Address Resolution Protocol


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Unit 3 Of ACN

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Address Resolution Protocol

  1. 1. Address Resolution Protocol Presenting By:- Jatin Kumar
  2. 2. What is AR ? <ul><li>Communication On an internetwork is done by sending data at layer three using a N/W layer address. </li></ul><ul><li>The actual transmission of data occurs at layer two using a DLL address. </li></ul><ul><li>It is necessary to define some way of being able to link these two addresses. </li></ul>
  3. 3. What is AR ?(Contd.) <ul><li>This is done by taking a network layer address and determining what DLL address goes with it, this process is called address resolution. </li></ul>
  4. 4. Why addressing is done at two different layers? <ul><li>As they are very different types of addresses those are used for diff. Purposes. </li></ul><ul><li>Layer two addresses(IEEE 802 MAC addresses)are used for local transmission b/w h/w devices that can communicate directly. </li></ul><ul><li>In contrast layer three addresses(IP addresses) are used in internetworking. </li></ul>
  5. 5. Why AR is necessary? <ul><li>If a client on the local n/w is accessing a server somewhere on the internet. </li></ul><ul><li>Logically this connection can be made directly b/w the client and server. </li></ul><ul><li>But in reality is a sequence of physical links at layer two. </li></ul>
  6. 6. Why AR is necessary?(Contd.) <ul><li>At each step the decision of where to send the data is made based on a layer three address. </li></ul><ul><li>But the actual transmission must be performed using layer two address. </li></ul><ul><li>Figure for CS communication. </li></ul>
  7. 8. Methods of Address Resolution <ul><li>It can be accomplished in two basic ways:- </li></ul><ul><ul><ul><li>Direct mapping </li></ul></ul></ul><ul><ul><ul><li>Dynamic Resolution </li></ul></ul></ul>
  8. 9. Direct Mapping <ul><li>A formula is used to map higher layer address into the lower layer address. </li></ul><ul><li>This is the simple and more efficient tech. </li></ul><ul><li>But has some limitations specially regarding the size of DLL address compare to n/w layer address. </li></ul>
  9. 10. 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
  10. 11. Address Resolution through direct mapping <ul><li>The basic idea behind direct mapping is to choose a scheme so that we can determine one from the other using a simple algorithm. </li></ul><ul><li>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. </li></ul><ul><li>This makes AR extremely simple but reduces flexibility. </li></ul>
  11. 12. Direct mapping is not possible with large h/w address. <ul><li>If the layer two address is bigger than the layer three address there is no way to do direct mapping. </li></ul><ul><li>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. </li></ul>
  12. 13. 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)
  13. 14. Dynamic Address Resolution <ul><li>Dynamic address resolution is usually implemented using a special protocol. </li></ul><ul><li>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. </li></ul>
  14. 15. 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
  15. 16. Dynamic Address Resolution(Contd.) <ul><li>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. </li></ul>
  16. 17. About ARP <ul><li>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. </li></ul>