TOPIC B02-Network Devices

 Introduction to Network Devices:

Repeater

  • Regenerate the signal over the same network before the network becomes too weak or corrupted.
  • They do not amplify the signal.
  • It is a 2 port device.
Hub
  • A multiport repeater.
  • They cannot filter data and so data packets are sent to all connected devices.
  • Collision domain of all hosts connected through same hub remains one.
Switches
  • A multiport bridge.
  • It is a data link layer device.
  • It divides the collision domain of hosts but broadcast domain remains one.
Router
  • It routes data packets based on their IP address.
  • It is a Network Layer device.
  • It divides broadcast domain of host connected through it.
Repeater
  • A repeater receives bit signals generated by NICs and other devices, strengthens them, and then “repeats” them to other parts of the network.
  • A repeater enables you to connect computers whose distance from one another would make communication impossible.
  •  A traditional repeater has two ports or connections that you can use to extend your network.
  • A multiport repeater regenerates the signals full strength.
Amount of data that can be transferred in an interval is called network bandwidth.

Hub shares bandwidth with all other connected computers.

Network Switches 
• Looks just like a hub 
• But a switch actually reads data in the message, determines which port the destination device is connected to, and forward the message to only that port.

Network Switches
 • Basic Switch Operation
 • Data is sent onto the medium one frame at a time
 • Each frame has the destination and source MAC addresses
 • Switch reads the addresses: 
• Use the source MAC address of frame to keep a record of which computer is on which port (switching table) 
• Forwards the frame to the port where the destination MAC can be found  

NIC: Network Interface Card 
  • Most NICs are built into a computer’s motherboard. 
  • Occasionally fail or additional NICs are needed for an application. 
  • It is important to know how to install a new NIC.
Attaching a computer to a network requires a network interface card (NIC).

NIC manufacturers makes sure that every NIC produced has got a unique address. If the addresses aren't unique then network's wont function correctly.

MAC address is stored in read only memory (ROM) on the NIC.

NIC can also function as a gatekeeper.
  • When a frame arrives at a NIC, the NIC check’s the frame’s destination MAC address to see whether it matches it’s built-in MAC address.
  • When the destination MAC address matches the MAC burned-in address (BIA), or the physical address of a NIC, it’s a unicast frame ○ Intended for a single computer.
When the destination is the broadcast address, it’s a broadcast frame. 
• Broadcast frames are intended to be processed by all computers on the network 

 Promiscuous mode – turns off the gatekeeper functions and enables the NIC to process all frames it sees.
• Used by software called a protocol analyzer or packet sniffer.

NICs are often build into the motherboard but they are quite slow and so faster NIC need to be installed.

When we select a NIC, we must make sure to select the correct bus interface.

The NIC driver must be available for your OS.

For desktop a standard NIC is good enough but for servers, a NIC with onboard memory is required to perform faster.

Wireless NIC must be chosen based on the type of wireless AP being used.
Wireless NIC connect to the network using the service set identifier (SSID).
  • SSID is the name assigned to the wireless network.
Router
Connect LANs together to create an internetwork (Network of Networks)
Routers are devices that enable multiple LANs to communicate with one another by forwarding packets from one LAN to another.

Difference between routers and switches:
  • Routers connect LANs while switches connect computers to form LANs.
  • Routers work with IP addresses while switches work with MAC addresses.
  • Routers work with packets, switches with frames.  
  • Routers don’t forward broadcasts, switches do.  
Similarity
  • Routers use routing tables, switches use switching table.
Reserved for private networks.
 The organizations that distribute IP addresses to the world reserves a range of IP addresses for private networks.
• 192.168.0.0 - 192.168.255.255 (65,536 IP addresses) 
• 172.16.0.0 - 172.31.255.255 (1,048,576 IP addresses) 
• 10.0.0.0 - 10.255.255.255 (16,777,216 IP addresses) 

Routers Work with IP Addresses and Routing Tables
  • Default route — where to send a packet when the router doesn’t have an entry in its routing table 
  •  Network unreachable — Message sent when the network can’t be found and no default route
  •  Default gateway — In a computer’s IP address configuration – the IP address of the computer’s router




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