Lecture 4

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Unformatted text preview: t is its IP address? What’s the IP address of its router? Etc. –  At least Ethernet address is on NIC Hey, where am I? 45 Gexng IP Addresses (2) 1.  Manual configura8on (old days) –  Can’t be factory set, depends on use 2.  A protocol for automa8cally configuring addresses (DHCP) –  Shils burden from users to IT folk What’s my IP? Use A.B.C.D 46 23 10/23/13 DHCP •  DHCP (Dynamic Host Configura8on Protocol), from 1993, widely used •  It leases IP address to nodes •  Provides other parameters too –  Network prefix –  Address of local router –  DNS server, 8me server, etc. 47 DHCP Protocol Stack •  DHCP is a client- server applica8on –  Uses UDP ports 67, 68 DHCP UDP IP Ethernet 48 24 10/23/13 DHCP Addressing •  Bootstrap issue: –  How does node send a message to DHCP server before it is configured? •  Answer: –  Node sends broadcast messages that delivered to all nodes on the network –  Broadcast address is all 1s –  IP (32 bit): –  Ethernet (48 bit): ff:ff:ff:ff:ff:ff 49 DHCP Messages Client Server One link 50 25 10/23/13 DHCP Messages (2) Client Server DISCOVER Broadcast OFFER REQUEST ACK 51 DHCP Messages (3) •  To renew an exis8ng lease, an abbreviated sequence is used: –  REQUEST, followed by ACK •  Protocol also supports replicated servers for reliability 52 26 10/23/13 Sending an IP Packet •  Problem: –  A node needs Link layer addresses to send a frame over the local link –  How does it get the des8na8on link address from a des8na8on IP address? M...
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This document was uploaded on 04/04/2014.

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