Transcript Ethernet Packet

Networking
Material taken mainly from HowStuffWorks.com
The Internet
A network of networks
•Computers
•Servers and clients
•routers
•switches
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.
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.
Ethernet Frame
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.
Local Area Network (LAN)
Virtual LANs
Advantages:
•Scalability
•Security
UNCA VLANs:
•Dorms
•Student, faculty, and labs
•CSCI
•ENGR and ATMS
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
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.
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.
Why Protocol Hierarchies
The philosopher-translator-secretary architecture.
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
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.
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 humanreadable 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
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.
Logical port numbers
correspond to
application layer
programs.
These port numbers
are included in the
address information
of a packet.
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
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.
WinSCP Secure FTP
• File Transfer Protocol – used to transfer files from
one machine to another
• Select start -> CSCI programs -> WinSCP
• Features
– It’s 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
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
WinSCP Assignment (continued)
• Create a directory named public_html in
your CS home directory.
– Select your CS directory window (the right
pane of the WinSCP window); assure that the
title bar of that window is blue.
– Use the Create Directory button at the bottom
of the WinSCP window to create a directory
named public_html
WinSCP Assignment (continued)
• Open your public_html directory
by double-clicking on it.
• 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 rightclick, 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