CSCI 233 Internet Protocols Class 2
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Transcript of CSCI 233 Internet Protocols Class 2
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CSCI 233Internet Protocols
Class 2
Dave Roberts
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More on Course Mechanics
• 50 word limit on homework answers and exam answers
• “Which is better?”--trick question! Usually there is no “better”, there are tradeoffs
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Good Citizen Principle• In a crisis, when resources are
short, we tend to hoard resources• The hoarding creates shortages• What if, in a crisis, each of us
reduced our use of scarce resources?
• The Internet operates on the Good Citizen Principle
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Good Citizen PrincipleWhen a resource is scarce, instead of trying to claim as much of it as possible, reduce your use of that resource until the scarcity passes
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This is an important Internet design principle.
We will see it again and again.
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Important Internet Principles
1. Good Citizen Principle—when a resource is scarce, reduce your demand for it
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Tonight• Review of networking technologies• Internetworking• Protocol Layering• Internet addresses
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Early Ethernet
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• Stiff wire, hard to bend
• Vampire connectors reduce performance
• Hard to change when offices are rearranged
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Modern Ethernet
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Ethernet Frame
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Header Payload
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Internetworking• How to interconnect networks?
– Application level
– Network Level• Users attach to a local network• Internetworking software hides details of
networks, forwards information among them
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Internet Architecture
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The User’s View
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ThisLooks Like This
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Protocol Layering• Internet protocols are organized
into levels, called “layers”• Each layer deals with certain
topics• Layers make protocols easier to
understand
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Just Think of Problems• Hardware failure• Network congestion• Packet loss• Data corruption• Data duplication• Data arriving out of sequence
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Layering and Problems• Layering allows a problem to be
solved in just one layer• Especially, applications do not
have to deal with network problems
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Layers
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Layering Models• OSI 7-layer model
– Developed for Open System Interconnect protocol family
– International standard developed over years by ISO
– Failed• TCP/IP 5-layer model
– Developed by US DARPA for military use– Widely adopted, basis for the Internet
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OSI Model• We may have an exercise or two• The course is about Internet
protocols• You will never be examined on the
OSI model
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TCP-IP 5-Layer Reference Model
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VERY
IMPORTANT!!!!
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Important Boundaries
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In Reality
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How It Works
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What’s Happening1. Sender hands message to transport
layer, which packages message and hands it to Internet layer
2. Internet layer packages message as an IP datagram, with IP addresses, then hands it to network layer
3. Network interface puts message into an Ethernet frame, with Ethernet addresses, and sends through network adapter
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Encapsulation
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IP Demultiplexing
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INTERNET ADDRESSING
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The Internet• Is it a physical or virtual network?• It’s a virtual network, defined by
protocols that run on hosts and routers.
• Internet protocols make the Internet look like a world-wide uniform network, although it encompasses many networks that are very different from each other.
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Internet Addresses• Each host connection on the
Internet has a unique Internet address
• The addresses are designed to make forwarding of Internet packets simple
• An IP address has two parts: a prefix that identifies a network and a suffix that identifies a host on the network 28
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Need for Control• To avoid conflicts in address use, some
sort of authority is needed• It makes sense to assign addresses in
blocks, not one at a time• ICANN (Internet Corporation for
Assigned names and Numbers) oversees IP address assignment
• Originally assigned in blocks of Class A, B and C addresses
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IPv6 Addressing• Each address is 128 bits• Enough addresses for every
person on earth to have an internet with three times the addresses of the present Internet!
• 1024 addresses per square meter of the earth’s surface
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IPv6 Address Assignments
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IPv4 to IPv6 Transition
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IPv6 Address Split
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Question• How many Internet addresses can one
host have?• As many as it has network adapters
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IP Addresses
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Functions of Internet Addresses
• Provide a unique identification for a particular interface between a device and the network so that a datagram can be delivered to the correct recipient
• Enable a path to be found across the Internet to reach the recipient, a process called routing
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IP and Ethernet Addresses
• Is the IP address the same as the Ethernet address?– No!
• What is the role of each?– Ethernet: delivery on the local area
network– IP: forwarding across the Internet
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IPv4 Address• 32-bit integer, unique for each
host on the network, used in all communication with the host
• <IP address> ::= <netid> <hostid>– Netid: identifier of a network– Hostid: identifier of a host on the
network
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Dotted Decimal Notation
32-bit Internet address
10000000 00001010 00000010 00011110
Is written
128.10.2.30
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Classes of IPv4 Addresses“Classful” addresses—types A, B and C below
first 2 bits distinguish 3 primary classes
Design of these classes is for efficient routingThere have been other refinements—to discuss later
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Class Determination Algorithm
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Address Class Characteristics
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Host Capacities
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IP Address Split
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Advantages of Classful Addressing
• Simplicity and clarity—addresses and their setup are very easy to understand
• Flexibility to accommodate different sizes of networks
• Ease of separating host address for routing
• Allows for reservation of some addresses for special purposes
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Classless IPv4 Addressing
• Temporary addressing scheme that does away with class A, B, C addresses
• Network prefix can be any specified length
• Forwarding techniques expanded to account for this: called Classless Inter-Domain Routing (CIDR)
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Special IP Addresses
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IP and Ethernet Addresses
• Physical transmissions are all made using Ethernet addresses across a local area network
• IP addresses give destinations across the Internet
• When a router gets an IP datagram, it decides whether to send it on to another router or deliver it locally
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Address Resolution• If the router decides to deliver
locally, then it must find out the local network’s Ethernet address that corresponds to the IP address in the datagram
• We’ll talk about address resolution next week!!
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