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 LANsAdvantages:

•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 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

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.

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.

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)• 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 addresswww.cs.unca.edu/~userName

Put your user name here