Networks are noisy, really noisy places and we us Vlans to limit the noise. The end device you connect too any network talks allot, think of them as being really sociable! But like the local gossip in the office everyone knows how distracting that can be. Imagine your at a concert with lots of others (this is the network your connected too) you know your friend Mandy that you want to find is somewhere in the room and you want to send Mandy a message, has she got any Cola? So the first thing you would do is to shout very loud, maybe using the performers microphone, where is Mandy? (this process is called Arp) In networking this is called a broadcast and broadcasts are limited to the network they are connected too, similar to a concert hall where you cant her the music outside, in a network you cant hear broadcasts outside of the network ( well under certain circumstances you can but we will cover this later). Assuming Mandy can hear you, she might reply ‘i am in section A row 22 seat 7’, in networking this process is called ARP where MANDY (the ip address) is mapped to Section A row 22 seat 7 (which is the mac address). Now we know where Mandy is siting, we can send her a message using the Seat number as Mandy is constantly listening for any messages that are for her.    But now in the concert, the person next to you, and the person next to them are all trying to send messages to their friends who like you don't know where they are and they want to speak now, they wont wait! In fact everyone in the concert hall is now shouting for their friends. In our concert there might be 100’s or thousands of microphones and everyone is competing for microphone time, everyone is listening for messages destined for them.    This is what a large flat network looks like and sounds like if you are a computer. To make things easier we break a logical chunk of devices into what we call subnets or Vlans.   So in our example above, you might break each row into a separate Vlan, to do this you will have one person in each row (lets call them the talker who is able to talk to other talkers in other rows as well as to everyone in their row). Now when I want to know where Mandy is, first I shout as above but this time my voice dosent carry outside of the row I am in, The Talker listens and if Mandy doesn't answer from within our row, the Talker goes out and repeats the ‘Where is mandy’ to the rest of the concert hall. Only the other Talkers hear the request and so the broadcast is limited to a smaller number of devices. The Talker in Mandys row says ‘I know where she is!!’ And so the message I send is now sent to Mandy via my talker and her talker. Now when next exchanging messages both Mandy and I know which Talker we need to use to exchange messages, but also our conversation is not overheard outside of the Rows we both sit in.    That is why we create Vlans, to cut out the distractions of noisy messages, to segment the search into logical chunks and to ensure that when we do speak, everyone doesn't have to hear our voice listening in case we say something that includes them ... View more