1
CSCI 233Internet Protocols
Class 2
Dave Roberts
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
2
3
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
Good Citizen Principle
When 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
4
This is an important Internet design principle.
We will see it again and again.
Important Internet Principles
1. Good Citizen Principle—when a resource is scarce, reduce your demand for it
5
6
Tonight
• Review of networking technologies• Internetworking• Protocol Layering• Internet addresses
Early Ethernet
7
• Stiff wire, hard to bend
• Vampire connectors reduce performance
• Hard to change when offices are rearranged
Modern Ethernet
8
Ethernet Frame
9
Header Payload
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 10
Internet Architecture
11
The User’s View
12
ThisLooks Like This
Protocol Layering
• Internet protocols are organized into levels, called “layers”
• Each layer deals with certain topics
• Layers make protocols easier to understand
13
Just Think of Problems
• Hardware failure• Network congestion• Packet loss• Data corruption• Data duplication• Data arriving out of sequence
14
Layering and Problems
• Layering allows a problem to be solved in just one layer
• Especially, applications do not have to deal with network problems
15
Layers
16
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
17
OSI Model
• We may have an exercise or two• The course is about Internet
protocols• You will never be examined on the
OSI model
18
TCP-IP 5-Layer Reference Model
19
VERY
IMPORTANT!!!!
Important Boundaries
20
In Reality
21
How It Works
22
What’s Happening
1. 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
23
Encapsulation
24
IP Demultiplexing
25
INTERNET ADDRESSING
26
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.
27
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
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
29
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
30
IPv6 Address Assignments
31
IPv4 to IPv6 Transition
32
IPv6 Address Split
33
Question• How many Internet addresses can one
host have?• As many as it has network adapters
34
IP Addresses
35
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
36
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
37
38
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
39
Dotted Decimal Notation
32-bit Internet address
10000000 00001010 00000010 00011110
Is written
128.10.2.30
40
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 routing
There have been other refinements—to discuss later
Class Determination Algorithm
41
Address Class Characteristics
42
Host Capacities
43
IP Address Split
44
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
45
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)
46
47
Special IP Addresses
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
48
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!!
49