255255255 ethernet 48 bit 49 dhcp messages client

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Unformatted text preview: s B, 216 addresses 10 110 Class C, 28 addresses Network por8on Host por8on 37 IP Forwarding •  All addresses on one network belong to the same prefix •  Node uses a table that lists the next hop for prefixes Prefix 192.24.0.0/19 Next Hop D 192.24.12.0/22 B A B D C 38 19 10/23/13 Longest Matching Prefix •  Prefixes in the table might overlap! –  Combines hierarchy with flexibility •  Longest matching prefix forwarding rule: –  For each packet, find the longest prefix that contains the des8na8on address, i.e., the most specific entry –  Forward the packet to the next hop router for that prefix 39 Longest Matching Prefix (2) 192.24.63.255 Prefix 192.24.0.0/19 Next Hop D 192.24.12.0/22 B /19 192.24.15.255 More specific /22 192.24.12.0 192.24.6.0 à༎ 192.24.16.32 à༎ 192.24.0.0 IP address 40 20 10/23/13 Flexibility of Longest Matching Prefix •  Can provide default behavior, with less specifics –  To send traffic going outside an organiza8on to a border router •  Can special case behavior, with more specifics –  For performance, economics, security, … 41 Performance of Longest Matching Prefix •  Uses hierarchy for a compact table –  Relies on use of large prefixes •  Lookup more complex than table –  Used to be a concern for fast routers –  Not an issue in prac8ce these days 42 21 10/23/13 Introduc8on to Computer Networks Helping IP with ARP, DHCP (§5.6.4) Computer Science & Engineering Topic •  Filling in the gaps we need to make for IP forwarding work in prac8ce –  Gexng IP addresses (DHCP) » –  Mapping IP to link addresses (ARP) » What’s my IP? What link layer address do I use? 44 22 10/23/13 Gexng IP Addresses •  Problem: –  A node wakes up for the first 8me … –  Wha...
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This document was uploaded on 04/04/2014.

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