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IDSC 4490 – Network Security. Networking Review (I) Alok Gupta, Dept. of IDSC. Topics. LANs Bridges Hubs and Switches Media Access Control (MAC) address IP numbering Domain Names Network Classes Subnets Routing. Local Area Networks. LAN topologies Star Ring Bus

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Idsc 4490 network security l.jpg

IDSC 4490 – Network Security

Networking Review (I)

Alok Gupta, Dept. of IDSC


Topics l.jpg
Topics

  • LANs

  • Bridges

  • Hubs and Switches

  • Media Access Control (MAC) address

  • IP numbering

  • Domain Names

  • Network Classes

  • Subnets

  • Routing


Local area networks l.jpg
Local Area Networks

  • LAN topologies

    • Star

    • Ring

    • Bus

  • Most Used

    • Star

    • Ethernet

  • All computers on a LAN can receive all the transmitted packets


Bridges l.jpg
Bridges

  • Why Bridges?

    • LANs have limitations in terms of the length of ether and the number of computers

    • Bridges connect different segments of a LAN

    • Data is sent to the other segment only if the receiving computer is on the other segment


Slide5 l.jpg
Hubs

  • Look like Star act like Bus

  • Sometimes called ``Ethernet-in-a-box''

  • Effectively a very short Ethernet with very long cables

  • Can be connected into larger Ethernets


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Bridge

  • With switching, multiple stations can transmit simultaneously

  • Provides much higher aggregate bandwidth

Switches

  • Effectively a separate LAN segment for each port

  • Similar to hub - hub shares single segment among all ports


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NICs and MACs

  • Computer systems use special purpose hardware for network connection

    • Typically a separate card in the back panel

    • Network adapter card or network interface card (NIC)

  • Each card usually has a unique hardware number often referred to as Media Access Control (MAC) address

  • Computers on a LAN send the message to each other using MAC addresses

  • Each MAC address is unique


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Internet -- Glossary

  • An internet is a collection of physical networks interconnected into a single virtual network

  • Routers provide the physical interconnection and forward packets between networks

  • Hosts communicate across multiple network through packets forwarded by routers

  • TCP/IP is the most widely used internetworking protocol suite


Ip address l.jpg
IP Address

  • IP numbers are the addressing scheme in TCP/IP protocol suite

    • Each host is assigned a 32-bit number

    • This number is called the IP address or Internet address

    • This number is unique across the entire Internet


Ip address characteristics l.jpg
IP Address -- Characteristics

  • Each IP address is divided into a prefix and a suffix

    • Prefix identifies network to which computer is attached

    • Suffix identifies computer within that network

  • Address format makes routing efficient


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Domain Names

  • For ease of human reference, Domain Names can be assigned to each network/computer

  • Domain names are mapped to IP numbers for actual routing

  • The translation of domain names to IP number is done by Domain Name Service (DNS)

  • Domains can be defined in a hierarchical manner, for example

    • .edu

      • umn.edu

        • csom.umn.edu

          • Ids.csom.umn.edu


Ip address examples l.jpg
IP Address -- Examples

  • Domain umn.edu

    • 160.94.0.0 – 160.94.255.255

      • 160.94.254.1  www1.umn.edu

  • 131.212.0.0 – 131.212.255.255

    • 131.212.109.39  www.d.umn.edu

  • 146.57.0.0 – 146.57.255.255

    • 146.57.6.12  www.mrs.umn.edu

  • Domain csom.umn.edu

    • 160.94.112.0 – 160.94.119.255

      • 160.94.113.243  ids.csom.umn.edu

        *In red are network prefix – the rest are either subnet prefixes or IP numbers assigned to computers


  • Ip address binary representation l.jpg
    IP Address – Binary Representation

    128

    64

    32

    16

    8

    4

    1

    128

    64

    32

    16

    8

    4

    1

    128

    64

    32

    16

    8

    4

    1

    2

    2

    2

    128

    64

    32

    16

    8

    4

    1

    2

    1

    1

    0

    0

    1

    0

    0

    1

    0

    1

    0

    1

    0

    0

    0

    1

    1

    1

    0

    1

    1

    1

    1

    0

    0

    0

    0

    1

    1

    1

    0

    1


    Global design of ip numbers l.jpg
    Global Design of IP Numbers

    • There are a total of 32-bits

    • We can allocate some bits for prefix (network number) and some for suffix (host numbers)

      • Large prefix, small suffix—many networks, few hosts per network

      • Small prefix, large suffix—few networks, many hosts per network

    • Because of variety of usages, organizational sizes, we need to allow for both large and small networks


    Classes of ip numbers l.jpg
    Classes of IP Numbers

    • Class of an address is identified by first four bits


    Usage of ip classes l.jpg
    Usage of IP Classes

    • Class A, B and C are primary classes

    • Used for ordinary host addressing

    • Class D is used for multicast, a limited form of broadcast

      • Internet hosts join a multicast group

      • Packets are delivered to all members of group

      • Routers manage delivery of single packet from source to all members of multicast group

      • Used for mbone (multicast backbone)

    • Class E is reserved


    Recognizing a network s class l.jpg
    Recognizing a Network’s Class

    • While dotted decimal makes separating network address from host address easier, determining class is not so obvious

    • Look at first dotted decimal number, and use this table:


    Number of networks hosts l.jpg
    Number of Networks & Hosts

    • Example for Class A:

      • First bit must be 0

      • 7 remaining bits identify Class A net

      • 27 (= 128) possible class A nets


    Dividing a network l.jpg
    Dividing A Network

    • It is not always efficient to use the whole IP block assigned to an organization from a central place. For example

      • UMN has many different units that need to manage their own networks, e.g., CSOM

        • This is done by assigning a block of IP numbers to CSOM

        • The way to identify this block is by a network number and a subnet mask

        • A subnet mask is also a 32-bit number with a continuous series of 1’s up to a point, for example

          Or 255.255.248.0

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    0

    0

    0

    0

    0

    0

    0

    0

    0

    0

    0


    Identifying a network l.jpg
    Identifying a Network

    • Every network in a TCP/IP internet is assigned a unique network number

      • Usually yyy.yyy.yyy.0 or yyy.yyy.yyy.1

    • Each host on a specific network is assigned a host number or host address that is unique within that network

    • Host's IP address is the combination of the network number (prefix) and host address (suffix)


    Identifying a network number from a host number l.jpg
    Identifying a Network Number from a Host Number

    • By performing an AND operation at individual bit level using a Host’s IP Number and the Subnet Mask associated with that IP number.

      • For example www.csom.umn.edu has an IP number of 160.94.119.32 and the Subnet Mask associated with it is 255.255.248.0

    Bit Value

    128

    64

    32

    16

    8

    4

    1

    128

    64

    32

    16

    8

    4

    1

    128

    64

    32

    16

    8

    4

    1

    2

    2

    2

    128

    64

    32

    16

    8

    4

    1

    2

    IP Number

    1

    0

    1

    0

    0

    0

    0

    0

    1

    0

    1

    1

    1

    0

    0

    1

    1

    1

    0

    1

    1

    0

    1

    1

    0

    0

    1

    0

    0

    0

    0

    0

    Subnet Mask

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    1

    0

    0

    1

    1

    0

    0

    0

    0

    0

    0

    0

    0

    0

    Network Number

    1

    0

    1

    0

    0

    0

    0

    0

    1

    0

    1

    1

    1

    0

    0

    1

    1

    1

    0

    0

    0

    0

    1

    0

    0

    0

    0

    0

    0

    0

    0

    0

    In Decimal Notation: 160.94.112.0


    Ip address and mac address l.jpg
    IP Address and MAC Address

    • A computer’s IP number can change over time, however, its MAC address remains the same.

    • To actually send (route) packets to a given computer, IP numbers have to be mapped to a particular MAC address.


    Router l.jpg
    Router

    • A router is a computer with multiple IP addresses so that it can be part of multiple networks

    • If a router is connected to different types of networks (ethernet and token ring, for example) it must have multiple NICs



    Routing concept l.jpg
    Routing -- Concept

    • For efficiency, information about forwarding is stored in a routing table

      • Initialized at system initialization

      • Must be updated as network topology changes

    • Contains list of destination networks and next hop for each destination


    Routing practice l.jpg
    Routing – Practice

    • In practice, additional information is kept in routing table

    • Destination stored as network address

    • Next hop stored as IP address of router

    • Address mask defines how many bits of address are in prefix

      • Prefix defines how much of address used to identify network

      • E.g., class A mask is 255.0.0.0

      • Used for subnetting


    Routing example l.jpg
    Routing -- Example

    A packet with destination 192.4.10.76 and a subnet mask of 255.255.255.0 arrives => it’s destination is 192.4.10.0


    Next class l.jpg
    Next Class

    • How do we know whether its an email packet, Http packet, telnet packet, …?

    • What happens if a router goes down or doesn’t receive the send packets?

    • How do we know when to change routing tables?

    • Can we detect busy spots on the network?

    • How does a router find a computer when that computer moves its location?


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