##Reading for Monday September 23:

1. These class notes

2. [http://en.wikipedia.org/wiki/Internet_backbone#Modern_backbone] (http://en.wikipedia.org/wiki/Internet_backbone#Modern_backbone) - Sections: Introductory paragraph, Modern backbone, and Economy of the backbone

3. http://en.wikipedia.org/wiki/Internet_Service_Provider - Entire article

4. http://www.w3schools.com/html/ - from "HTML Introduction" through "HTML Forms"

#Architecture of Internet

Backbone: Internet Service Providers (Tier 1 providers) that serve Internet Service Providers http://en.wikipedia.org/wiki/Internet_backbone#Modern_backbone

 Tier 1 networks: provide transit to providers and clients; do not buy transit

The backbone is not centralized and not hierarchical (inside the backbone)

(Other) ISP's: http://en.wikipedia.org/wiki/Internet_Service_Provider

 Tier 2 (eg, Comcast): provide transit to clients and other providers, and also buy transit

Clients (like CUNY, Lehman, or non-Internet companies)

 Tier 3 (eg, CUNY): buy transit from other providers

Local networks and hosts normally connect to tier 3 networks

In addition to connectivity, ISP's provide:

DHCP servers
DNS servers
Mail servers
Web servers
These are just extra services, for convenience -- only the routing requires ISPs
Any of the other services can be set up on any network!!!!

#Physical structure of local network

On computers: adapters and device drivers (Mac Addresses)

Wires (or wireless connection) to local router

Switches: they just forward packets

Router: cable or wireless connection to router (possibly in ISP or backbone) - linksys in room

Tier 1 and Tier 2 providers are just a collection of routers from end-user point of view

#Intro to ifconfig

ifconfig command on Unix systems

ifconfig <int> 
ifconfig <int> up/down
ifconfig <int> <ip>

Can also use System Preferences (Mac) or System Settings (Ubuntu)

#Troubleshooting

Physical connectivity: wires, lights
Data link layer: check that interfaces are UP (ifconfig, System Preferences>Network, System Settings>Network)
IP layer: need an IP address (ifconfig) on the right network
	a) from DHCP
	b) Manual if you can't get the DHCP address
A little more
	Need a default gateway: route or netstat
	Need a DNS: dig

#Class exercise

 Fix your Internet connection!

#Looking at the network Commands:

1. For IP address and some other information:

   ifconfig - Unix (using grep?)

   ipconfig - Windows How to read?

   ipconfig on Unix

Items 2) and 3) will not be on the midterm
2) For default router:

route or netstat on Linux

netstat on Mac OS X (a little irritating)

3. For connectivity information:

   ping

   arp

   traceroute

   nmap

#Looking at network packets Not on the midterm
wireshark

1. What is an Internet Service Provider?

2. What are the categories of Internet Service Provider, and how do they relate to each other? Which category is Lehman? Which category is Comcast?

3. Name three services usually provided by an Internet Service Provider.

4. Name three commands that are useful for network trouble-shooting and explain what they do.

5. What can you do when troubleshooting a computer for Internet service?