Internet Infrastructure
                                 Backbone       ISP
                            ISP
            Local and interdomain routing
              TCP/IP for routing and messaging
              BGP for routing announcements
            DNS (Domain Name System DNS)
              Find IP address from domain name
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       TCP Protocol Stack
                             Application protocol
           Application                                        Application
                                  TCP protocol
            Transport                                          Transport
            Network      IP protocol     IP     IP protocol    Network
              Link           Dat       Network     Dat           Link
                              a        Access        a 
                            Link                   Link
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          TCP/IP Packets
                                                TCP Header
                                                                    Application message - data
                 Application           message
            Transport (TCP, UDP)       segment          TCP     data        TCP     data        TCP     data
                Network (IP)           packet                          IP   TCP     data
                 Link Layer            frame                     ETH IP     TCP     data     ETF
                                         IP Header           Link (Ethernet)             Link (Ethernet)
                                                                   Header                      Trailer
                                                                                                                4
                       Inside a LAN: 
                 Layer 2 issues - ARP
                                                     5
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       Addressing in Layer 2 / Layer 3
          Layer 3  (IP)
            IP Address
            32 bits long
          Layer 2  (MAC)
            MAC address 
            48 bits long
          How to translate from IP address to MAC 
          address?
          “Layer 2.5” protocol : ARP
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