Hello Operator. Mac OS
Hello Operator?
On arrival back to the office I erased the disk and reloaded the operating system from the recovery partition and proceed to set it back up again. 20 mins later I was done and back working, I then proceeded to setup and install all the applications that I required, such as office 2016, antivirus, our Two-Factor Authentication product and various other bits and pieces which to be fair was. So here we'll make a command line operating system. As we saw the previous code, the code just writes some text on screen via Console.WriteLine function. Now we will write a OS where the user gives the input and the computer processes it. So, lets make a code which prints Hello User!
Before we jump into the switches we use in our day to day lives at the office. I would like to take you back again to a time when we had telephone operators who would “switch” our calls for us. These operators had the job of picking up any calls that would come in. You would tell them who you are trying to reach and they would connect your line by physically moving a cable from one port on the switchboard to the port of the person you are calling. Their phone will ring and now you are able to have a telephone conversation.
I want you to remember the concept of the operator having to take a physical wire and connect it to a different port as we will be making our own switches do this for us in a similar fashion automatically for us as we start discussing the network switch next.
The Network Switch
Now what is a switch and what does it do? Similar to the call operators it is a central point where cabling goes into (physical) in order to receive frames or “Signals” that are then switched out of the correct ports, switches are an evolution of networking technology which is a great advancement from things such as hubs as well as bridges, the switch is smart enough to switch traffic specifically on a port basis where only the port where the recipient is connected to will receive the frames and the sender will receive any return traffic back, things such as hubs would broadcast the traffic out of all the ports causing problems such as increased network traffic as well as major security concerns as everyone would receive your data.
The process a switch follows is quite straight forward and I will quickly list the details here while we reference the OSI Model as well.
1) The switch will receive a frame on one of its ports and this frame will contain a destination and source MAC-address.
2)The switch will put an entry in its CAM Table or MAC-Address table of which port the frame came from and it will do a lookup against the MAC-Address table if the destination MAC-Address has been learned.
3)If the destination MAC-Address has not yet been learned the switch will send a broadcast message out (an ARP) of all of its ports to try and learn the MAC-Adress.
4)If the destination MAC-Address has been learned the frame will be sent out of the port where the MAC-Address has been learned if no MAC-Address is learned the frame will be dropped.
That is the base function the switch has, it is there to learn MAC-Addresses and switch the traffic in and out of ports, we also have additional features to talk about such as VLANs where the switch can partition some of its ports into different broadcast domains, meaning if the switch receives a frame with a VLAN tag added to the header it will only forward the frame out ports that also have this same VLAN tag configured to it.
Media Access Control Address
A Media Access Control Address or for short a MAC-ADDRESS. This is a physical 48bit address that is burned into each and every NIC when manufactured. These addresses will contain information on the OUI (Organizational Unique Identifier) as well as NIC specific information, think of the OUI as the vendor where Cisco, Juniper or Mikrotik devices will have their own unique 24bit address added to the front of each MAC-Address which serves as proof that this hardware belongs to this vendor.
Think of the MAC-ADDRESS as the IP address that switches use to communicate and that switches transfer frames by sending them out of a port for a specific MAC-ADDRESS, this is all pure Layer 2 communication.
Virtual Local-Area-Network (VLANs)
Hello Operator. Mac Os Catalina
If you’re new to networking then the idea of VLANs might confuse you a little however, I will do my best to explain what a VLAN is in the easiest terms possible. VLANs allow us a way to assign our switch ports into different broadcast domains. VLANs also follow a standard called 802.1Q. If you recall I mentioned that a switch will send a broadcast message whenever it is doing a lookup for a MAC-ADDRESS. When we start adding VLANs to the Layer 2 equation the lookup will only be done on the broadcast domain that the frame was received so if you have a Laptop in VLAN1 trying to send a frame, the switch will receive the frame and only send the frame out of ports that also have VLAN1 assigned to it, the machines in VLAN2 will not receive any broadcast messages and no frames will be passed between machines in different VLANs.
This is useful for segmenting your network and could potentially also be a security requirement for the company you work for, where machines in your finance department may only see other finance department machines. Another use for this would be to split up customer networks as well, you could potentially use the same switch for many different customers and none of their frames will be exchanged with each-other due to how VLANs function.
Conclusion
You have now learned how switches work in our day to day lives and how layer 2 frames are passed between ports as well as what a Mac-Address is and what VLANs are, this is a very important fundamental for any network engineer as this plays a big part in your daily work, the bigger the networks you support the more VLANs you will start seeing and the more switches you will be supporting. I hope this has been informational for you and that you have learned something new.
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Hungry for more?
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Why not check out the follow-up post on routers and routing
https://thenetworkberg.com/routers-and-routing to get more insight on how routing works or check out the previous article for a refresher on host-to-host communication on what a network is
https://thenetworkberg.com/networking-basics