How basic networking works

CCNA Internetwork Basics

I have got my information from my CCNA book sixth Edition by Todd Lammle.

Networks and networking has grown exponentially over the last 15 years, they have evolved to light speed to keep up with huge increases in basic mission critical user needs such as sharing data and network printing.

If you have two computers connected to hub this would be a basic LAN connection, this is one collision domain and one broadcast domain. If you don't know what these terms are so doing fret, I will be going over them at a later time.

So Bob's computer wants to talk to Sally's computer, they are on the same LAN with a multi-port repeater (HUB), so how does Bob's computer talk to Sally's computer? Does Bob say, hey Sally are you there, or hey 192.168.x.x are you there? Not since it is on the same LAN it would be using the MAC addresses that are burned into the network interface card (NIC).

So how does Bob know what Sally’s mac address is if they have never communicated before? Bob will start with name resolution (hostname to IP address resolution), this is accomplished by using the Domain Naming Service (DNS). Really since they are on the same LAN, they don't need DNS; they can broadcast asking for Sally for her information. Bob can ask everybody on the subnet who has the host name sally? Sally will respond with I am over here and here is all my information. Then Bob can store that information in what is called the prefetch file. Prefetch is like a DNS for the computer, the computer will look up his own "prefetch" file and if it cannot find what it needs there then it will ask the default gateway.

Network segmentation is how we break up bigger networks into smaller ones, you do this with devices like routers, switches, and bridges. Hubs do not break up collision or broadcast domains, switches will break up collision domains but still keep one big broadcast domain. Big broadcast domains can cause network congestion, below are some common LAN traffic congestion.

1.     To many hosts in a broadcast domain

2.     Multicast

3.     Broadcast storms

4.     Low bandwidth

5.     Adding hubs for connectivity (to many hosts)

6.     Tons of ARP or IPX traffic 

Routers are used to connect network together and route packets of data from one network to another. Routers by default break up collision and broadcast domains. Routers also provide a WAN connection as well. Breaking up broadcast domains are important because when a host or server sends a network broadcast, every device within that broadcast domain has to stop what they are doing to hear the message.

When a router's interface receives a broadcast on a port, it says thanks but no thanks and drops the packet(s). Routers also break up collision domains; there are a few advantages of using routers on a network. They do not forward broadcasts; they can filter the network based on a layer 3 information (IP address), packet switching, packet filtering, internetwork communication and path selection.

We sometimes call routers layer 3 switches, unlike layer 2 switches, which forward or filter frames, routers use logical addressing and provide what is called packet switching. Routers can also provide packet filtering by using access lists, and when routers connect two or more networks together, they use logical addressing, this is called an internetwork. Routers use routing tables (map of the internetwork) to make path selections and to forward packets to remote networks. Switches do not create internetworks; they are employed to add functionality to a network LAN. The main purpose of a switch is to make the LAN work better or to optimize its performance, providing more bandwidth to the users on that subnet. Switches do not forward packets to other networks as routers do; instead they only "switch" frames from one port to another within the switched network. 

Bridging was introduced before routers and hubs were introduced, so its pretty common to hear people referring to bridges as switches. They basically do the same thing; break up collision domains on a LAN.