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1.4 networks

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

  1. when you get the address, write it down
  2. open a browser
  3. go to physics.hpa.edu
  4. now go to the numbers you wrote down.
  5. 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: 72g7j5j8