, the fixed-length, 53-byte messages sent in Asynchronous Transfer Mode (ATM) are called cells. Like frames, cells usually are used by technologies operating at the lower layers of the OSI model. •Protocol Data Unit (PDU) and Service Data Unit (SDU): These are the formal terms used in the OSI Reference to describe
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Message Formatting: Headers, Payloads and
Footers
•Messagesare the structures used to send information over networks.
• Header: Information that is placed before the actual data. The header normally contains a small number of bytes of control information, which is used to communicate important facts about the data that the message contains and how it is to be interpreted and used. It serves as the communication and control link between protocol elements on different devices.
• Data: The actual data to be transmitted, often called the payload of the message (metaphorically borrowing a term from the space industry!) Most messages contain some data of one form or another, but some actually contain none: they are used only for control and communication purposes. For example, these may be used to set up or terminate a logical connection before data is sent.
• Footer: Information that is placed after the data. There is no real difference between the header and the footer, as both generally contain control fields. The term trailer is also sometimes used.
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Message Addressing and Transmission Methods:
Unicast, Broadcast and Multicast Messages
Network Structural Models and Client/Server and
Peer-to-Peer Networking
•that networks are normally set up for two primary purposes: connectivity and sharing
•One very important issue in network design is how to configure the network for the sharing of resources. Specifically, the network designer must decide whether or not to dedicate resource management functions to the devices that constitute it. In some networks, all devices are treated equal in this regard, while in others, each computer is responsible for a particular job in the overall function of providing services. In this latter arrangement, the devices are sometimes said to haveroles, somewhat like actors in a play.
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Types and Sizes of Networks :
Local Area Networks (LANs), Wireless LANs (WLANs) and Wide Area Networks (WANs) and Variants (CANs, MANs and PANs)
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Network Performance and QOS (next chapter)
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Network Standards and Standards Organizations
•International Organization for Standardization (ISO)
•American National Standards Institute (ANSI)
•Information Technology Industry Council (ITIC)
•National Committee for Information Technology (NCITS)
•Institute of Electrical and Electronics Engineers (IEEE)
•Electronic Industries Alliance (EIA)
•Telecommunications Industry Association (TIA)
•International Telecommunication Union - Telecommunication Standardization Sector (ITU-T)
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Internet Standards Organizations (ISOC, IAB, IESG,
IETF, IRSG, IRTF)
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Internet Registration Authorities and Registries
(IANA, ICANN, APNIC, ARIN, LACNIC, RIPE NCC)
•Parameter Standardization:Most protocols rely on the use of parameters that control how
they function. As just two of many, many examples, the Internet Protocol has a set of numbers that define different IP options, and the Address Resolution Protocol (ARP) has anOperation Codefield that can take on many different values. Just as it is essential for devices to agree on what protocols to use, they must also agree on what parameters to use for those protocols, if communication is to be successful.
•Global Resource Allocation and Identifier Uniqueness:There are a number of resources
that are used on the Internet that must be allocated from a fixed set of values and where uniqueness in assignment is essential. The most obvious example is that each TCP/IP host must have a unique IP address; another important example is ensuring that only one organization uses a given DNS domain name. If two devices have the same IP address or two organizations try to use the same domain name, the results would be unpredictable, but almost certainly bad.
Internet Registration Authorities and Registries
(IANA, ICANN, APNIC, ARIN, LACNIC, RIPE NCC)
•In the original classful IP add essi g s he e, add esses e e assig ed toorganizations directly by IANA in address blocks: Class A, Class B and Class C addresses
•Asia Pacific Network Information Centre (APNIC):Covers the Asia/Pacific region.
•American Registry for Internet Numbers (ARIN):Manages North America, part of the Caribbean, and sub-equatorial Africa.
•Latin American and Caribbean Internet Addresses Registry (LACNIC):Responsible for Latin America and part of the Caribbean.
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The Open System Interconnection (OSI) Reference
Model
•Models are useful because they help us understand difficult concepts and complicated systems. When it comes to networking, there are several models that are used to explain the roles played by various technologies, and how they interact.
•The idea behind the OSI Reference Model is to provide a framework for both designing networking systems and for explaining how they work
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The Benefits of Networking Models
•Training and Documentation:It is easier to explain how to build a complex system by
breaking the process into smaller parts. Training can be done for a specific job without everyone needing to know how everything else works.
•Specialization:If everyone is responsible for doing every job, nobody gets enough
experience to become an expert at anything. Through specialization, certain individuals develop expertise at particular jobs.
•Easier Design Modification and Enhancement:Separating the automobile into systems, and
particular jobs required to build those systems, makes it easier to make changes in the future. Without such divisions, it would be much more difficult to determine what the impact might be of a change, which would serve as a disincentive for innovation.
•Modularity:This is related to each of the items above. If the automobile's systems and
manufacturing steps are broken down according to a sensible architecture or model, it becomes easier to interchange parts and procedures between vehicles. This saves time and money.
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OSI Reference Model Data Encapsulation
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Message Routing in the OSI Reference Model
Phase OSI Layer CEO Letter Web Site Connection (Simplified)
Transmission
7 The CEO of a company in Phoenix decides he needs to send a letter to a peer of his in Albany. He dictates the letter to his administrative assistant.
You decide you want to connect to the web server at IP address 10.0.12.34, which is within your organization but not on your local network. You type the address into your browser.
6 The administrative assistant transcribes the dictation into writing. (Generally, with a web site connection, nothing happens at this layer, but format translation may be done in some cases.)
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The administrative assistant puts the letter in an envelope and gives it to the mail room. The assistant doesn't actually know how the letter will be sent, but he knows it is urgent so he says,getthis to its destinationui kly.
The request is sent via a call to an application program interface (API), to issue the command necessary to contact the server at that address.
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The mail room must decide how to get the letter where it needs to go. Since it is a rush, the people in the mail room decide they must use a courier. The envelope is given to the courier company to send.
The Transmission Control Protocol (TCP) is used to create a segment to be sent to IP address 10.0.12.34.
Routing 3
The courier company receives the envelope, but it needs to add its own handling information, so it places the smaller envelope in a courier envelope (encapsulation). The courier then consults its airplane route information and determines that to get this envelope to Albany, it must be flown through its hub in Chicago. It hands this envelope to the workers who load packages on airplanes.
Your computer creates an IP datagram encapsulating the TCP datagram created above. It then addresses the packet to 10.0.12.34. but discovers that it is not on its local network. So instead, it realizes it needs to send the message to its designated routing device at IP address 10.0.43.21. It hands the packet to the driver for your Ethernet card (the software that interfaces to the Ethernet hardware).
2 The workers take the courier envelope and put on it a tag with the code for Chicago. They then put it in a handling box and then load it on the plane to Chicago.
The Ethernet card driver forms a frame containing the IP datagram and prepares it to be sent over the network. It packages the message and puts the address 10.0.43.21 (for the router) in the frame.
1 The plane flies to Chicago.
The frame is sent over the twisted pair cable that connects your local area network. (I'm ignoring overhead, collisions, etc. here, but then I also ignored the possibility of collisions with the plane. J)
2 In Chicago, the box is unloaded, and the courier envelope is removed from it and given to the people who handle routing in Chicago.
The Ethernet card at the machine with IP address 10.0.43.21 receives the frame, strips off the frame headers and hands it up to the network layer.
3 The tag markedChi agois removed from the outside of the courier envelope. The envelope is then given back to the airplane workers to be sent to Albany.
The IP datagram is processed by the router, which realizes the destination (10.0.12.34) can be reached directly. It passes the datagram back down to the Ethernet driver. 2 The envelope is given a new tag with the code for Albany, placed in another box and
loaded on the plane to Albany.
The Ethernet driver creates a new frame and prepares to send it to the device that uses IP address 10.0.12.34.
1 The plane flies to Albany. The frame is sent over the network.
2 The box is unloaded and the courier envelope is removed from the box. It is given to the Albany routing office.
The Ethernet card at the device with IP address 10.0.12.34 receives the frame, strips off the headers and passes it up the stack.
Reception
3 The courier company in Albany sees that the destination is in Albany, and delivers the
envelope to the destination CEO's company. The IP headers are removed from the datagram and the TCP segment handed up to TCP.
4 The mail room removes the inner envelope from the courier envelope and delivers it to
the destination CEO's assistant. TCP removes its headers and hands the data up to the drivers on the destination machine. 5 The assistant takes the letter out of the envelope. The request is sent to the Web server software for processing.
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Physical Layer (Layer 1)
•The following are the main responsibilities of the physical layer in the OSI Reference Model:
•Definition of Hardware Specifications: The details of operation of cables, connectors,
wireless radio transceivers, network interface cards and other hardware devices are generally a function of the physical layer (although also partially the data link layer; see below).
•Encoding and Signaling: The physical layer is responsible for various encoding and signaling
functions that transform the data from bits that reside within a computer or other device into signals that can be sent over the network.
•Data Transmission and Reception: After encoding the data appropriately, the physical layer
actually transmits the data, and of course, receives it. Note that this applies equally to wired and wireless networks, even if there is no tangible cable in a wireless network!
•Topology and Physical Network Design: The physical layer is also considered the domain of
many hardware-related network design issues, such as LAN and WAN topology.
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Data Link Layer Functions
•The following are the key tasks performed at the data link layer:
•Logical Link Control (LLC): Logical link control refers to the functions required for the establishment and control of logical links between local devices on a network. As mentioned above, this is usually considered a DLL sublayer; it provides services to the network layer above it and hides the rest of the details of the data link layer to allow different technologies to work seamlessly with the higher layers. Most local area networking technologies use the IEEE 802.2 LLC protocol.
•Media Access Control (MAC): This refers to the procedures used by devices to control access to the network medium. Since many networks use a shared medium (such as a single network cable, or a series of cables that are electrically connected into a single virtual medium) it is necessary to have rules for managing the medium to avoid conflicts. For example. Ethernet uses the CSMA/CD method of media access control, while Token Ring uses token passing.
•Data Framing: The data link layer is responsible for the final encapsulation of higher-level messages into frames that are sent over the network at the physical layer.
•Addressing: The data link layer is the lowest layer in the OSI model that is concerned with addressing: labeling information with a particular destination location. Each device on a network has a unique number, usually called a hardware address or MAC address, that is used by the data link layer protocol to ensure that data intended for a specific machine gets to it properly.
•Error Detection and Handling: The data link layer handles errors that occur at the lower levels of the network stack. For example, a cyclic redundancy check (CRC) field is often employed to allow the station receiving data to detect if it was received correctly.
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Network Layer Functions
•Some of the specific jobs normally performed by the network layer include:
•Logical Addressing: Every device that communicates over a network has associated with it a logical address, sometimes called a layer three address. For example, on the Internet, the Internet Protocol (IP) is the network layer protocol and every machine has an IP address. Note that addressing is done at the data link layer as well, but those addresses refer to local physical devices. In contrast, logical addresses are independent of particular hardware and must be unique across an entire internetwork.
•Routing: Moving data across a series of interconnected networks is probably the defining function of the network layer. It is the job of the devices and software routines that function at the network layer to handle incoming packets from various sources, determine their final destination, and then figure out where they need to be sent to get them where they are supposed to go. I discuss routing in the OSI model more completely in this topic on the topic on indirect device connection, and show how it works by way of an OSI model analogy.
•Datagram Encapsulation: The network layer normally encapsulates messages received from higher layers by placing them into datagrams (also called packets) with a network layer header.
•Fragmentation and Reassembly: The network layer must send messages down to the data link layer for transmission. Some data link layer technologies have limits on the length of any message that can be sent. If the packet that the network layer wants to send is too large, the network layer must split the packet up, send each piece to the data link layer, and then have pieces reassembled once they arrive at the network layer on the destination machine. A good example is how this is done by the Internet Protocol.
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Network Layer Functions
•Network Layer Connection-Oriented and Connectionless Services
•Network layer protocols may offer either connection-oriented or connectionless services for delivering packets across the network. Connectionless ones are by far more common at the network layer. In many protocol suites, the network layer protocol is connectionless, and connection-oriented services are provided by the transport layer. For example, in TCP/IP, the Internet Protocol (IP) is connectionless, while the layer four Transmission Control Protocol (TCP) is connection-oriented.
•The most common network layer protocol is of course the Internet Protocol (IP), which is why I have already mentioned it a couple of times. IP is the backbone of the Internet, and the foundation of the entire TCP/IP protocol suite. There are also several protocols directly related to IP that work with it at the network layer, such as IPsec, IP NAT and Mobile IP. ICMP is the main error-handling and control protocol that is used along with IP. Another notable network layer protocol outside the TCP/IP world is the Novell IPX protocol.
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Transport layer
•Transport Layer Services and Transmission Quality Accomplishing this communication between processes requires that the transport layer perform several different, but related jobs. For transmission, the transport layer protocol must keep track of what data comes from each application, then combine this data into a single flow of data to send to the lower layers. The device receiving information must reverse these operations, splitting data and funneling it to the appropriate recipient processes. The transport layer is also responsible for defining the means by which potentially large amounts of application data are divided into smaller blocks for transmission.
•Another key function of the transport layer is to provideconnection servicesfor the
protocols and applications that run at the levels above it. These can be categorized as either connection-oriented services or connectionless services. Neither is better or worse than the other; they each have their uses. While connection-oriented services can be handled at the network layer as well, they are more often seen in the transport layer in the
eal o ld . “o e p oto ol suites, su h as TCP/IP, p o ide oth a o e tio-oriented and a
connectionless transport layer protocol, to suit the needs of different applications.
Transport Layer Functions
•Process-Level Addressing:Addressing at layer two deals with hardware devices on a local network, and layer three addressing identifies devices on a logical internetwork. Addressing is also performed at the transport layer, where it is used to differentiate between software programs. This is part of what enables many different software programs to use a network layer protocol simultaneously, as mentioned above. The best example of transport-layer process-level addressing is the TCP and UDP port mechanism used in TCP/IP, which allows applications to be individually referenced on any TCP/IP device.
•Multiplexing and Demultiplexing:Using the addresses I just mentioned, transport layer protocols on a sending devicemultiplexthe data received from many application programs for transport, combining them into a single stream of data to be sent. The same protocols receive data and thendemultiplexit from the incoming stream of datagrams, and direct each package of data to the appropriate recipient application processes.
•Segmentation, Packaging and Reassembly:The transport layer segments the large amounts of data it sends over the network into smaller pieces on the source machine, and then reassemble them on the destination machine. This function is similar conceptually to the fragmentation function of the network layer; just as the network layer fragments messages to fit the limits of the data link layer, the transport layer segments messages to suit the requirements of the underlying network layer.
•Connection Establishment, Management and Termination:Transport layer connection-oriented protocols are responsible for the series of communications required to establish a connection, maintain it as data is sent over it, and then terminate the connection when it is no longer required.
•Acknowledgments and Retransmissions:As mentioned above, the transport layer is where many protocols are implemented that guarantee reliable delivery of data. This is done using a variety of techniques, most commonly the combination ofacknowledgmentsandretransmission timers. Each time data is sent a timer is started; if it is received, the recipient sends back an acknowledgment to the transmitter to indicate successful transmission. If no acknowledgment comes back before the timer expires, the data is retransmitted. Other algorithms and techniques are usually required to support this basic process.
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Session layer
•The fifth layer in the OSI Reference Model layer is the session layer. As its name suggests, it is the layer intended to provide functions for establishing and managing sessions between software processes. Session layer technologies are often implemented as sets of software tools called application program interfaces (APIs), which provide a consistent set of services that allow programmers to develop networking applications without needing to worry about lower-level details of transport, addressing and delivery.
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Presentation Layer Functions
•Translation:Networks can connect very different types of computers together: PCs,
Macintoshes, UNIX systems, AS/400 servers and mainframes can all exist on the same network. These systems have many distinct characteristics and represent data in different ways; they may use different character sets for example. The presentation layer handles the job of hiding these differences between machines.
•Compression:Compression (and decompression) may be done at the presentation layer to
improve the throughput of data. (There are some who believe this is not, strictly speaking, a function of the presentation layer.)
•Encryption:Some types of encryption (and decryption) are performed at the presentation
layer. This ensures the security of the data as it travels down the protocol stack. For example, one of the most popular encryption schemes that is usually associated with the presentation layer is the Secure Sockets Layer (SSL) protocol. Not all encryption is done at layer 6, however; some encryption is often done at lower layers in the protocol stack, in technologies such as IPSec.
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Application layer
Group # Layer Name Key Responsibilities Data Type Handled Scope Common Protocols and Technologies
Lower Layers
1 Physical Encoding and Signaling; Physical Data Transmission; Hardware Specifications; Topology and Design Bits
Electrical or light signals sent between
local devices
(Physical layers of most of the technologies listed for the data
link layer)
2 Data Link
Logical Link Control; Media Access Control; Data Framing; Addressing; Error Detection and Handling;
Defining Requirements of Physical Layer Frames
Low-level data messages between
local devices
IEEE 802.2 LLC, Ethernet Family; Token Ring; FDDI and CDDI; IEEE 802.11 (WLAN, Wi-Fi); HomePNA; HomeRF; ATM; SLIP
and PPP
3 Network Encapsulation; Fragmentation and Reassembly; Error Logical Addressing; Routing; Datagram Handling and Diagnostics
Datagrams / Packets Messages between local or remote devices
IP; IPv6; IP NAT; IPsec; Mobile IP; ICMP; IPX; DLC; PLP; Routing
protocols such as RIP and BGP
4 Transport
5 Session Session Establishment, Management and Termination Sessions Sessions between local or remote devices
NetBIOS, Sockets, Named Pipes, RPC
6 Presentation Data Translation; Compression and Encryption Encoded User Data Application data
representations SSL; Shells and Redirectors; MIME
7 Application User Application Services User Data Application data
DNS; NFS; BOOTP; DHCP;
•TheInternet Protocol (IP)is the primary OSI network layer (layer three)
protocol that provides addressing, datagram routing and other functions in an internetwork. TheTransmission Control Protocol (TCP)is the primary transport layer (layer four) protocol, and is responsible for connection establishment and management and reliable data transport between software processes on devices.
TCP/IP Protocols
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Important Factors in the Success of TCP/IP
•Integrated Addressing System:TCP/IP includes within it (as part of the Internet Protocol, primarily) a system for identifying and addressing devices on both small and large networks. The addressing system is designed to allow devices to be addressed regardless of the lower-level details of how each constituent network is constructed. Over time, the mechanisms for addressing in TCP/IP have improved, to meet the needs of growing networks, especially the Internet. The addressing system also includes a centralized administration capability for the Internet, to ensure that each device has a unique address.
•Design For Routing:Unlike some network-layer protocols, TCP/IP is specifically designed to facilitate the routing of information over a network of arbitrary complexity. In fact, TCP/IP is conceptually concerned more with the connection of networks, than with the connection of devices. TCP/IP routers enable data to be delivered between devices on different networks by moving it one step at a time from one network to the next. A number of support protocols are also included in TCP/IP to allow routers to exchange critical information and manage the efficient flow of information from one network to another.
•Underlying Network Independence:TCP/IP operates primarily at layers three and above, and includes provisions to allow it to function on almost any lower-layer technology, including LANs, wireless LANs and WANs of various sorts. This flexibility means that one can mix and match a variety of different underlying networks and connect them all using TCP/IP.
•Scalability:One of the most amazing characteristics of TCP/IP is how scalable its protocols have proven to be. Over the decades it has proven its mettle as the Internet has grown from a small network with just a few machines to a huge internetwork with millions of hosts. While some changes have been required periodically to support this growth, these changes have taken place as part of the TCP/IP development process, and the core of TCP/IP is basically the same as it was 25 years ago.
•Open Standards and Development Process:The TCP/IP standards are not proprietary, but open standards freely available to the public. Furthermore, the process used to develop TCP/IP standards is also completely open. TCP/IP standards and protocols are developed and modified using the unique, de o ati RFC p o ess, ith all i te ested pa ties i ited to pa ti ipate. This e su es that a yo e ith a i te est i the TCP/IP protocols is given a chance to provide input into their development, and also ensures the world-wide acceptance of the protocol suite.
•Universality:Everyone uses TCP/IP because everyone uses it!
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Understanding TCP/IP Client and Server Roles
•The te s lie t a d se e a e o fusi g i TCP/IP e ause they a e used i se e al diffe e t
ways, sometimes simultaneously:
•Hardware Roles:The te s lie t a d se e usually efe to the p i a y oles played y
et o ked ha d a e. A lie t o pute is usually so ethi g like a PC o Ma i tosh o pute used y a i di idual, a d p i a ily i itiates o e satio s y se di g e uests. A se e is usually
a very high-powered machine dedicated to responding to client requests, sitting in a computer room somewhere that nobody but its administrator ever sees.
•Software Roles:As mentioned earlier, TCP/IP uses different pieces of software for many protocols to
i ple e t lie t a d se e oles. A We o se is a pie e of lie t soft a e, hile We se e
software is completely different. Client software is usually found on client hardware and server software on server hardware, butnot always. Some devices may run both client and server software.
•Transactional Roles:In any exchange of information, the client is normally the device that initiates communication or sends a query; the server responds, usually providing information. Again, usually the client software on a client device initiates the transaction, but this is not always the case.
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TCP/IP Protocols: Network Interface Layer (OSI
Layer 2)
Protocol Name Protocol Abbr. Description
Serial Line Internet Protocol
(SLIP) SLIP
Provides basic TCP/IP functionality by creating a layer-two connection between layer-two devices over a serial line.
Point-to-Point Protocol PPP
Provides layer-two connectivity like SLIP, but is much more sophisticated and capable. PPP
is itself a suite of protocols (“sub
-protocols” if you will) that allow
for functions such as authentication, data encapsulation, encryption and aggregation, facilitating TCP/IP operation over WAN links.
Protocols: Network Interface / Network Layer
O“I Layer /
Protocol Name Protocol Abbr. Description
Address Resolution Protocol ARP
Used to map layer three IP addresses to layer two physical network addresses.
Reverse Address Resolution
Protocol RARP
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TCP/IP Protocols: Network Layer (OSI Layer 3)
Protocol Name Protocol Abbr. Description
Internet Protocol, Internet Protocol Version 6 IP, IPv6
Provides encapsulation and connectionless delivery of transport layer messages over a TCP/IP network. Also responsible for addressing and routing functions.
IP Network Address Translation IP NAT
Allows addresses on a private network to be automatically translated to different addresses on a public network, providing address sharing and
security benefits. (Note that some people don’t
consider IP NAT to be a protocol in the strict sense of that word.)
IP Security IPSec A set of IP-related protocols that improve the security of IP transmissions.
Internet Protocol Mobility Support Mobile IP Resolves certain problems with IP associated with mobile devices.
Internet Control Message Protocol ICMP/ICMPv4, ICMPv6 A “support protocol” for IP and IPv6 that provides error-reporting and information request-and-reply capabilities to hosts.
Neighbor Discovery Protocol ND A new “support protocol” for IPv6 that includes several functions performed by ARP and ICMP in conventional IP.
Routing Information Protocol, Open Shortest Path First, Gateway-to-Gateway Protocol, HELLO Protocol, Interior Gateway Routing Protocol, Enhanced Interior Gateway Routing Protocol, Border Gateway Protocol, Exterior Gateway Protocol
RIP, OSPF, GGP, HELLO, IGRP, EIGRP, BGP, EGPProtocols used to support the routing of IP datagrams and the exchange of routing information.
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TCP/IP Protocols: Host-to-Host Transport Layer
(OSI Layer 4)
Protocol Name Protocol Abbr. Description
Transmission Control
Protocol TCP
The main transport layer protocol for TCP/IP. Establishes and manages connections between devices and ensures reliable and flow-controlled delivery of data using IP.
User Datagram Protocol UDP
A transport protocol that can be considered a “severely
stripped-down” version of TCP. It is used to send data in a
simple way between application processes, without the many reliability and flow management features of TCP, but often with greater efficiency.
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TCP/IP Protocols: Application Layer (OSI Layer
5/6/7)
Protocol Name Protocol Abbr. Description
Domain Name System DNS Provides the ability to refer to IP devices using names instead of just numerical IP addresses. Allows machines to resolve these names into their corresponding IP addresses.
Network File System NFS Allows files to be shared seamlessly across TCP/IP networks.
Bootstrap Protocol BOOTP Developed to address some of the issues with RARP and used in a similar manner: to allow the configuration of a TCP/IP device at startup. Generally superseded by DHCP.
Dynamic Host
Configuration Protocol DHCP A complete protocol for configuring TCP/IP devices and managing IP addresses. The successor to RARP and BOOTP, it includes numerous features and capabilities.
Simple Network Management Protocol SNMP A full-featured protocol for remote management of networks and devices.
Remote Monitoring RMON A diagnostic “protocol” (really a part of SNMP) used for remote monitoring of network devices.
File Transfer Protocol, Trivial File
Transfer Protocol FTP, TFTP Protocols designed to permit the transfer of all types of files from one device to another.
RFC 822, Multipurpose Internet Mail Extensions, Simple Mail Transfer Protocol, Post Office Protocol, Internet
Message Access Protocol
RFC 822, MIME, SMTP,
POP, IMAP Protocols that define the formatting, delivery and storage of electronic mail messages on TCP/IP networks.
Network News Transfer Protocol NNTP Enables the operation of the Usenet online community by transferring Usenet news messages between hosts.
Hypertext Transfer Protocol HTTP Transfers hypertext documents between hosts; implements the World Wide Web.
Gopher Protocol Gopher An older document retrieval protocol, now largely replaced by the World Wide Web.
Telnet Protocol Telnet Allows a user on one machine to establish a remote terminal session on another.
Berkeley “r” Commands — Permit commands and operations on one machine to be performed on another.
Internet Relay Chat IRC Allows real-time chat between TCP/IP users.
Administration and Troubleshooting
