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Chapter 19 - Binding Protocol Addresses

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Upper levels of protocol stack use protocol addresses. Network hardware must use hardware address for ... Upper layer hands down protocol address of destination ... – PowerPoint PPT presentation

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Title: Chapter 19 - Binding Protocol Addresses


1
Chapter 19 - Binding Protocol Addresses
  • Translation
  • Address Resolution
  • ARP (Address Resolution Protocol)
  • Note Sections 19.4 to 19.7, 19.13 and 19.15 will
    not be covered

2
Introduction
  • Upper levels of protocol stack use protocol
    addresses
  • Network hardware must use hardware address for
    eventual delivery
  • Protocol address must be translated into hardware
    address for delivery

3
Address translation
  • Upper levels use only protocol addresses
  • "Virtual network" addressing scheme
  • Hides hardware details
  • Translation occurs at data link layer
  • Upper layer hands down protocol address of
    destination
  • Data link layer translates into hardware address
    for use by hardware layer

4
Address resolution
  • Finding hardware address for protocol address
  • address resolution
  • Data link layer resolves protocol address to
    hardware address
  • Resolution is local to a network
  • Network component only resolves address for
    other components on same network

5
Address resolution (continued)
  • A send to B A resolves protocol address for B
    for protocol messages from an application on A
    sent to an application on B
  • A send to F A does not resolve a protocol
    address for F (F on a different network)
  • Through the internet layer, A delivers to F by
    routing through R1 and R2
  • A resolves R1s hardware address
  • R1 resolves R2s hardware address
  • R2 resolve Fs hardware address

6
Address resolution
7
ARP
  • IP uses distributed resolution technique
  • Address Resolution Protocol (ARP) - part of
    TCP/IP protocol suite
  • Two-part protocol
  • Request from source asking for hardware address
  • Reply from destination carrying hardware address

8
ARP message exchange
  • ARP request message dropped into hardware frame
    and broadcast
  • Sender inserts (Target or destination) IP address
    into message and broadcast
  • Every other computer examines request
  • Computer whose IP address is in request responds
  • Puts hardware address in response
  • Unicasts to sender
  • Original requester can then extract hardware
    address and send IP packet to destination

9
ARP example
10
ARP message contents
  • Maps protocol address to hardware address
  • Both protocol address and hardware address sizes
    are variable
  • Ethernet 6 octets
  • IP 4 octets
  • Can be used for other protocols and hardware
    types

11
ARP message format
  • HARDWARE ADDRESS TYPE 1 for Ethernet
  • PROTOCOL ADDRESS TYPE 0x0800 for IP
  • OPERATION 1 for request, 2 for response
  • Contains both target and sender mappings from
    protocol address to hardware address
  • Request sets hardware address of target to 0
  • Target can extract hardware address of sender
    (saving an ARP request)
  • Target exchanges sender/target in response
  • (Target computer reverse sender and target
    hardware address. It now uses the senders
    hardware address as target hardware address and
    send a response to the sender)

12
ARP message format
13
Sending an ARP message
  • Sender constructs ARP message
  • ARP message carried as data in hardware frame -
    encapsulation

14
Processing ARP messages
  • Receiver extracts sender's hardware address and
    updates local ARP table
  • Receiver checks operation - request or response
  • Message is a Response
  • Adds sender's address to local cache
  • Sends pending IP packet(s)
  • Message is a Request
  • If receiver is target, forms response
  • Unicasts to sender
  • Adds sender's address to local cache

15
Summary
  • Address resolution - translates protocol address
    to hardware address
  • ARP - TCP/IP protocol for address resolution
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