ETHERNET HUB
Hello everyone, today we are going to talk about common network devices. The first device we’re going to talk about is the Ethernet Hub. This is a physical layer device that acts as a multiport repeater. What does that mean you ask? It means that when a signal is transmitted out of one port, the ethernet hub repeats that signal out to every single device connected to a port on that hub. So say an ethernet hub has 10 ports, and PCs are connected to all 10. If PC1 on port 1 sends bits to PC2 on port 2 every other PC on the other 8 ports receives that message even if it wasn’t meant for them. The ethernet hub is not the smartest device and cannot do any unicast message of any kind. This device is a Layer 1 device and obsolete in our day in age.
ETHERNET SWITCH
The second network device we’re going to talk about is the device that has made the ethernet hub obsolete. We are going to talk about an ethernet switch. An ethernet switch operates at Layer 2 of the OSI model and it is known for its intelligent switching and forwarding of ethernet frames directly to a known host without the unnecessary broadcasting. Switches forward frames intelligently because they use MAC addresses to identify which host belongs to which port. This device can forward both unicast and flooding, but they are used strategically. If a switch doesn’t know the MAC address of a specific host plugged into a port, the switch floods an unknown unicast frame out of all the ports except the port it came from until the right receiver responds back. When the MAC address is learned it no longer floods frames, it records the MAC address of the host along with the port in a table called a MAC address table or CAM table. Whenever traffic is destined for that specific MAC, it does a lookup on the CAM table to intelligently forward the frame ONLY to the destination port, reducing unnecessary broadcast traffic.
ROUTER
The next device we are going to talk about is a Router. The router operates at layer 3 and is responsible for internetworking. A router contains a routing table, which is kind of like a map that tells the router where to forward a packet and how to get there. The router relies on this routing table to actually know what to do, without it there would be no web browsing or talking to your friend a couple states away. The routing table consists of routes which are essentially rules on how to get to a remote network. It includes destination network, subnet mask, next hop address, or an outgoing interface. When the router receives a packet for a subnet that is not connected or local, it must search the table to find out if there is a route for it and if there is a route, then it follows the instructions and forwards it to the next hop.
FIREWALL
Next up is the firewall. A firewall is essential for networks from a security perspective. The firewall is responsible for controlling incoming and outgoing traffic from a network based on ports, protocols or IP addresses. They are usually configured individually to explicitly deny or allow traffic coming in and out of the network. It establishes a barrier between a trusted internal network and an untrusted external network. It comes in different forms, it can either be a software on a host such as a computer, or a dedicated device.
LAYER 3 SWITCH
There is also a Layer 3 switch. This is a switch that has the ability to operate at both the layer 2 and 3. It can perform high speed switching with MAC addresses but it can also forward packets based on IP addresses. This switch is versatile and can also perform Inter-VLAN routing at faster speeds than routing because of a hardware based function called ASICs(Application-Specific Integrated Circuits). The ports can switch from being either a routed port or it can just function as a normal switchport. Although they can perform Inter-VLAN routing faster than traditional software-based routers, they typically lack WAN networking and routing.
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