ipmacaddresstranslation(參考版)
2024-10-16 15:41本頁面
【正文】 IP/MAC Address Translation Outline ARP RARP DHCP CS 640 2 Transition from Network to Datalink ? How do we get datagrams to the right physical host? – Tricky part es when a router is forwarding to a LAN with multiple hosts (which is typically the case) ? IP datagrams contain an IP address – Configured in OS ? NIC’s only understand addressing of their particular work – Ether’s 48 bit MAC addresses CS 640 3 Address Translation Problem ? We need a means for mapping IP addresses into MAC (physical) addresses – Destination host – Next hop router – We can then encapsulate (surpirse!) IP datagrams inside a frame with link level address ? Possible mapping techniques – Encode physical address in host part of IP address ? Make physical address the same as the host portion of IP address ? Obviously not possible using IPv4 and Ether – Build a table of IP/MAC pairs ? How is it maintained? CS 640 4 Address Resolution Protocol (ARP) ? ARP is part of the TCP/IP specification ? Enable each host to build table of IP to physical address bindings – Dynamic binding protocol – no static entries in table – Allows new nodes to be easily added to broadcast work ? Simple idea: broadcast request if an IP address not in table – Supported by link level technology – Determine host B’s physical address PB from it IP address IB 1. Host A broadcasts an ARP request containing IB to all hosts on LAN 2. Host B responds with an ARP reply containing
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