tcp ip

TCP/IPTCP/IP

Origins of TCP/IPOrigins of TCP/IP

• Transmission Control Protocol/Internet Protocol (TCP/IP)– Protocol suite whose invention and evolution resulted from

a coordinated effort by the United States Department of Defense (DOD)

• Advanced Research Projects Agency (ARPA)– DOD branch responsible for creation and proliferation of

the Internet and TCP/IP protocol suite– Advanced Research Projects Agency Network

(ARPANET)• Original name of the Internet

TCP/IP is the Internet Communication ProtocolTCP/IP is the Internet Communication Protocol

• A communication protocol is a description of the rules computers must follow to communicate with each other.

• The Internet communication protocol defines the rules for computer communication over the Internet.

• TCP/IP defines how electronic devices (like computers) should be connected to the Internet, and how data should be transmitted between them.

TCP/IP TCP/IP

• TCP/IP is TCP and IP working together.

• TCP takes care of the communication between your application software (i.e. your browser) and your network software.

• IP takes care of the communication with other computers.

TCP/IPTCP/IP

• TCP is responsible for breaking data down into IP packets before they are sent, and for assembling the packets when they arrive.

• IP is responsible for sending the packets to the correct destination.

Your Browser and Your Server Use TCP/IPYour Browser and Your Server Use TCP/IP

• Internet browsers and Internet servers use TCP/IP to connect to the Internet.

• Your browser uses TCP/IP to access Internet servers, and servers use TCP/IP to send HTML back to your browser.

Your E-Mail Uses TCP/IPYour E-Mail Uses TCP/IP

• Your e-mail program uses TCP/IP to connect to the Internet for sending and receiving e-mails.

Your Internet Address is TCP/IPYour Internet Address is TCP/IP

• Your Internet address "222.48.162.2" is a part of the standard TCP/IP protocol (and so is your domain name "www.myroomplace.com").

Overview of the TCP/IP Protocol Overview of the TCP/IP Protocol SuiteSuite

• Four layers of the TCP/IP protocol suite :– Application– Transport– Internetwork– Network Interface

• Series of documents called Requests for Comments (RFCs) define, describe, and standardize implementation and configuration of the TCP/IP protocol suite– The Internet Network Information Center

(InterNIC) is responsible for maintaining these standards

Overview of the TCP/IP Protocol Overview of the TCP/IP Protocol SuiteSuite

Figure 3-1: Protocol architecture comparison

• Protocols at the TCP/IP Application layer include:– File Transfer Protocol (FTP)– Trivial File Transfer Protocol (TFTP)– Network File System (NFS)– Simple Mail Transfer Protocol (SMTP)– Terminal emulation protocol (telnet)– Remote login application (rlogin)– Simple Network Management Protocol (SNMP)– Domain Name System (DNS)– Hypertext Transfer Protocol (HTTP)

Application LayerApplication Layer• Protocols that exist at this layer include:

– File Transfer Protocol (FTP)• Moves files between devices.• Performs basic interactive file transfers between hosts.

– Trivial File Transfer Protocol (TFTP)• File transfer utility used on the Internet. TFTP uses UDP (User

Datagram Protocol*2) to transfer files and is therefore less reliable than FTP which uses TCP in transferring files.

• User Datagram Protocol that operates at the Transport layer and transports data unreliably over IP. Sometimes known as connectionless communication as the messages are sent without expectation of acknowledgment. – No connection negotiation process– Faster than TCP

Application LayerApplication Layer– Network File System (NFS)

• enable transparent access to remote network resources– Simple Mail Transfer Protocol (SMTP)

• Supports basic message delivery services

• Provides electronic mail services– Terminal emulation protocol (telnet)

• Serves as a terminal emulation protocol• Enables users to execute terminal sessions with

remote hosts – Remote login application (rlogin)

• Utility that allows remote computers to connect to other computers or devices

Application LayerApplication Layer

– Simple Network Management Protocol (SNMP)• Protocol that provides network administrators the ability to centrally control and

monitor the network.

• A protocol that is used to collect management information from network devices.

– Domain Name System (DNS)• Also called name service; this application maps IP addresses to the names

assigned to network devices.

– Hypertext Transfer Protocol (HTTP)• Protocol used for communication on the World Wide Web.• The protocol used by Web browsers and Web servers to

transfer files, such as text and graphic files.

Transport LayerTransport Layer

• Two protocols reside at this layer:– TCP– User Datagram Protocol (UDP)

• Ports• connection point, usually for network cable, on a device e.g. hub, router, bridge

and switch

– Both TCP and UDP use port numbers for communication between hosts

– Well Known Port Numbers• TCP and UDP ports from 0 through 1023 on which client

applications expect to find common Internet services

Transport LayerTransport Layer

• Performs end-to-end packet delivery, reliability, and flow control

• Protocols:– TCP provides reliable, connection-oriented

communications between two hosts• Requires more network overhead

– UDP provides connectionless datagram services between two hosts

• Faster but less reliable

• Reliability is left to the Application layer

Well Known TCP and UDP Port Well Known TCP and UDP Port Numbers from RFC 1700Numbers from RFC 1700

• TCP port 20 – FTP data transfer

• TCP port 21 – FTP control port

• TCP port 23 – Telnet

• TCP port 25 – SMTP

• TCP & UDP port 53 – DNS

• TCP port 80 – HTTP Web services

TCP Three-Way HandshakeTCP Three-Way Handshake

• TCP three-way handshake– Establishes a reliable connection between two points

– TCP transmits three packets before the actual data transfer occurs

– Before two computers can communicate over TCP, they must synchronize their initial sequence numbers (ISN)

– A reset packet (RST) indicates that a TCP connection is to be terminated without further interaction


• Before two computers can communicate over TCP, they must synchronize their initial sequence numbers (ISN)

• When a synchronization request is sent, it is abbreviated SYN

• When an acknowledgement is sent, the abbreviation is ACK

– Exceptional acknowledgment

• Acknowledgment number refers to the sequence number refers to the sequence number expected next

Internetwork LayerInternetwork Layer

• Four main protocols function at this layer:– Internet Protocol (IP)– Internet Control Message Protocol (ICMP)

• Uses eight different message types to manage 11 different aspects of IP communications

– Address Resolution Protocol (ARP)• * Protocol that works at the Internetwork layer of the TCP/IP networking model• Resolves a known IP address to an unknown MAC address• A routed protocol • Maps IP addresses to Mac address• ARP tables contains the MAC and IP addresses of other devices on the network

– Reverse Address Resolution Protocol (RARP)• Protocol used to resolve the clients’ unknown IP address to the clients MAC

address.• In the case of a diskless workstation, a source host will know its MAC address but

not its IP address


• ARP (continued)– When a computer transmits a frame to a

destination on the local network• It checks the ARP cache for an IP to MAC address

mapping for the destination node

• ARP request– If a source computer cannot locate an IP to MAC

address mapping in its ARP table• It must obtain the correct mapping


• ARP request (continued)– A source computer broadcasts an ARP request to

all hosts on the local segment• Host with the matching IP address responds this

request

• ARP request frame– See Figure 3-7

• ARP cache life– Source checks its local ARP cache prior to

sending packets on the local network


• Reverse Address Resolution Protocol (RARP) ..Continued– Similar to ARP– Used primarily by diskless workstations

• Which have MAC addresses burned into their network cards but no IP addresses

– Client’s IP configuration is stored on a RARP server


• RARP request frame– See Figure 3-8

• RARP client– Once a RARP client receives a RARP reply, it configures

its IP networking components• By copying its IP address configuration information into its local

RAM

• ARP and RARP compared– ARP is concerned with obtaining the MAC address of

other clients– RARP obtains the IP address of the local host


• The Ping utility– Packet Internet Groper (Ping) utility verifies

connectivity between two points– Uses ICMP echo request/reply messages

Network Interface LayerNetwork Interface Layer

• Plays the same role as the Data Link and Physical layers of the OSI model

• The MAC address, network card drivers, and specific interfaces for the network card function at this level of the TCP/IP protocol stack

• No specific IP functions exist at this layer because the layer’s focus is on communication with the network card and other networking hardware

Understanding Frame TransmissionUnderstanding Frame Transmission

• Each host on a segment evaluates the frame– To determine whether the listed destination MAC address

matches its own or is a broadcast to all hosts• The host makes a copy of the frame and sends the

original along the network path• On the destination host, frames are sent up the

TCP/IP stack– Removing each layer header information

• For a packet to be routed on a TCP/IP internetwork– An IP address and MAC address are required for both the

source and destination hosts

Routers on the NetworkRouters on the Network

• A router requires: – An IP address for every network segment to which it is

connected– A separate network interface or port for each network

segment

• Computers send frames to destinations that are not on their segment to the router (default gateway)

• The router must determine which subnet should receive the frame– The router references its routing table

Chapter SummaryChapter Summary

• TCP/IP is not limited to transmission control and Internet protocols

• TCP/IP was started by the Defense Advanced Research Projects Agency (DARPA)

• TCP/IP maps to a four-layer network model: Application, Transport, Internetwork, and Network Interface

• The Application layer in the TCP/IP model covers the Application, Presentation, and Session layers of the OSI reference model


• The TCP and UDP protocols reside at the Transport layer of the TCP/IP networking model

• Both TCP and UDP use port numbers from 1 to 65,535 to establish their communications between two points

• The Internet Protocol (IP) resides at the Internetwork layer and provides the logical address that can be passed through a router

• You can use the Ping utility with IP and ICMP to diagnose and troubleshoot network connections


• Address Resolution Protocol (ARP) and Reverse ARP (RARP) reside in the Internetwork layer

• The MAC address is the final leg of communication between hosts

• Routing tables can be created manually and dynamically

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