2412022 b 19 1922415255 more specic 22 19224120

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Unformatted text preview: ., TCP segment) 30 15 10/23/13 IPv4 (3) •  Some fields to handle packet size differences (later) –  Iden8fica8on, Fragment offset, Fragment control bits Payload (e.g., TCP segment) 31 IPv4 (4) •  Other fields to meet other needs (later, later) –  Differen8ated Services, Time to live (TTL) Later, with QOS Later, with ICMP Payload (e.g., TCP segment) 32 16 10/23/13 Introduc8on to Computer Networks IP Forwarding (§5.6.1- 5.6.2) Computer Science & Engineering IP Addresses •  IPv4 uses 32- bit addresses –  Later we’ll see IPv6, which uses 128- bit addresses •  Wrigen in “doged quad” nota8on –  Four 8- bit numbers separated by dots 8 bits 8 bits 8 bits 8 bits aaaaaaaabbbbbbbbccccccccdddddddd 00010010000111110000000000000001 ↔ A.B.C.D ↔ 34 17 10/23/13 IP Prefixes •  Addresses are allocated in blocks called prefixes –  Addresses in an L- bit prefix have the same top L bits –  There are 232- L addresses aligned on 232- L boundary 35 IP Prefixes (2) •  Wrigen in “address/length” nota8on –  Address is lowest address in the prefix, length is prefix bits –  E.g., 128.13.0.0/16 is 128.13.0.0 to 128.13.255.255 –  So a /24 (“slash 24”) is 256 addresses, and a /32 is one address 000100100001111100000000xxxxxxxx ↔ ↔ 128.13.0.0/16 36 18 10/23/13 Classful IP Addressing •  Originally, IP addresses came in fixed size blocks with the class/size encoded in the high- order bits –  They s8ll do, but the classes are now ignored 0 8 16 24 1 32 bits Class A, 224 addresses Clas...
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