1 Intro to Networks (Ping, Traceroute, Wireshark)

Overview of a Network

As hardware has gotten cheaper - the distinction between an Ethernet switch (simpler device) and a Router (more complex device) has been reduced.

Yesterday we talked about Local Access Network (LAN) and Wide Area Network (WAN). When we get into IP addressing later on, we'll talk about the differences for LAN and WAN for those.

For the router interface, the interface uses a gateway. The default gateway is the router interface our PCs use to get access to the Internet. So all EE PCs on their LAN will use the EE default gateway to access the internet.

Historically they used a more hierarchical layout of having many switches, connected to a few routers.

Home Router, Modems (modulate/demodulate) and Your ISP

Modems turn your analog signal to digital, and back to analog. The signal on fiber-optic (or your wire) will be analog, and transmitted over the ISP (and then the internet). Typically when you leave your house or residence you don't have this ethernet.

Info Needed to Configure a Network

You have two things:

Ethernet is a digital signalling system, so say for example your NIC - Network Interface Card OR Wireless Adapter on your PC would connect to this ethernet and interpret the bits using the NIC. The two have to agree how the communication is done (is it two-way or one-way, for example).

Now what info do I need on a LAN to configure a PC? We need:

  1. The IP Address (ex: 192.168.3.4 is a dot-decimal format, with numbers that are 8 bits with 4 numbers = 32 bit number)
  2. The subnet mask (sometimes called the mask) (ex: 255.255.255.0) dictates the bits that change between devices on LAN.
  3. Default Gateway (ex: 192.168.0.1) is the address of the router connecting the LAN to the wider internet.
Note

How does your phone or a new device to a wifi network know these? The default gateway gives that information over the wifi network so that it then can fill in the other information for you.

We also, to maybe a lesser extent, need access to DNS servers, which translates a name to an IP address.

For instance google.com gets converted to something like 142.251.167.139. This is done via your DNS server. You can run ping google.com to try this on your own and see that IP!

Packet Flow Diagrams

These will allow us to draw information flow, and understand and design our information implementation. In project 2 we'll have to design our client (PC1) and server (PC2). One case is the client sends username/password and get's an OK from the server. Another one could be that they get a NOT OK response instead.

For a DNS server, the PC may send google.com and then get the IP address just like before.

Ethernet Frames

These are LAN protocols, and are dictates by IEEE on how to send data across that network.

For example, ethernet expects the data in a certain format, called a frame.

Here when we say address we say MAC address, since these are unique. A MAC address is of the fol lowing format:

If a vendor runs out of MAC addresses, then you can ask for another vender number. If two MAC addresses are on the same LAN then it'll create problems later when we do IP addressing.

MAC addresses are the hardware addresses of the related NIC for the device.

If PC1 on the same LAN as PC2 wants to talk to each other over the switch, they need different MAC addresses. Say MAC1 is the first and MAC2 is the second. To communicate, the PC1 requests and ethernet frame where the following is filled in: