Lecture-11 - Lecture#11 IP Addressing • Addresses are...

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Unformatted text preview: Lecture #11 IP Addressing • Addresses are designed to be hierarchical – Allows one or more levels of information to be represented in an address • Two ways of doing it: – Class-based – Class-based – Classless • Will talk about both – first introduces terminology that is still used Class-Based IP Addressing • Class A - 0nnnnnnn hhhhhhhh hhhhhhhh hhhhhhhh – First bit 0; 7 network bits; 24 host bits – Initial byte: 0 - 127 – 126 Class As exist (0 and 127 are reserved) – 16,777,214 hosts on each Class A • Class B - 10nnnnnn nnnnnnnn hhhhhhhh hhhhhhhh – First two bits 10; 14 network bits; 16 host bits – Initial byte: 128 - 191 – 16,384 Class Bs exist – 65,532 hosts on each Class B lass C 10nnnnn nnnnnnnn nnnnnnnn hhhhhhhh • Class C - 110nnnnn nnnnnnnn nnnnnnnn hhhhhhhh – First three bits 110; 21 network bits; 8 host bits – Initial byte: 192 - 223 – 2,097,152 Class Cs exist – 254 hosts on each Class C • Class D - 1110mmmm mmmmmmmm mmmmmmmm mmmmmmmm – First four bits 1110; 28 multicast address bits – Initial byte: 224 - 247 – Class Ds are multicast addresses - see RFC 1112 • Class E - 1111rrrr rrrrrrrr rrrrrrrr rrrrrrrr – First four bits 1111; 28 reserved address bits – Initial byte: 248 - 255 – Reserved for experimental use Network Masks and Routing 1. Determine class (A, B, C, D, or E—usually A, B, or C) 2. Identify network mask length (8, 16, or 24 bits) – Mask is series of 1s then series of 0s (32 bits long) – Can be represented as: • 1111111111111111111111110000 • 255.255.255.0 • /24 3. Apply mask – Result is to eliminate all but network bits 4. Make routing decision – Decision can be based on “network bits” only – Class-based addressing creates an implicit, two-level hierarchy Example • 128.111.52.10 • Class B address – So apply a 16 mask – 10000000 01101111 00000100 00001010 – 11111111 11111111 00000000 00000000 0000000 01101111 00000000 00000000 – 10000000 01101111 00000000 00000000 • 128.111.0.0 • Route on 128.111.0.0 – Until you get within 128.111.0.0 then use the rest of the bits Function of Net/Host Division 223.1.1.1 223.1.1.2 223.1.1.3 223.1.1.4 223.1.2.9 223.1.2.2 223.1.2.1 223.1.3.27 • Ability to represent an entire “subnet” with a single “prefix” • Reduces routing table size eed only keep track of 223.1.3.2 223.1.3.1 network consisting of 3 subnets LAN – need only keep track of prefixes, not every single host – The problem is that networks don’t always fit the number of hosts – Class A addresses are networks with 16M hosts 223.1.1.0/24 223.1.2.0/24 • Ability to represent an entire “subnet” with a single “prefix” • Reduces routing table size eed only keep track of Function of Net/Host Division...
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This note was uploaded on 02/19/2012 for the course ENGR 361 taught by Professor Drexel during the Spring '12 term at Bloomsburg.

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Lecture-11 - Lecture#11 IP Addressing • Addresses are...

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