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Chapter Overview

TCP/IP DoD model

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Network Layer Protocols

Responsible for end-to-end communications on an internetwork

Contrast with data-link layer protocols, which provide communications on the same local area network (LAN)

TCP/IP is everywhere with networks

Web pages using TCP/IP Database access can use TCP/IP It started with DOD (tax payer’s $$)

In 1973 it is TCP/IP In 1978 they became TCP and IP (two

protocols) Mostly done at UC Berkeley and shipped

with its version of UNIX

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DoD model, OSI model and protocols

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Port Numbers and Sockets A port number refers to a specific

application or process running on a computer.

A socket is a combination of a port number and an IP address.

The Internet Assigned Numbers Authority (IANA) assigns well-known port numbers to common Internet applications.

The most commonly used port numbers are listed in the Services file on computers running TCP/IP.

Process/Application Apps and Protocols

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Port Protocol Description23 Telnet Terminal Emulation (Telephone network)21 FTP Allows file transfers between computers (File Transfer Protocol)

69 TFTPHave to know what you want and where it is on the server, no directory browsing, no user authentication (Trivial File Transfer Protocol)

2049 NFS Allows remote file systems to be mounted as local (Network File System)

25 SMTP Used to send mail between mail servers (Simple Mail Transfer Protocol)

515 LPD Used for sharing of network printers with TCP/IP (Line Printer Daemon)

161 SNMPCollect and manipulates network information (Simple Network Management Protocol)

53 DNS Resolves FQDN to IP addresses (Domain Name Service)

67 BootP Used by diskless CPs to receive boot file and other info via TFTP

  DHCPAssigns IP addresses to hosts from a pool. Can send IP address, Subnet mask,Domain Name, Default Gateway, DNS IP, WINS info. (Dynamic Host Configuration Protocol)

Host to host layer protocols

Transmission Control Protocol (TCP) User Datagram Protocol (UDP)

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TCP Characteristics TCP is the acronym for Transmission Control

Protocol. TCP is

Connection oriented Reliable

It is used to carry large amounts of data. It provides services that Internet Protocol (IP)

lacks. TCP is defined in Request for Comments

(RFC) 793.

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TCP Functions

Guaranteed delivery Packet acknowledgment Flow control Error detection

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Segmentation TCP splits application layer messages into

datagram-sized segments and encapsulates each segment with its own header.

The collection of segments is called a sequence.

The destination system reassembles the segments into the original application layer messages .

The segmentation process is completely separate from the network layer fragmentation process.

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The TCP Message Format

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Control Bits

Control Bit

Function

URG Indicates that the segment contains urgent data

ACK Indicates that the message acknowledges a previously transmitted segment

PSH Indicates that the receiving system should forward the message immediately rather than wait for the rest of the sequence

RST Resets the TCP connection and discards the segments received so far

SYN Synchronizes the Sequence Number values for both systems

FIN Terminates a TCP connection

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Three-Way Handshake Functions

Verify that both computers are operating and ready to receive data

Exchange initial sequence numbers (ISNs)

Exchange maximum segment sizes (MSSs)

Exchange port numbers

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Three-Way Handshake Messages

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Transmitting Data

Information needed to transmit data: Port number Sequence number MSS (Max segment size)

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Packet Acknowledgment

TCP implements packet acknowledgment by using the Sequence Number and Acknowledgment Number fields.

The Sequence Number field specifies the number of bytes transmitted.

The Acknowledgment Number field specifies the number of bytes received.

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Delayed Acknowledgments

TCP systems do not have to individually acknowledge every packet they receive.

The frequency of acknowledgment is left up to the individual TCP implementation.

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Positive and Negative Acknowledgments

With positive acknowledgment with retransmission, TCP systems acknowledge only the number of bytes they have received correctly.

With negative acknowledgment, the computer specifies the information that it has not received correctly. All data beginning with the failed segment is

retransmitted. Messages that are not acknowledged are

retransmitted.

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TCP Error Detection

TCP provides the only end-to-end error detection for the application layer data.

TCP computes a checksum based on The TCP header The application layer information in the TCP

Data field A pseudo-header created from some of the

fields in the IP header

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TCP Checksum Value

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Flow Control Flow control allows a receiving system to control

the transmission rate of the sending system. Each computer has a buffer for storing incoming

packets. When a computer transmits too quickly, the buffer

on the receiving system can fill up, causing packets to be dropped.

TCP uses the Window field in its acknowledgment messages to implement flow control.

The Window value indicates how much buffer space the receiving system has available.

The sending system is permitted to transmit only the number of bytes specified in the Window field.

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Terminating the Connection

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UDP Characteristics

UDP is the acronym for User Datagram Protocol.

UDP is defined in RFC 768. It is a connectionless protocol. It is used primarily for brief request/reply

transactions.

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The UDP Message Format

TCP VS. UDP

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Port Numbers

In computer networking, a port is an application-specific or process-specific software construct serving as a communications endpoint used by Transport Layer protocols, such as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).

Port + IP address socket

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Well Known port numbers

< 1024 Defined in RFC 3232

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IP Layer Protocals

IP (Internet Protocol) Encapsulation Addressing Routing Fragmentation Protocol identification

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The IP Datagram Format

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ICMP

Internet Control Message Protocol Router may use ICMP to send back Destination

Unreachable message Or Buffer Full message Over hop limit message

A message informing the demise of a IP datagram ping traceroute/tracert

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ARP and RARP

Address Resolution Protocol (ARP) Resolve IP addresses to Mac addresses by

broadcast a ARP message arp -a

Reverse Address Resolution Protocol (RARP) From MAC to IP, for diskless systems

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Data Encapsulation The wrapping of protocol info at each

layer. Each layer communicate ONLY WITH ITS

PEER LAYER

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Data Encapsulation – Protocol Data Units

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Data Encapsulation

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