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    "antivirus" is protective software designed to defend your computer against

    malicious software. Malicious software, or "malware" includes: viruses, Trojans,

    keyloggers, hijackers, dialers, and other code that vandalizes or steals your

    computer contents. In order to be an effective defense, your antivirus software

    needs to run in the background at all times, and should be kept updated so it

    recognizes new versions of malicious software.

    Significance Every computer connected to the Internet or on a network needs to have an antivirus program

    installed. Virus prevention is an essential component needed by everyon

    Viruses A virus is a software program that infects computers without the owners' permission. Virusesare different from other forms of malware in that viruses are spread from one computer to the

    next.

    Antivirus

    Antivirus software scans for infections on a computer. Some antivirus programs includeautomated scheduled scannings and additional features.

    Types of AntivirusCommercial antivirus and Internet security programs are available, such as Norton andMcAfee. Free programs include AVG Free and Avira.

    What are Routing Protocols?

    A routing protocol is the implementation of arouting algorithm in software or hardware.

    A routing protocol uses metrics to determine which path to utilize to transmit a packet across aninternetwork.

    The metrics used by routing protocols include:

    Number ofnetwork layer devices along the path (hop count)

    Bandwidth

    Delay

    Load

    MTU

    Cost

    Routing protocols store the results of these metrics in a routing table.

    Interior vs. Exterior Routing Protocols

    http://www.ehow.com/facts_5453209_define-antivirus.htmlhttp://www.ehow.com/facts_5453209_define-antivirus.htmlhttp://www.tech-faq.com/network-layer.shtmlhttp://www.tech-faq.com/mtu.shtmlhttp://www.tech-faq.com/routing-table.shtmlhttp://www.tech-faq.com/routing-table.shtmlhttp://www.ehow.com/facts_5453209_define-antivirus.htmlhttp://www.ehow.com/facts_5453209_define-antivirus.htmlhttp://www.ehow.com/facts_5453209_define-antivirus.htmlhttp://www.tech-faq.com/network-layer.shtmlhttp://www.tech-faq.com/mtu.shtmlhttp://www.tech-faq.com/routing-table.shtmlhttp://www.ehow.com/facts_5453209_define-antivirus.htmlhttp://www.ehow.com/facts_5453209_define-antivirus.html
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    Some routing protocols are designed for use within an organization, while other routingprotocols are designed for use between organizations.

    The current lead Interior Gateway Protocol (IGP) is OSPF. Other Interior Gateway Protocolsinclude IS-IS, RIP, and EIGRP.

    The current lead Exterior Gateway Protocol is BGP. The current revision of BGP is BGP4. There

    are no other Exterior Gateway Routing protocols in current competition with BGP4.

    Distance Vector vs. Link State Routing ProtocolsRouting protocols such as RIP and EIGRP are Distance Vector routing protocols. These arecalled Distance Vector protocols because they base routing decisions on the "distance" of theremote destination in terms of the number ofnetwork layerhops which the packet will have totraverse.

    OSPF and IS-IS are Link State routing protocols. They are called Link State protocols becausethey base routing decisions on messages received from other routers in the internetwork whichgive information about state of the links connected to them.

    ---------------What Is an IP Address?

    An IP address is an address used to uniquely identify a device on an IP network. An IP networkis nothing but a connection of multiple computers forming a network. An IP address can begiven to any kind of network component that has to communicate over the network, such ascomputers, servers, routers, switches, etc. Any two computers, or any other network devices,cannot communicate with each other if they do not have an assigned IP address. They aredesigned to uniquely identify each network device and allow them to communicate with eachother, regardless of the physical location of the sender and receiver.

    Hence, an IP address is the unique identity of any network device where each one should have

    their own IP address defined. On the Internet, computers are recognized by their IP addressesonly. IP addresses have an equal significance as the postal addresses have for human beings. Canyou send a letter to anyone if you do not know where he/she lives? This should explain theimportance of an IP address.

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    An IP address is 32 (thirty two) bits in length, which can be divided into a network portion and ahost portion with the help of a subnet mask. It is represented in form of four octets, where 1 octet= 8 bits. Each octet is converted to a decimal format and is separated by a dot (.). For thisreason, an IP address is said to be expressed in a dotted decimal format.Examples of IP addresses in decimal format: 10.1.1.1, 255.255.255.255, 220.3.1.5

    The value in each octet ranges from 0 to 255 in decimal format. The dotted decimal format isused to make it easier for the humans to read and remember the numbers, but computers use IPaddresses in a binary format only.

    Example of an IP address in binary format: 10011101.11100010.10101110.11101000

    Public IP Address : It is a unique IP address assigned by IANA (Internet Assigned

    Network Authority). Duplication of the public IP addresses is impossible; hencethese addresses need to be bought.

    Summary: Every device on an TCP/IP network must have a unique IP address. IP addresses areassigned, either automatically by DHCP, or by manual configuration.

    Given that IP address must be unique for every computer attached to the internet,how is itpossible that we do not plug in IP addresses for the computer we want to connect?

    Well, every device connected to the internet must have a unique IP, it's true. And they'reassigned one of two ways: static or dynamic. But there's also a useful trick that lets multiplecomputers share a single IP address ... and that trick is called a router.

    Static IP addresses are exactly that: static or unchanging. They are assigned by your networkadministrator or ISP, and yes, you do have to configure the computer or other internet devicemanually to respond to that specific address.

    But, as you point out, most folks don't need to do that. So how do they get their IP addresses?

    Enter the dynamic IP address and "DHCP" or Dynamic Host Configuration Protocol.

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    Using DHCP (which is the default for Windows TCP/IP connections) the computer broadcasts aspecial request for an IP address to the network. An upstream device, commonly belonging toyour ISP, responds with an IP address that the computer then configures itself to use. Especiallywhen many computers aren't connected continuously, this allows the ISP to reuse the IPaddresses of computers that have disconnected from the internet.

    If you need your computer to be identifiable on the internet ... for example if you're running aweb server or want people to be able to connect to your machine, you'll probably need or use astatic IP address. On the other hand, if all you do is connect out to surf or read email, as mostusers do, then a dynamic IP address is the easiest to configure.

    Routers are devices that allow multiple computers to "share" a single IP address. The devicethat's connected to the internet is the router, and it has a unique IP address. The router can thenact as the DHCP server to the local network handing out local IP addresses to the computersconnected to it. As traffic flows across the router, it does the job of translating the IP addressesfrom the local addresses it has assigned, to the external IP address it was assigned, and routingthe right bits of data to the right computer ... hence the name.

    One of the many side effects of using a router is that it can be assigned a static address on the

    internet, d hand out dynamic IP addresses locally, vice versa, or any combination.

    It is done at Start, Settings, Control, Panel, Network, the Properties of the instance

    of the TCP/IP protocol bound to (associated with) the network adapter, IP Address

    Tab. They are known as static IP addresses. 192.168.0.1 is usually assigned to the

    computer with the Internet sharing software and 192.168.0.2, 192.168.0.3, etc. are

    usually assigned to the client computers. The subnet mask should be 255.255.255.0

    on all of the computers. You will need to enable DNS (domain name service) in the

    DNS Configuration tab and enter the IP addresses of your ISPs (Internet Service

    Provider) DNS servers. Most ISPs have a primary and secondary DNS server andthat info is usually provided in the paperwork the ISP sent you when you signed-up.

    It is also usually available on the ISPs web site. I do not like proxy servers. NATs

    (Network Address Translators) are easier to install. Discussion of other solutions

    starts at http://duxcw.com/faq/ics/waysshare.htm.

    Technically, a "public" address would be an address that anyone can use. Such as:

    192.168.x.y

    These public address that anyone can use are "classful" or based on older Class A,B,

    and C IP networks.

    These "public" ranges would be the 10.x.y.z network (/slash 8)

    172.16.x.y - 172.22.x.y (i could be wrong, off the top of my head)

    and 192.168.x.y (/slash 16)

    These are reserved and have no global significance.

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    Shown below is the Public IP Address Range & Private IP Address Range.

    Public IP Address Range:

    Class A(Netid.hostid.hostid.hostid) : 1.0.0.0 to 126.0.0.0Class B(Netid.Netid.hostid.hostid) : 128.0.0.0 to 191.0.0.0Class C(Netid.Netid.Netid.hostid) : 192.0.0.0 to 223.0.0.0Class D(Multicast) : 224.0.0.0 to 239.0.0.0Class E(For Research) : 240.0.0.0 to 255.0.0.0

    Private IP Address Range:

    Class A(/8) : 10.0.0.0 to 10.255.255.255Class B(/12) : 172.16.0.0 to 172.31.255.255Class C(/16) : 192.168.0.0 to 192.168.255.255

    Note:

    /8 = First 8 Bits are used for Network ID/12 = First 12 Bits are used for Network ID/16 = First 16 Bits are used for Network ID

    Application layer: Provides a means for the user to access information on the network through anapplication. This layer is the main interface for the user to interact with the application and therefore thenetwork.

    The application layer is the OSI layer closest to the end user, which means that both the OSIapplication layer and the user interact directly with the software application. This layer interacts withsoftware applications that implement a communicating component. Such application programs fall outsidethe scope of the OSI model.

    Application layer functions typically includeidentifying communication partners,determining resource availability,and synchronizing communication.

    When identifying communication partners, the application layer determines the identity andavailability of communication partners for an application with data to transmit.

    When determining resource availability, the application layer must decide whether sufficientnetwork resources for the requested communication exist.

    In synchronizing communication, all communication between applications requires cooperationthat is managed by the application layer.

    Some examples of application layer implementations include Telnet, File Transfer Protocol (FTP),and Simple Mail Transfer Protocol (SMTP).

    Or

    The Application Layer is the highest layer of the OSI architecture, the purpose of which is toserve as a window between correspondent application processes so that they may exchangeinformation on the open environment. The progams which use the Application Layer are knownas Application Processes. A user program may interface directly with the Presentation Layerinwhich case it must include protocol modules to initialise communication with peer application

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    processes, establish the appropriate Presentation context and transfer files or messages.Alternatively, the user process may include available modules which suppport commonlyrequired application related services. Such modules are referred to as Application SpecificElements and are defined as an integrated set of functions which together provide one or moreapplication related communication capabilities. These capabilities are defined by a protocol in avery similar manner to that used to specify a service provided by the layer below. The protocolmay specify direct use of presentation layer services and/or those provided by other ASEs. Thegrouping of a user process (or application entity), relevant ASEs and interfaces between them isknown as an application process.

    Application Layer protocols are classified into Common Application Specific Elements (CASE)and Specific Application Specific Elements (SASE). CASE elements are commonly required byuser elements and SASEs, whereas SASEs are only included in an application process when their

    particular service is specifically required. For more information on SASEs Group Xs project canbe consulted (LINK).There are four CASEs currently defined. These are...

    1. Association Control ACSE,

    2. Reliable TransferRTSE,

    3. Remote Operations ROSE and

    4. Recovery CCR.

    ACSE (Padraig Butler) enables users to establish or terminate an association betweenapplication processes.

    RTSE (Caroline O'Reilly) enables reliable transfer of information between peers.

    ROSE (Emma Kilcoyne) enables users to initate operations at a remote site.

    CCR(Dave Barry) enables users to recover from failure during execution of a task.

    1.2 Presentation layer: Manages the presentation of the information in an ordered and meaningful

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    manner. This layer's primary function is the syntax and semantics of the data transmission. It convertslocal host computer data representations into a standard network format for transmission on the network.On the receiving side, it changes the network format into the appropriate host computer's format so thatdata can be utilized independent of the host computer. ASCII and EBCDIC conversions, cryptography,and the like are handled here.

    The presentation layer provides a variety of coding and conversion functions that are applied toapplication layer data. These functions ensure that information sent from the application layer of one

    system would be readable by the application layer of another system. Some examples of presentationlayer coding and conversion schemes include common data representation formats, conversion ofcharacter representation formats, common data compression schemes, and common data encryptionschemes.

    Common data representation formats, or the use of standard image, sound, and video formats,enable the interchange of application data between different types of computer systems. Using differenttext and data representations, such as EBCDIC and ASCII, uses conversion schemes to exchangeinformation with systems. Standard data compression schemes enable data that is compressed. orencrypted at the source device to be properly decompressed, or deciphered at the destination.

    Presentation layer implementations are not typically associated with a particular protocol stack.Some well-known standards for video include QuickTime and Motion Picture Experts Group (MPEG).

    QuickTime is an Apple Computer specification for video and audio, and MPEG is a standard for videocompression and coding.Among the well-known graphic image formats are Graphics Interchange Format (GIF), Joint PhotographicExperts Group (JPEG), and Tagged Image File Format (TIFF). GIF is a standard for compressing andcoding graphic images. JPEG is another compression and coding standard for graphic images, and TIFFis a standard coding format for graphic images.

    Presentation Layer Functions

    Here are some of the specific types of data handling issues that the presentation layerhandles:

    Translation: Networks can connect very different types of computers together:

    PCs, Macintoshes, UNIX systems, AS/400 servers and mainframes can all existon the same network. These systems have many distinct characteristics andrepresent data in different ways; they may use different character sets forexample. The presentation layer handles the job of hiding these differencesbetween machines.

    Compression: Compression (and decompression) may be done at the

    presentation layer to improve the throughput of data. (There are some whobelieve this is not, strictly speaking, a function of the presentation layer.)

    Encryption: Some types of encryption (and decryption) are performed at thepresentation layer. This ensures the security of the data as it travels down theprotocol stack. For example, one of the most popular encryption schemes that isusually associated with the presentation layer is the Secure Sockets Layer (SSL)protocol. Not all encryption is done at layer 6, however; some encryption is oftendone at lower layers in the protocol stack, in technologiessuch as IPSec.

    Or

    We deal with the following aspects of the presentation layer:

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    OSI Definition of Presentation Layerand ISO Presentation ServiceA quick run through the OSI Definition of the Presentation Layer, outlining among otherthings the services provided by the presentation layer and the functions of thepresentation layer. The ISO Presentation Service is covered in detail.

    ISO Presentation Protocol and ConceptsPresentation Layer Concepts and the ISO Presentation Layer. There is no mention of dataencryption here because the actual presentation protocol is concerned only with thesyntax of messages during their transfer across the network.

    Abstract Syntax and Transfer SyntaxApplication exchanges involve transmitting data structures which may be complicated.OSI introduced the notion ofabstract syntax and transfer syntax. Included is a

    comparisonbetween BER (Basic Encoding Rules) and Sun Microsystems' XDR(External Data Representation).

    Data Encryption and Data CompressionData Encryption is used to prevent listening or masquerading. In the context of the OSIReference Model, the most appropriate layer to perform such encryption is thepresentation layer. Data compression is done if required.

    Summarizes the features of peer-to-peer and server-based networks:

    Feature Peer-to-peer Network Server-based Network

    Size Good for up to 10 users

    Limited only by server andnetwork hardware

    Security

    Users are responsible for theirown security

    Offers extensive user

    security

    Administration

    Is administered by the user of

    each computer

    Is centrally administered

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    Peer to Peer everybody is equal, security is slack, and you can only have a few

    comps on network

    server based offers better security, monitor users, more technical and time

    consuming to set-up, less likely to cause problems if set-up correctly, any amount of

    comps etc....

    In a Peer to peer network, all nodes are equal. They are both client and server. Most

    P2P networks use a mesh topology.

    In the client/server model, the data is centralised with all data residing on a single

    node (the server) clients request the data and the server sends it. Data on one

    client must pass through the server to be available to another client. Most

    client/server networks use a star topology.

    Client Server has the advantage of centralised management and data integrity

    whilst P2P has the advantage of faster data transfer and avoids network

    bottlenecks.

    What Is DHCP?DHCP, the Dynamic Host Configuration Protocol, describes the means by which a system canconnect to a network and obtain the necessary information for communication upon thatnetwork. FreeBSD versions prior to 6.0 use the ISC (Internet Systems Consortium) DHCP client

    (dhclient(8)) implementation. Later versions use the OpenBSD dhclient taken fromOpenBSD 3.7. All information here regarding dhclient is for use with either of the ISC orOpenBSD DHCP clients. The DHCP server is the one included in the ISC distribution.

    29.5.2 What This Section CoversThis section describes both the client-side components of the ISC and OpenBSD DHCP clientand server-side components of the ISC DHCP system. The client-side program, dhclient,comes integrated within FreeBSD, and the server-side portion is available from thenet/isc-dhcp3-server port. The dhclient ( 8), dhcp -options (5), and dhclient.conf (5) manual pages, inaddition to the references below, are useful resources.

    29.5.3 How It WorksWhen dhclient, the DHCP client, is executed on the client machine, it begins broadcastingrequests for configuration information. By default, these requests are on UDP port 68. The serverreplies on UDP 67, giving the client an IP address and other relevant network information suchas netmask, router, and DNS servers. All of this information comes in the form of a DHCPlease and is only valid for a certain time (configured by the DHCP server maintainer). In thismanner, stale IP addresses for clients no longer connected to the network can be automaticallyreclaimed.

    http://www.freebsd.org/cgi/man.cgi?query=dhclient&sektion=8http://www.freebsd.org/cgi/url.cgi?ports/net/isc-dhcp3-server/pkg-descrhttp://www.freebsd.org/cgi/url.cgi?ports/net/isc-dhcp3-server/pkg-descrhttp://www.freebsd.org/cgi/url.cgi?ports/net/isc-dhcp3-server/pkg-descrhttp://www.freebsd.org/cgi/man.cgi?query=dhclient&sektion=8http://www.freebsd.org/cgi/man.cgi?query=dhcp-options&sektion=5http://www.freebsd.org/cgi/man.cgi?query=dhclient.conf&sektion=5http://www.freebsd.org/cgi/man.cgi?query=dhclient&sektion=8http://www.freebsd.org/cgi/url.cgi?ports/net/isc-dhcp3-server/pkg-descrhttp://www.freebsd.org/cgi/url.cgi?ports/net/isc-dhcp3-server/pkg-descrhttp://www.freebsd.org/cgi/man.cgi?query=dhclient&sektion=8http://www.freebsd.org/cgi/man.cgi?query=dhcp-options&sektion=5http://www.freebsd.org/cgi/man.cgi?query=dhclient.conf&sektion=5
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    DHCP clients can obtain a great deal of information from the server. An exhaustive list may befound in dhcp - options ( 5).

    Short forDynamic HostConfiguration Protocol, aprotocol for assigningdynamicIP addresses

    to devices on a network. With dynamic addressing, a device can have a different IP addressevery time it connects to the network. In some systems, the device's IP address can even changewhile it is still connected. DHCP also supports a mix of static and dynamic IP addresses.

    Dynamic addressing simplifies network administration because the software keeps track of IPaddresses rather than requiring an administrator to manage the task. This means that a newcomputer can be added to a network without the hassle of manually assigning it a unique IPaddress. Many ISPs use dynamic IP addressing fordial-up users.

    Attenuation is a general term that refers to any reduction in the strength of a signal.Attenuation occurs with any type of signal, whether digital or analog. Sometimescalled loss, attenuation is a natural consequence of signal transmission over longdistances. The extent of attenuation is usually expressed in units called decibels

    (dBs).

    Attenuation and distortionAs a signal travels from one device to another it has two problems to overcome. The first is thatit gets weaker the further it travels, because some of its energy is absorbed by the transmissionmedium. This effect is known as attenuation. The extent of attenuation depends on the distanceit has to travel and on the type of medium it is travelling through. An amplifier can be used toboost the signal power at the transmitter and receiver, and if necessary at various points in thetransmission link, so that signal power can be maintained at a usable level.

    The second problem is that the signal can become distorted by external influences as it travelsalong the communication path. This can be caused by other signals travelling in the vicinity, or

    by waves of energy such as solar energy, lightning, and pulses of energy from electricalmachinery. You might have come across instances of distortion in your own domesticequipment. For example, I have a small TV in my bedroom and when I use my hairdryer nearbyI can see spots and lines on the TV screen that are caused by the electromagnetic energygenerated by the motor in the hairdryer. If I place my mobile phone next to my radio I often hearbeeps on my radio as the phone sends signals to the phone network.

    Unless distortion can be removed from the signal at the receiving end then any amplification toovercome the problems of attenuation will also amplify any distortion in the received signal.Binary signals are quite resistant to distortion because they represent only two states that canusually be distinguished quite easily from any unwanted effects.

    TCP Header Format

    TCP segments are sent as internet datagrams. The Internet Protocol header carries severalinformation fields, including the source and destination host addresses [2]. A TCP headerfollows the internet header, supplying information specific to the TCP protocol. This divisionallows for the existence of host level protocols other than TCP.

    Source Port and Destination Port

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    Sequence Number - The number assigned to the first byte of data in the current message

    Acknowledgment Number - Contains the sequence number of the next byte of data thesender of this packet expects from the other host

    Data Offset - Indicates the number of 32-bit words in the TCP header

    Reserved - For future use Flags - Variety of control information, including SYN, ACK and FIN bits

    Window - Size of the sender's receive window

    Checksum - Error checking

    Urgent Pointer - Points to the first urgent data byte in the packet

    The TCP header format

    16 16

    Source Port Destination Port

    Sequence Number

    Acknowledgement Number

    Data offset Reserved Flags Window

    Checksum Urgent Pointer

    Option + Padding

    Data

    Source Port: 16 bits

    The source port number.

    Destination Port: 16 bits

    The destination port number.

    Sequence Number: 32 bits

    The sequence number of the first data octet in this segment (except

    when SYN is present). If SYN is present the sequence number is the

    initial sequence number (ISN) and the first data octet is ISN+1.

    Acknowledgment Number: 32 bits

    If the ACK control bit is set this field contains the value of the

    next sequence number the sender of the segment is expecting to

    receive. Once a connection is established this is always sent.

    Data Offset: 4 bits

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    The number of 32 bit words in the TCP Header. This indicates where

    the data begins. The TCP header (even one including options) is an

    integral number of 32 bits long.

    Reserved: 6 bits

    Reserved for future use. Must be zero.

    Control Bits: 6 bits (from left to right):URG: Urgent Pointer field significant

    ACK: Acknowledgment field significant

    PSH: Push Function

    RST: Reset the connection

    SYN: Synchronize sequence numbers

    FIN: No more data from sender

    Window: 16 bits

    The number of data octets beginning with the one indicated in the

    acknowledgment field which the sender of this segment is willing to

    accept.

    Checksum: 16 bitsThe checksum field is the 16 bit one's complement of the one's

    complement sum of all 16 bit words in the header and text. If a

    segment contains an odd number of header and text octets to be

    checksummed, the last octet is padded on the right with zeros to

    form a 16 bit word for checksum purposes. The pad is not

    transmitted as part of the segment. While computing the checksum,

    the checksum field itself is replaced with zeros.

    The checksum also covers a 96 bit pseudo header conceptually

    prefixed to the TCP header. This pseudo header contains the Source

    Address, the Destination Address, the Protocol, and TCP length.

    This gives the TCP protection against misrouted segments. This

    information is carried in the Internet Protocol and is transferredacross the TCP/Network interface in the arguments or results of

    calls by the TCP on the IP.

    +--------+--------+--------+--------+

    | Source Address |

    +--------+--------+--------+--------+

    | Destination Address |

    +--------+--------+--------+--------+

    | zero | PTCL | TCP Length |

    +--------+--------+--------+--------+

    The TCP Length is the TCP header length plus the data length in

    octets (this is not an explicitly transmitted quantity, but is

    computed), and it does not count the 12 octets of the pseudoheader.

    Urgent Pointer: 16 bits

    This field communicates the current value of the urgent pointer as a

    positive offset from the sequence number in this segment. The

    urgent pointer points to the sequence number of the octet following

    the urgent data. This field is only be interpreted in segments with

    the URG control bit set.

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    Options: variable

    Options may occupy space at the end of the TCP header and are a

    multiple of 8 bits in length. All options are included in the

    checksum. An option may begin on any octet boundary. There are two

    cases for the format of an option:

    Case 1: A single octet of option-kind.

    Case 2: An octet of option-kind, an octet of option-length, and

    the actual option-data octets.

    The option-length counts the two octets of option-kind and

    option-length as well as the option-data octets.

    Note that the list of options may be shorter than the data offset

    field might imply. The content of the header beyond the

    End-of-Option option must be header padding (i.e., zero).

    A TCP must implement all options.

    Currently defined options include (kind indicated in octal):

    Kind Length Meaning

    ---- ------ -------

    0 - End of option list.

    1 - No-Operation.

    2 4 Maximum Segment Size.

    Specific Option Definitions

    End of Option List

    +--------+

    |00000000|+--------+

    Kind=0

    This option code indicates the end of the option list. This

    might not coincide with the end of the TCP header according to

    the Data Offset field. This is used at the end of all options,

    not the end of each option, and need only be used if the end of

    the options would not otherwise coincide with the end of the TCP

    header.

    No-Operation

    +--------+

    |00000001|

    +--------+

    Kind=1

    This option code may be used between options, for example, to

    align the beginning of a subsequent option on a word boundary.

    There is no guarantee that senders will use this option, so

    receivers must be prepared to process options even if they do

    not begin on a word boundary.

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    Maximum Segment Size

    +--------+--------+---------+--------+

    |00000010|00000100| max seg size |

    +--------+--------+---------+--------+

    Kind=2 Length=4

    Maximum Segment Size Option Data: 16 bits

    If this option is present, then it communicates the maximum

    receive segment size at the TCP which sends this segment.

    This field must only be sent in the initial connection request

    (i.e., in segments with the SYN control bit set). If this

    option is not used, any segment size is allowed.

    Padding: variable

    The TCP header padding is used to ensure that the TCP header ends

    and data begins on a 32 bit boundary. The padding is composed of

    zeros.