Network Devices

Layer 1 - Physical Layer

Layer 2 - Data Link Layer

Layer 3 - Network Layer

Layer 1 - Physical Layer

A hub (A.K.A. Network Hub) works at the Physical Layer (Layer 1) of the OSI model.
Used to set up LAN
Has multiple ports
- $\to$ Connect another hub and extend the network as necessary.
Star topology
When a packet arrives at one port, it is copied to all the other ports so that all segments of the LAN can see all packets.
- Every data the hub receives will be broadcasted to all the other nodes in the network. (Drawback of the hub)
Computer (or other device) and the hub will be connected using Ethernet Straight Through Cable.
Pros and Cons
Pros:
- Cheaper than switches
- Works good for smaller network
Cons:
- Issues with broadcast
  If the network gets bigger, broadcast issues will get even worse.
- No memory (Not intelligent)
  Hubs will simply broadcast everything it receives, but will not store any information since there’s no memory in them.
- Normally runs in hafl-duplex mode.
  This is why switches (full-fuplex) are dominating.

The data signals generally become too weak or corrupted if they travel a long distance.
Repeater regenerates the signal over the same network. It does not amplify the signal. (Does not increase the volume)
Operates at the Physical Layer (Layer 1).
Has only two ports.
Use case:
When two different buildings want to construct a same LAN, bridge can help since the signal generated from the source host in building A needs to reach the destination host in building B without loosing its signal.

A switch is a Data Link Layer (Layer 2) networking device that connects devices on a computer network to establish a Local Area Network (LAN).
Switches connect devices that are belonging to the same network.
A switch is a mechanism that allows us to interconnect links to form a larger network.
A switch is a multi-input, multi-output device that transfers packets from an input to one or more outputs.
The core job of a switch is to take packets that arrive on an input and forward (or switch them to the right output so that they will reach their appropriate destination.
Unlike hub, switch has memory stores MAC Addresses Table in its memory.
```
xxxxxxxxxx
4
1
MAC ADDRESS           INTERFACE / PORT
2
====================  ================
3
AA-AA-AA-AA-AA-AA     1
4
BB-BB-BB-BB-BB-BB     19
```
When Host-A (AA-AA-AA-AA-AA-AA) that is connected to the switch port 1 wants to send a data to Host-B (BB-BB-BB-BB-BB-BB) that is connected to the switch port 19, switch consults its MAC Address Table and forwards the data it received from Host-A exactly to Host-B. (It does not simply broadcast every time like hubs do.)
Don’t be confused! Switches are capable of unicasting, multicasting, and broadcasting.

Hub vs. Switch

Hub	Switch
Layer 1 device (Physical Layer)	Layer 2 device (Data Link Layer)
Has NO memory	Has memory and stores MAC Address Table
NOT intelligent	Intelligent
Floods the network due to broadcasting	Can do unicasting, multicasting, broadcasting
High security risks	Low security risks
Less efficient	More efficient
Half duplex	Full Duplex (Tx/Rx at the same time)

Bridge = Repeater + (Functionality of reading MAC address)
Also used for interconnecting two LANs on the same protocol.
Has only two ports like repeaters.
Two types of bridges:
- Transparent Bridges
  The bridge in which the stations (or hosts) are completely unaware of the bridge’s existence. Meaning, it’s not necessary to do any configurations in the stations
  - For a router, we give the IP address of the interface as the default gateway for all the stations or PCs. (This is not necessary in bridges.)
  Reconfiguration of the stations is unnecessary even if bridge is added or removed from the network.
- Source Routing Bridges
  Routing operation is performed by the source station (or host) and the frame specifies which route to follow.
  - Source has the routing information that designates how to get to the destination.
Bridge vs. Router
- A bridge interconnects LANs that are running in the same protocol and it is a Layer 2 device, it deals with the MAC addresses only.
- A router interconnects two different LANs that have two different protocols and it is a Layer 3 device, it deals with the IP addresses.

A router is a Network Layer (Layer 3) networking device that forwards data packets between computer networks.
- A router connects two or more different Local Area Networks (LANs).
- One interface is part of one LAN, another interface is part of another LAN.
A router is connected to at least two networks, commonly two LANs or WANs, or a LAN and its ISP’s network (i.e., Internet).
Has memory and stores Routing Table in its memory
Default gateway is the IP address of the first router that the packet to be sent out to the Internet is going to hit.

Switch vs. Router

Switch	Router
Connect many devices together within a LAN	Connects a LAN to other LANs
Layer 2 device (Data Link Layer)	Layer 3 device (Network Layer)
Has memory and stores MAC Address Table	Has memory and stores Routing Table
Forwarding decisions are made on MAC address	Forwarding decisions are made on IP address
Full Duplex	Full Duplex
LAN	LAN, MAN, and WAN