Networking Devices

 Network devices

Hubs

A hub is networking device and serves as a central point to which all of the computers/hosts in a network connect to. It is Layer 1 device of OS model and has no concept of Ethernet framing or addressing – it simply receives the data from one port and transmit it out to all other ports...

As mentioned above picture, hubs have no way to determine out which port a signal should be sent to; rather then, an electrical signal is sent out each port. And all nodes on the network will receive data, and the data eventually reached the correct destination, but with lot of unnecessary traffic in the network:

In the above example you can see the hub has sent out the receiving signal to all other port, beside the incoming port. Hubs are considered out of date and switches are used instead in modern LANs. Hubs have several disadvantages over switches:

• they are not aware about traffic that pass through them.
• they create one large collision domain.
• a hub typically operates in half duplex mode.
• there is also a security issue with hubs since the traffic forwarded to all other ports (except the source port), which make it possible to catch all the traffic on a network with network sniffer!

NOTE
Hubs are also called multiport repeater as this is basically what they do – and repeat the electrical signal that comes in one port out all others ports (except the incoming port).

Switches

Just like hubs and bridge, a switch is used to connect multiple devices together, and it has many advantages. Switch is Layer 2 device of OSI model, which means that can be inspect receiving traffic and make forwarding decisions. Each port on switch is a seperate collision domain and can run in full duplex mode.

A switch manage the flow of data over a network by inspecting the incoming frames destination MAC addresses and forwarding the frame only the host for which the data was intended. Every switches has dynamic table (called the MAC table) and that maps the MAC addresses to ports. With the of MAC table, a switch can identify which system is located on which port and where to send the received frame.

As you can see from that above example , Host A is trying to communicate with Host C and transmit a frame with the Host C destination MAC. The frame arrives at the switch, which looks at destination MAC. The switch searches that MAC address in its MAC table. If the MAC address found, then the switch forwards the frame only out the port connected to the frame’s destination. Hosts connect to the other ports will not receive frame.

Routers

A router is a networking device that transmit packets from one network to another network. It is usually connected with different two or more networks. When a packets come to a router port, the router read the address information in the packet to decide to out which port the packet will be sent. and it is layer 3 device of the OSI model.

NOTE
A router is a network Layer device, since it is forwarding decision based on the information of the Layer 3 – the destination IP. Routers divide broadcast domain, provide full duplex mode communication, and also have traffic filtering capabilities.

If two computers from different networks want to communicate, so they will need a router in order to exchange information:

We have three computers and a router in above network. Note that every computer is on a different network. If Host A wants to communicate with Host B and sends the packet with the Host B’s IP (10.0.0.20) to the router. The router receive the packet, And compares the packet destination IP to the entries in its routing table and searches a match. It sends packet out the interface associated with network 10.0.0.0/24. Only Host B will received and process the packets. actually , Host C will not be aware that the communication took place.