Address Resolution Protocol
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Address Resolution Protocol



Unit 3 Of ACN

Unit 3 Of ACN



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Address Resolution Protocol Address Resolution Protocol Presentation Transcript

  • Address Resolution Protocol Presenting By:- Jatin Kumar
  • What is AR ?
    • Communication On an internetwork is done by sending data at layer three using a N/W layer address.
    • The actual transmission of data occurs at layer two using a DLL address.
    • It is necessary to define some way of being able to link these two addresses.
  • What is AR ?(Contd.)
    • This is done by taking a network layer address and determining what DLL address goes with it, this process is called address resolution.
    View slide
  • Why addressing is done at two different layers?
    • As they are very different types of addresses those are used for diff. Purposes.
    • Layer two addresses(IEEE 802 MAC addresses)are used for local transmission b/w h/w devices that can communicate directly.
    • In contrast layer three addresses(IP addresses) are used in internetworking.
    View slide
  • Why AR is necessary?
    • If a client on the local n/w is accessing a server somewhere on the internet.
    • Logically this connection can be made directly b/w the client and server.
    • But in reality is a sequence of physical links at layer two.
  • Why AR is necessary?(Contd.)
    • At each step the decision of where to send the data is made based on a layer three address.
    • But the actual transmission must be performed using layer two address.
    • Figure for CS communication.
  • Methods of Address Resolution
    • It can be accomplished in two basic ways:-
        • Direct mapping
        • Dynamic Resolution
  • Direct Mapping
    • A formula is used to map higher layer address into the lower layer address.
    • This is the simple and more efficient tech.
    • But has some limitations specially regarding the size of DLL address compare to n/w layer address.
  • 222 101 33 29 11011110 01100101 00100001 00101001 29 00101001 8 bit h/w address (#29) Decimal Binary 32 bit IP address ( Address Resolution through direct mapping
  • Address Resolution through direct mapping
    • The basic idea behind direct mapping is to choose a scheme so that we can determine one from the other using a simple algorithm.
    • When the layer two address is smaller than the layer three address is possible to define a direct mapping b/w them so that the h/w address can be determined directly from the n/w layer address.
    • This makes AR extremely simple but reduces flexibility.
  • Direct mapping is not possible with large h/w address.
    • If the layer two address is bigger than the layer three address there is no way to do direct mapping.
    • Ethernet is the most popular tech at layer two and uses a 48 bit addresses and IP is the most popular tech at layer three and uses a 32 bit address.that’why DM is not widely used.
  • 32 bit IP address (?) 0 8 16 24 32 40 4 8 ? ? ? ? ? ? ? ? Decimal Binary 0A A7 94 07 CB D0 00001010 10100111 10010100 00000111 11001011 11010000 48 bit h/w address(0A-A7-94-07-CB-D0)
  • Dynamic Address Resolution
    • Dynamic address resolution is usually implemented using a special protocol.
    • A device that knows only the n/w layer address of another device can use this protocol to request the other device’s h/w address.
  • LAN Switch Device C IP address: IPC H/W address: #46 Device A IP address: IPA H/W address: #43 Device B IP address: IPB H/W address: #79 Device D IP address: IPD H/W address: #48 Who is IPB? IPB is #79
  • Dynamic Address Resolution(Contd.)
    • In the previous device A has to send the data to device B but knows only its IP address (“IPB”),and not its H/W address. A broadcast request asking to be send to the H/W address of the device using the IP address “IPB”.B responds back to A directly with the H/W address.
  • About ARP
    • ARP is a relatively simple request/reply protocol.The source device broadcasts an ARP request looking for a particular device based on it IP address.The device responds with its h/w address in an ARP reply message.