Download Class 24 - Nov. 20

CSCI 465
Data Communications and Networks
Lecture 24
Martin van Bommel
CSCI 465
Data Communications & Networks
1
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
CSCI 465
Data Communications & Networks
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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
CSCI 465
Data Communications & Networks
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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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Data Communications & Networks
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Network Differences
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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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Data Communications & Networks
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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
CSCI 465
Data Communications & Networks
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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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Data Communications & Networks
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IP Services
• Service Primitives – send and deliver
• Parameters
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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
• Timestamping
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Data Communications & Networks
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IPv4 Header
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Data Communications & Networks
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IPv4 address Formats
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Data Communications & Networks
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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
CSCI 465
Data Communications & Networks
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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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Data Communications & Networks
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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 – IPv6
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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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Data Communications & Networks
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IP Addresses and Subnet Masks
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
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