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    CS378: Computer Networks Lab: Topic 01: Overview

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    Aaizah Wani
    This document provides an overview of computer networks and networking concepts such as the TCP/IP protocol stack, networking code organization, naming and addressing conventions, packet encapsulation and forwarding, common diagnostic tools like tcpdump and Wireshark, and miscellaneous tips for a computer networks lab course. Key topics covered include the layers of the TCP/IP model, domain name resolution, IP and MAC addresses, port numbers, packet header formats, packet sniffing, and ensuring equitable participation during lab exercises.

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    CS378: Computer Networks Lab: Topic 01: Overview

    Uploaded by

    Aaizah Wani
    244 views22 pages
    This document provides an overview of computer networks and networking concepts such as the TCP/IP protocol stack, networking code organization, naming and addressing conventions, packet encapsulation and forwarding, common diagnostic tools like tcpdump and Wireshark, and miscellaneous tips for a computer networks lab course. Key topics covered include the layers of the TCP/IP model, domain name resolution, IP and MAC addresses, port numbers, packet header formats, packet sniffing, and ensuring equitable participation during lab exercises.

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    Cs378 Lab00 Overview

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    This document provides an overview of computer networks and networking concepts such as the TCP/IP protocol stack, networking code organization, naming and addressing conventions, packet encapsulation and forwarding, common diagnostic tools like tcpdump and Wireshark, and miscellaneous tips for a computer networks lab course. Key topics covered include the layers of the TCP/IP model, domain name resolution, IP and MAC addresses, port numbers, packet header formats, packet sniffing, and ensuring equitable participation during lab exercises.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    244 views22 pages

    CS378: Computer Networks Lab: Topic 01: Overview

    Uploaded by

    Aaizah Wani
    This document provides an overview of computer networks and networking concepts such as the TCP/IP protocol stack, networking code organization, naming and addressing conventions, packet encapsulation and forwarding, common diagnostic tools like tcpdump and Wireshark, and miscellaneous tips for a computer networks lab course. Key topics covered include the layers of the TCP/IP model, domain name resolution, IP and MAC addresses, port numbers, packet header formats, packet sniffing, and ensuring equitable participation during lab exercises.

    Copyright:

    © All Rights Reserved
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    Download as pdf or txt
    of 22

    CS378: 

    Computer Networks Lab

    Topic 01: Overview

    Slides borrowed from:
    Kameswari Chebrolu
    Department of CSE, IIT Bombay
    Inside Computer

      2
    Internet protocol stack
    ● Application: supporting network applications
    – FTP, SMTP, HTTP
    ● Transport: process­process data transfer application
    5
    – TCP, UDP
    transport
    ● Network: routing of datagrams from source to  4
    destination
    network
    – IP, routing protocols 3

    ● Link: data transfer between neighboring  network  link
    elements 2

    – PPP, Ethernet physical
    1
    ● Physical: bits “on the wire”

      3
    Networking Code Organization
    HTML Browser, Email Clients

    ● Most applications are 
    implemented as user space 
    processes.
    ● Protocols are implemented in 
    the system kernel
    – Socket layer
    – Protocol layer
    – Interface layer

    4
    Network Configurations Files
    ● When a host is configured to boot locally, network configuration 
    parameters are stored in files.
    ● When the system boots up, parameters are read from the files 
    and used to configure the daemons and the network interface.
    ● A parameter may be changed by editing the corresponding 
    configuration file.
    ● Examples: 
    – /etc/hosts

    – /etc/services
    – /etc/network/interfaces
    5
    Naming and Addressing
    ● Uniquely identify processes in different computers for 
    communications. www.cse.iitb.ac.in
    ● Domain name
    application application
    ● Port number
    transport transport
    ● IP address
    ● MAC address network
    Host A network
    Host A

    link link

    Asterix.iitb.ac.in
    physical physical

    6
    How to figure out the addresses of the corresponding host?
    Domain Name
    ● A user friendly name to identify a host
    ●  Domain Name System (DNS): resolves a domain name to the 
    corresponding IP address.
    ● Example:
    – www.cse.iitb.ac.in → 59.162.23.130 (outside world)

    – www.cse.iitb.ac.in →10.105.1.3 (inside IITB)
    ● A host first contacts its local DNS server to get the mapping
    – host needs to know the local DNS server address 
    (specified in configuration file)

    7
    IP Address
    ● Each interface in a host is assigned an IP address.
    ● IPv4, 32 bits, dotted­decimal notation

     IPv6, 128-bit address

    8
    Media Access Control Address
    ● Apart from IP address, each interface in a host also has a 
    hardware address (MAC address)
    ● Ethernet MAC address is 48 bits long
    – E.g 00:18:F3:96:C2:A7
    ● ARP protocol is used to translate an IP address to MAC 
    address

    9
    Port Numbers
    ● Address for the application layer user process.
    ● Port Number field specified in TCP or UDP header.
    ● Well­known port numbers
    – 1 to 255: Internet wide services
    – 256 to 1023: preserved for Unix specific services
    –  1024 and up: ephemeral port numbers
    – Port 80 is associated with http (web server)
    – Port 25 is associated with email

    10
    Encapsulation
    ● The application data is sent down
    ● Each layer adds a header to the data (PDU) from its higher layer.

    11
    Multiplexing and Demultiplexing
    ● Different higher layer protocols can use the service by the same lower 
    layer protocol.

    12
    Application Header
    ● Example: Show  Email Header

    13
    UDP Header Format

    0 16 32

    14
    TCP Header Format
    0 16 32

    15
    IP Header Format
    ● Size: 20 bytes without options.
    0 16 32

    16
    Ethernet Frame Format
     Source Ethernet (MAC) Address
     Destination Ethernet Address
     Frame Type: used to identify the payload
     CRC: used for error control

    17
    Packet Sniffer
    ● Sniffs messages being sent/received from/by your 
    computer
    ● Store and display the contents of the various protocol 
    fields in the messages
    ● Passive program
    – never sends packets itself
    – no packets addressed to it
    – receives a copy of all packets (sent/received)
    18
    Packet Sniffer Structure

    19
    Diagnostic Tools
    ● Tcpdump
    – E.g tcpdump -enx host 10.129.41.2 -w exe3.out
    ● Wireshark
    – wireshark ­r exe3.out

    http://openmaniak.com/tcpdump.php
    http://openmaniak.com/tcpdump.php

    20
    Screen Shot

    21
    Miscellaneous Stuff
    ● Time is tight: Don't loiter, get on with the task asap
    ● Discuss with partner to ensure both understand what is 
    being done
    ● Take turns (both need to learn what is happening)
    ● Each student reports “self” and “partner's” contribution to 
    the lab
    – Reality check via exam
    – Total marks weighed accordingly

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