Module 3: internet

Module 3: Internet
Your computer needs 4 things to be able to get onto the internet:
IP address, example 10.14.8.4
Subnet mask, example 255.255.0.0
Gateway/router, example 10.14.0.1
Domain name server (DNS), example 10.9.250.13
Here's what each one does:
IP address:
All traffic on the internet or local area network (LAN) is in the form of packets of information, like mail envelopes with a letter inside. Each letter you mail has two important things: the address you want it to go to, and the message inside the envelope.
TCP/IP is the format of these, which stands for Transmission control protocol and internet protocol.
The TCP part is the message, and the IP part is the envelope, with an IP address on it.
Check the IP address of your machine:
From the GUI: open system preferences, network
From the terminal: type ifconfig
Subnet mask:
Imagine you want to stay in one of two large 254 room hotels. One has long hallways, and very few floors, the other has many floors, but short hallways.
If you want to sleep, you don't want many people walking down the hall in front of your room. You want many floors with fewer rooms per floors.
This is what subnet masking does on a network. Each of the four segments can hold 254 addresses.
At home, you probably have a network that looks like this:
IP: 192.168.1.49
mask: 255.255.255.0
router: 192.168.1.1
dns: 192.168.1.1
This means that the last zero can hold up to 254 addresses (from 192.168.1.1 to 192.168.1.254)
HPA has this sort of mask:
255.255.0.0
which means that
10.14.0.0
is the elab, which can have 254 x 254 addresses
It makes for a quieter network, also providing some security as others cannot see you easily.
Router/gateway:
This is the gateway for all of your traffic, usually the access point at your home. The technical difference between these words is that a router routes traffic between two networks of the same type (like ethernet), while a gateway is between different types of networks (like a cable modem or DSL gateway)
Domain name server:
This is the computer on your network or outside that translates names into numbers, like a digital phone book.
Try this in terminal:
nslookup physics.hpa.edu
when you get the address, write it down
open a browser
go to physics.hpa.edu
now go to the numbers you wrote down.
Try this with another name, either on campus or off
Ping and traceroute:
Imagine you want to find out if a machine is responding (you can block this by using "stealth mode")
In terminal ping one of the IP addresses in your class
ping an address out on the internet
what is the difference?
now try this:
traceroute www.apple.com
It should give you a trace of the path your connection took.
Try this with other addresses on and off campus.
NSLOOKUP:
Say you want to find out the name of something, or the IP address from the name.
try this:
nslookup
(you will get a funny > sign)
type:
server 10.9.250.13
type:
physics.hpa.edu
what do you get?
where is this machine?
Try again using 8.8.8.8 as the server
The best use of this is to find out what OTHER people might call a machine.
We have several DNS servers at the elab, the main one is at 10.14.1.5
Others to try:
4.4.4.4
8.8.8.8
10.14.1.2
you can get out by typing
exit
or control-z (halt)
Migrated from Apple Server Wiki. Original page ID: a88675h826