csci 465 d ata communications and networks lecture 24 martin van bommel csci 465 data communications...
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CSCI 465Data Communications and Networks
Lecture 24
Martin van Bommel
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Internet
• An interconnected set of networks where each of the constituent networks retains its identity and protocols
• Consists of– End systems
• devices attached to a network
– Intermediate systems• provide a communications path and perform the
necessary relaying and routing functions• bridges and routers
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Bridge vs Router
• Bridge– intermediate system to connect two LANs that use
similar LAN protocols– acts as address filter to transfer packets– operates at layer 2 - network access layer
• Router– intermediate system to connect two networks
that may or may not be similar– operates at layer 3 - internet layer
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TCP/IP Concepts
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Internetworking Requirements
• Provide a link between networks– At minimum, physical and link control is needed
• Router J has physical links to N1&N2 - data link protocol
• Provide for the routing and delivery of data• Application X on host A exchanges data with X on host B
• Provide an accounting service– Track of use and status of networks and routers
• Provide the services regardless of architectures
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Network Differences
• addressing schemes (but global IP address)• maximum packet size – break up for smaller• network access mechanisms• timeouts• error recovery• status reporting• routing techniques• user access control• Connection vs connectionless
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Connectionless Operation
• Internetworking is connectionless at IP level– Each network protocol data unit (PDU) is routed
independently through series of routers
• Advantages– Flexible – requires very little from underlying nets– Robust – responds to changing conditions– Less overhead – no connection established
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IP Operation
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IPv4 – Internet Protocol Version 4
• Part of the TCP/IP suite• Two parts– Specification of interface with higher layer• Interaction with e.g. TCP
– Specification of actual protocol format and mechanisms
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IP Services
• Service Primitives – send and deliver• Parameters
– Source and destination address– Protocol – e.g. TCP or UDP– Type of service indicators– Identification – used for reassembly– Don’t fragment identifier– Time to live (TTL) – in seconds– Data length– Option data – specify user options (next slide)– Data itself
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IP Options Parameter
• Security• Source routing– Sequence of router addresses
• Route recording– Sequence of routers visited
• Stream identification– Identify as stream to gain certain resources
• TimestampingCSCI 465
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IPv4 Header
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IPv4 address Formats
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IP Addresses – Class A
• Start with binary 0• Range 0.x.x.x to 127.x.x.x– 0 is reserved– 127 used for loopback
• 126 Class A network numbers• 224 = 16.7 million host numbers on each
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IP Addresses – Class B
• Start with binary 10• Range 128.x.x.x to 191.x.x.x– Second octet also used as part of network number
• 214 = 16,384 Class B network numbers• 216 = 65,536 host numbers on each
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IP Addresses – Class C
• Start with binary 110• Range 192.x.x.x to 223.x.x.x– Second and third octets also used as part of
network number
• 221 = 2,097,152 Class C network numbers• 28 = 256 host numbers on each
• Network numbers nearly all allocated – IPv6CSCI 465
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Subnets and Subnet Mask
• Insulate overall internet from growth of network numbers and routing complexity– allows arbitrary complexity of internetworked LANs within
organization– site looks to rest of internet like single network
• Assign single network number to all LANs – simplifies addressing and routing to the site
• Each LAN on the site assigned subnet number– host portion of IP address partitioned into subnet and host numbers
• Local routers route on basis of subnet number– Subnet mask used to convert IP address into subnet and host numbers
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IP Addresses and Subnet Masks
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Binary Representation Dot Notation
IP Address 10001101.01101101.00100101.00011001 141.109.37.25
Subnet Mask 11111111.11111111.11110000.00000000 255.255.240.0
Bitwise AND 10001101.01101101.00100000.00000000 141.109.32.0
Subnet Number 10001101.01101101.00100101 5
Host Number 00000000.00000000.00000101.00011001 5.25 = 1305
Masks Binary Representation Dot Notation
Class A Default 11111111.00000000.00000000.00000000 255.0.0.0
Class A Example 11111111.11000000.00000000.00000000 255.192.0.0
Class B Default 11111111.11111111.00000000.00000000 255.255.0.0
Class B Example 11111111.11111111.11111000.00000000 255.255.248.0
Class C Default 11111111.11111111.11111111.00000000 255.255.255.0
Class C Example 11111111.11111111.11111111.11111100 255.255.255.252