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class3 - CSCI 233 Internet Protocols Class 3 David C...

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1 CSCI 233 Internet Protocols Class 3 David C. Roberts Copyright 2007, David C. Roberts, all rights reserved
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2 Topics Variations on Addressing Protocol Layering UDP
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3 Extensions of IP Addressing Original IP addressing: each host has network ID as prefix of host’s own address Classes: A 8 network ID 24 host ID B 16 network ID 16 host ID C 24 network ID 8 host ID Sites can change addressing, provided it is transparent to the rest of the Internet
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Stretching Available Addresses Proxy ARP Subnet addressing Anonymous networking 4
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5 Proxy ARP Method for one network prefix to be shared between two physical nets R has the job of maintaining the illusion of a single network. R responds to ARP requests on main network with its own physical address.
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6 Subnet Addressing Instead of network ID and host ID, IP address is treated as Internet part (network ID) and local part (previous host ID) R now routes to two subnets based on third octet of IP address. External networks deal with conventional Class B addresses.
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7 Subnet Addressing
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8 Subnet Address Assignment Subnets may grow in complex ways, not amenable to simple fixed address assignments
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9 Fixed-Length Subnetting For Class B IP Addresses
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10 Variable-Length Subnets Partition of network ID and host ID can be chosen separately for each network Once chosen, all machines on that network must honor it Can lead to address ambiguity, where one address can be interpreted differently depending on the physical network Network managers are discouraged from using variable-length subnetting
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11 Subnet Masks Site chooses 32-bit subnet mask for each network 1s specify the network part, 0s the host identifier 1111111 1111111 00000000 00000000 Specifies first two octets for network address, second two for host ID. Note that 1s and 0s do not have to be contiguous! 11111111 11111111 00001000 10000000 is a valid subnet mask!
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12 Subnet Mask Representation Subnet masks are complex to represent Usually represented in the way the local system shows binary numbers Can think of a three-tuple {<network number>,<subnet number>,<host number>} Use –1 for all 1s in the octet {128.10,-1,0}
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13 Routing with Subnets Here, H must use subnet routing in order to know whether to send a datagram to R
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This note was uploaded on 09/03/2010 for the course CS 233 taught by Professor Davidc.roberts during the Fall '10 term at GWU.

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class3 - CSCI 233 Internet Protocols Class 3 David C...

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