Semester 2 chapter 9 the tcp ip protocol suite
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Semester 2 Chapter 9 The TCP/IP Protocol Suite. Paul Flynn. Lesson Overview. How TCP/IP operates to ensure communication across any set of interconnected networks. Learn about parts of the TCP/IP protocol stack that support: File transfer (FTP, TFTP), e-mail,

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Semester 2 Chapter 9 The TCP/IP Protocol Suite

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Semester 2 chapter 9 the tcp ip protocol suite

Semester 2 Chapter 9 The TCP/IP Protocol Suite

Paul Flynn

Lesson overview

Lesson Overview

  • How TCP/IP operates to ensure communication across any set of interconnected networks.

    • Learn about parts of the TCP/IP protocol stack that support:

      • File transfer (FTP, TFTP),

      • e-mail,

      • Reliable (TCP) and unreliable (UDP) transport layer protocols,

      • Connectionless datagram (packet) delivery at the network layer,

      • ICMP provides control and message functions at the network layer,

      • ARP and RARP.

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Tcp ip


  • Developed by the Defence Advanced Research Projects Agency (DARPA).

  • Later included with the Berkeley Software Distribution of UNIX.

  • Now the de facto standard for internetwork communications.

  • Serves as the transport protocol for the Internet.

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9 1 1 the internet tcp ip protocols and the osi model

9.1.1 The Internet TCP/IP protocols and the OSI model

  • OSI Layers 7,6 & 5 are rolled into 1 application layer

  • The Transport layer in both models perform basically the same function

  • OSI layers 2 & 1 are combined into 1 Network Access layer

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9 1 2 tcp ip protocol stack and the application layer

9.1.2 TCP/IP protocol stack and the application layer

  • DNS - Domain Name System

  • WINS - Windows Internet Naming System

  • NFS - Network File System (The standard UNIX file system)

  • POP3 - Post Office Protocol (An e-mail standard)

  • SMTP - Simple Mail Transfer Protocol

  • SNMP - Simple Network Management Protocol

  • FTP - File Transfer Protocol (Upload/Download files from the ‘net)

  • TFTP - Trivial File Transfer Protocol

  • HTTP - The Internet standard for web browsing

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Semester 2 chapter 9 the tcp ip protocol suite

9.1.2 TCP/IP protocol stack and the application layer

  • Other Application Layer protocols used for troubleshooting a network include:

    • Telnet - A standard terminal emulation protocol

    • PING - Packet InterNet Groper

    • Traceroute - Traces the path of a packet from the source to the receiver.

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9 1 3 tcp ip protocol stack and the transport layer

9.1.3 TCP/IP protocol stack and the transport layer

  • The transport layer provides two protocols:

    • TCP (Transport Control Protocol)

      • Provides reliable, connection-oriented communications between 2 hosts.

      • TCP requires more network overhead because data is acknowledged as it is received.

  • UDP (User Datagram Protocol)

    • UDP is faster but less reliable, because the recipient does not acknowledge the data as it is received.

    • Communication reliability is left to the Application Layer

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9 1 4 tcp segment format

9.1.4 TCP segment format

  • source port -- the number of the calling port

  • destination port -- the number of the called port

  • sequence number -- the number used to ensure correct sequencing of the arriving data

  • acknowledgment number -- the next expected TCP octet

  • HLEN -- the number of 32-bit words in the header

  • reserved -- set to 0

  • code bits -- the control functions (e.g. setup and termination of a session)

  • window -- the number of octets that the sender is willing to accept

  • checksum -- the calculated checksum of the header and data fields

  • urgent pointer -- indicates the end of the urgent data

  • option -- one currently defined: maximum TCP segment size

  • data -- upper-layer protocol data

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9 1 4 udp segment format

9.1.4 UDP segment format

  • Application layer protocols provide for reliability.

  • UDP uses no windowing or acknowledgments.

  • Designed for applications that do not need to put sequences of segments together.

  • Protocols that use UDP are:

    • TFTP

    • SNMP

    • Network File System (NFS)

    • Domain Name System (DNS)

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9 1 5 tcp and udp port numbers

9.1.5 TCP and UDP port numbers

  • Both TCP and UDP use port numbers for communication between hosts.

    • Port numbers are similar to phone numbers

    • Transport layer services can be “called” by their port number.

  • EG When a Host wants to transfer a file using FTP

    • Uses TCP port 21 to establish and control the connection

    • Uses TCP port 20 to transfer the data

    • TCP ports 20 & 21 are called “Well Known Port Numbers” because applications expect to find FTP services on these ports.

  • Other “Well Known” Port numbers are:

    • TCP Port 23 - Telnet

    • TCP Port 25 - SMTP (email)

    • TCP Port 53 - DNS

    • TCP Port 80 - HTTP web services

    • UDP Port 53 - DNS

    • UDP Port 69 - TFTP

    • UDP Port 161 - SNMP

Request For Comment 1700 defines “Well Known Port Numbers”

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9 1 6 tcp three way handshake open connection

9.1.6 TCP three-way handshake/open connection

  • For TCP to establish a reliable connection between 2 hosts.

    • Uses a “Three Way Handshake”

    • Transmits 3 packets before the actual data

    • The 2 Hosts synchronise their “Initial Sequence Number” (ISN)

    • Ensures that the communications are assembled in the correct order and no missing packets exist.

  • The process occurs by

    • Host 1 sends a SYN packet to Host 2 (1st data packet)

    • Host 2 ACK the packet from Host 1 (2nd data packet)

    • Host 2 includes its’ own SYN data for Host 1 (2nd data packet)

    • Host 1 ACK packet from Host 2 (3rd data packet)

  • It is call the 3 way handshake because only 3 packets are exchanged

    • The SYN packet from Host 2 also serves as the acknowledgment to the SYN packet from Host 1

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9 1 7 tcp simple acknowledgment and windowing

9.1.7 TCP simple acknowledgment and windowing

  • TCP “Sliding Windows” control the flow and efficiency of communication

    • Quite simply, once the window fills with data, the destination host sends an ACK for packets received in that window

    • The window slides over in order to select new packets.

  • TCP window sizes can change during the life of the connection so that the window can be

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9 2 1 tcp ip and the internet layer

9.2.1TCP/IP and the Internet Layer

  • The Internet layer of the TCP/IP stack corresponds to the network layer of the OSI model.

  • Several protocols operate at the TCP/IP Internet layer that corresponds to the OSI network layer:

    • IP -- provides connectionless, best-effort delivery routing of datagrams; is not concerned with the content of the datagrams; looks for a way to move the datagrams to their destination

    • ICMP -- provides control and messaging capabilities

    • ARP -- determines the data link layer address for known IP addresses

    • RARP -- determines network addresses when data link layer addresses are known

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9 2 2 t he ip datagram

9.2.2The IP datagram

  • An IP datagram contains an IP header and data, and is surrounded by the Media Access Control (MAC) layer header and MAC layer trailer. One message may be transmitted as a series of datagrams that are reassembled into the message at the receiving location.

  • VERS -- version number

  • HLEN -- header length, in 32-bit words

  • type of service -- how the datagram should be handled

  • total length -- total length (header + data)

  • identification, flags, flag offset -- provides fragmentation of datagrams to allow differing MTUs in the internetwork

  • TTL -- Time-To-Live

  • protocol -- the upper-layer (Layer 4) protocol sending the datagram

  • header checksum -- an integrity check on the header

  • source IP address and destination IP address -- 32-bit IP addresses

  • IP options -- network testing, debugging, security, and other options

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9 2 2 t he ip datagram1

9.2.2The IP datagram

  • The protocol field determines the Layer 4 protocol being carried within an IP datagram. Although most IP traffic uses TCP, other protocols can also use IP.

  • Each IP header must identify the destination Layer 4 protocol for the datagram.

  • Transport layer protocols are numbered, similarly to port numbers.

  • IP includes the protocol number in the protocol field

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9 2 3 internet control message protocol icmp

9.2.3Internet Control Message Protocol (ICMP)

  • Provides message control and error reporting services between 2 TCP/IP hosts or between a host server and a gateway to the Internet.

    • The PING utility uses ICMP messages to check connections between 2 points.

  • EG: A router receives a packet that it is unable to deliver to its final destination.

  • The router sends an ICMP unreachable message to the source.

  • The message might be undeliverable because there is no known route to the destination.

  • An echo reply is a successful reply to a ping command.

  • Results could include other ICMP messages, such as host unreachable and timeouts.

  • How many of you have sent an email with the wrong address and it comes back to you with the message “host unknown”?

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9 2 4 how arp works

9.2.4How ARP works

  • ARP maps IP addresses to MAC addresses.

    • The source of the network packet sends the information to the destination.

    • Unique MAC addresses reference the end points in the exchange.

    • Networked devices maintain details of MAC and IP addresses of other devices on the network.

    • This is called an ARP table or cache

    • Maintained in RAM

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9 2 4 how arp works1

9.2.4How ARP works

  • A computer transmits a packet on the network.

  • It checks its’ ARP cache for an IP to MAC address mapping

  • If source finds an appropriate IP to MAC mapping, the source uses the IP and MAC address to encapsulate the data that it is ready to transmit.

  • Source computer sends the packet directly to the destination.

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9 2 4 how arp works2

9.2.4How ARP works

  • The IP address is listed first, the MAC address next, followed by information about whether the entry is static or dynamic.

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9 2 4 how arp works3

9.2.4How ARP works

  • If a source computer cannot locate an IP to MAC address mapping in its’ ARP table, it must obtain the correct mapping.

  • Source initiates an ARP request to all hosts to gain the destinations’ MAC address.

  • The one host that sees that the ARP packet is meant for its’ IP address responds to the ARP request.

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How rarp works

How RARP works

  • RARP is similar to ARP in that computers use it to bind MAC addresses to IP addresses.

  • RARP is used by Diskless Workstations which have a MAC address burned into their network cards but no IP address.

  • A clients IP configuration is stored on a RARP server

  • RARP servers maintain a table of MAC and IP address mapping for RARP clients.

  • During the boot process, a RARP client will call the RARP server to obtain their IP configuration.

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Semester 2 chapter 9 the tcp ip protocol suite

The preceding presentation was put together using the Cisco curriculum and the CCNA Guide to Cisco Networking Fundamentals by Kurt Hudson and Kelly Cannon.

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