Networking

1
Networking

• Material taken mainly from HowStuffWorks.com

2
The Internet

• A network of networks
• Computers
• Servers and clients
• routers
• switches

3
Ethernet Network
The original Ethernet described communication
over a single cable shared by all devices on the
network. Once a device attached to this cable, it
had the ability to communicate with any other
attached device.
Each Ethernet devices has a unique address.
The Ethernet protocol specifies a set of rules
for communication.
4
Network Interface Cards (NIC)
The computer gives the NIC a message for another
networked device and the NIC formats that message
for transport over the Ethernet. The reverse is
also true, the NIC receives messages from the
network and reformats them so that the computer
can understand.
5
Ethernet Frame
6
Switched Ethernet
A switch creates a series of instant networks
that contain only the two devices communicating
with each other at that particular moment.
Switches maintain their own Medium Access Control
(MAC) look-up tables. These table indicate which
network device is at which port on the switch.
The look-up tables are constantly updated. When a
switch is newly installed, it will construct its
table via an Address Resolution Protocol (ARP)
broadcast.
7
Local Area Network (LAN)
8
Virtual LANs

• Advantages
• Scalability
• Security

• UNCA VLANs
• Dorms
• Student, faculty, and labs
• CSCI
• ENGR and ATMS

9
Routers
Routers are devices that let messages flow
between networks

• A router uses a configuration table to determine
  where packets go. A configuration table is a
  collection of information, including
• Information on which connections lead to
  particular groups of addresses
• Priorities for connections to be used
• Rules for handling both routine and special cases
  of traffic

10
Network Addresses
Most switches operate at the Data layer (Layer 2)
of the OSI Reference Model, while routers operate
at the Network layer (Layer 3)
When a router receives a packet, it looks at the
Layer 3 source and destination addresses to
determine the path the packet should take. A
standard switch relies on the MAC addresses to
determine the source and destination of a packet,
which is Layer 2 (Data) networking.
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Open Systems Interconnection (OSI) standard
Application Set Layer 7 Application - Layer
that interacts with the operating system or
application whenever the user chooses to transfer
files, read messages or perform other
network-related activities. Layer 6
Presentation - Takes the data provided by the
Application layer and converts it into a standard
format that the other layers can understand.
Layer 5 Session - Establishes, maintains and
ends communication with the receiving device.
Transport Set Layer 4 Transport - Maintains
flow control of data and provides for error
checking and recovery of data between the
devices. Layer 3 Network - Logical routing and
addressing are handled here. Layer 2 Data
Assigns the appropriate physical address. Layer
1 Physical - This is the level of the actual
hardware.
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Why Protocol Hierarchies

• The philosopher-translator-secretary architecture.

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Protocol Layering and Data

• Each layer takes data from above
• adds header information to create new data unit
• passes new data unit to layer below

14
IP Address

• Each machine on the Internet is assigned a unique
  address called an IP address. IP stands for
  Internet protocol, and these addresses are 32-bit
  numbers, normally expressed as four "octets" in a
  "dotted decimal number."
• Example 216.27.61.137
• Every machine on the Internet has a unique IP
  address.

15
Names

• People have trouble remembering the strings of
  numbers that make up IP addresses, and because IP
  addresses sometimes need to change, all servers
  on the Internet also have human-readable names,
  called domain names.
• A set of servers called Domain Name Servers (DNS)
  maps the human-readable names to the IP
  addresses. These servers are simple databases
  that map names to IP addresses, and they are
  distributed all over the Internet.
• Example
• www.howstuffworks.com for 209.116.69.66

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Clients and Servers
Any server machine makes its services available
to the Internet using numbered ports, one for
each service that is available on the server.

• Here are some common port numbers
• echo 7
• daytime 13
• qotd 17 (Quote of the Day)
• ftp 21
• telnet 23
• smtp 25 (Simple Mail Transfer, i.e., e-mail)
• time 37
• nameserver 42
• nicname 43 (Who Is)
• gopher 70
• finger 79
• WWW 80

Logical port numbers correspond to application
layer programs.
These port numbers are included in the address
information of a packet.
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Things to try

• Type IPCONFIG at the MSDOS prompt
• Type tracert www.cs.unca.edu at the MSDOS
  prompt.
• Type arp a at the MSDOS prompt.
• Type "telnet web67.ntx.net 13" at the MSDOS
  prompt.

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WinSCP Secure FTP

• File Transfer Protocol used to transfer files
  from one machine to another
• Select start - CSCI programs - WinSCP
• Features
• Its free! (http//winscp.sourceforge.net/eng/)
• Provides a dual panel display
• Copy and move files and folders (to and from a
  remote computer).
• Rename files and folders
• Create new folders
• Change properties of files and folders
• Edit files

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WinSCP Assignment

• Logon
• User Name first 6 letters of last name followed
  by first initial and middle initial
• Password CSCI followed by last 4 digits of
  student id

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WinSCP Assignment (continued)

• Transfer your webpage to your public_html
  directory on candler and give it the name,
  index.html
• Set the file and folder properties to allow the
  world to view your file
• Select the folder or file and right-click, then
  select Properties
• Set the properties as shown on the right
• View your page in your browser using the
  following address
• www.cs.unca.edu/userName

Put your user name here