FIREWALL

Firewall :- Firewall is a network device which controls the incoming and outgoing network traffic based on a applied set of rules. Basically this device is used for authentication purpose, also firewall is just like a barrier used in network. Firewall has two properties I mean we have two conditions in firewall one is Denied and another one is Permit and we can only put one condition in action in a network.

Now as you can see in the diagram there is a device between My computer and Computer A and Computer B. So if Computer A and B want to communicate with My computer they have to get authenticated after that they can communicate with My computer otherwise they are not Permitted to connect to My computer. But in case of Computer C there are no any firewall device used between My computer and Computer C so they can connect and communicate between each other without any authentication. Now I think I have clear myself about firewall. Firewall can hardware as well as a software also.
PIX and ASA are the examples of firewall hardware devices.
First Generation
Packet filter :- Firewall technology was first introduce by engineers of  Digital Equipment Corporation in 1988, They developed filter system known as Packet filter firewall.This system was the first generation and now this system is known as technical Internet security. After that AT & T, Bell Labs were continuing their research in packet filtering and developed their own model.
Second Generation
Stateful filters:- Three colleagues were introduce second gen generation of firewall known as Circuit level gateways. Second generation firewall were almost same as first generation firewalls but they work on layer 4 of the OSI model.
Third Generation
Application Layer:- Application firewall is invented by Wie Xu and Peter churchyard and that was also known as Firewall tool kit.
 

ROUTER

Router :- It is layer 3 device of OSI reference model. Router is used to connect or communicate two or more than two different network each other. Router is also responsible for path selection of data to be travel from source to destination without any kind of trouble. Basically routers work on IP addresses. A router never broadcast at all.

 Router are basically of two types
1) Modular:- These router are dynamic in nature. We can change individual port of dynamic router.
2) Non Modular :- These routers are static in nature and we can not change the port of the router. If any of the port is faulty then we must have to change the whole internal part of the router.

According to functionality routers are of three types:-
1) Core Router :- These are the router which became main backbone of the internet. This router must be able to support multiple telecommunication interfaces of highest speed of the internet. And also must be able to forward IP packets are very high speed.
2) Distributed Router :- These Routers distribute the internet. Means these are the routers which are used by the IPs and X-changes to distribute internet connection all over the world.
3) Access Router :- These Routers are for general public, every normal user access the internet from access router. These Routers are basically used in small organizations and homes. These Routers have less functionality then Distributed router and Core router.

SERIES OF ROUTERS
600, 700, 800, 1200, 1400, 1500, 1700, 1800, 1900, 2100, 2300, 2400, 2500, 2600, 2800, 2900, 3200, 3600, 3700, 4100, 4200, 7100, 7200, 7300, 7400, 7500, 7600, 10000, 12000.
From 600 to 2500 series of Routers these all are outdated. From 2600 to 3700 these Routers are Access Routers. From 4100 to 7400 these Routers are known as Distributed Router, 7500 to 12000 these routers are known as Core Routers. From 2600 to 12000 all series of Routers are also known as Modular Routers rest of the routers are Non Modular Routers accept 1800 and 1900.

FUNDAMENTALS OF ROUTER
1) PANEL :- Routers have two panels front and back panel.
Front :- It has only information about the Router's series.
Back :- All ports of the routers are present at the back panel, power supply too.
2) PORT
LAN PORTS :- Ethernet  10 Mbps speed
Fastethernet  100 Mbps speed , Gigaethernet 1000 Mbps speed, 10-Bt  10 base twisted pair cable, AUI 10 Mbps, DB- 15 port.
WAN PORT :- BRI ports and Serial ports. BRI ports are outdated means not in use now a days. So we should only talk about Serial Ports.
Serial ports have some sub parts like Simple serial 60 pins, WIC IT, NM 4 AS, NM 8AS.
Smart Serial have 13 pins, WIC 2T, WIC 3T, WIC 4T.
CONFIGURATION PORTS :- Consol and AUX ports are the ports using for configuration. AUX port is for telephone. Consol port is used for RJ45 connector's devices.
The combination of LAN ports and WAN ports are known as line.
MEMORY IN ROUTER
1) ROM :- Responsible for POST, mini IOS is here in RAM, compression of IOS is known as mini IOS.
2) RAM :- It is used to store the current configurations.
3) FLASH :- After the decompression the IOS is stored in flash memory.
4) NV RAM :- Where we can store our configuration files is known as NVRAM.
There are two types of IOS are in Router.
CISCO IOS :- this is internetwork O.S based on command line interface.
YATA :- this one is Graphical User Interface based.  

SWITCH

SWITCH :- A network switch is used to connect devices together in a computer network. It increase the number of devices within a network. Maximum ports on a switch could be 128. It is a layer 2 device of OSI reference model, also it is a LAN device, It works on MAC addresses. The internal circuit of the switch is like star topology. Port number start from f0/0 to f0/128.

BRIDGE :- It was layer 2 device also. It joint different network. It was only used in LAN level Organization. This was work on MAC addresses, there were 2 collision domain in Bridge. This device is not in use, this is outdated.

FRAME RELAY :- It is a special kind of switch neither work on IP addresses nor on MAC addresses. It works on virtual links. 

HUB

HUB :- Short name of Hirarical Universal Bus, it works on Physical layer of the OSI model. Basically it is a half duplex device, also some time this device is called duffer device because it doesn't have any memory for storage. It also works like repeater. Hub always does broadcasting only, This is the reason, why it has been stoped using now a days.

There is one collision domain in Hubs.

Hubs are replaced by switches. 

Hub have three major types 

1) Active Hub :- having power supply

2)  Passive Hub :- No power supply

3) Intelligent Hub :- Bother the hubs used in this type.

(Collision Domain:- Maximum numbers of devices which can send data without collision simultaneously. 

Amplifier:- It increase the strength of any network. But it doesn't remove the noise that's why it has been stop using. 

Repeater :- This device is used to regenerate the weak and end aged signals, nor it make any noise neither remove the existed noise from the actual signal.    

DEVICES IN NETWORKING , NIC CARD

NIC CARD :- Short name of Network Interface Controller is also known as Network Interface Card,Network adapter, LAN adapter and Physical Network Interface. It is a networking device which connect our computer with the computer network.

As the image tells us that there are three types of NIC Card USB NIC card, Wireless NIC card and old and normal NIC card. At NIC card there is BNC port, RJ45, SC-ST (Suscriber chanel- Straight tip) and a Antina 

STRAIGHT CABLE & CROSS CABLE

Straight Cable :- This cable is use to connect and communicate different addressing system devices.
Like :-
Switch                        to            PC
Modem, Router          to            PC
Hub                            to            PC
Modem, Router          to            Hub
These cables are designed and identify by their colour coding, so lets see the colour coding of straight cable below
White Orange                             White Orange
Orange                                        Orange
White Green                               White Green
Blue                                            Blue
White Blue                                 White Blue
Green                                          Green
White Brown                              White Brown
Brown                                         Brown

Cross cable:- This cable is used to communicate and connect same addressing system devices.
Like :-
PC                           to              PC
Modem, Router       to             PC
Hub                         to             Hub
Switch                     to             Switch
Modem                    to             Router

Now colour coding of cross cable is given below
White Orange                           Orange
Orange                                      White Orange
White Green                             Green
Blue                                          Blue
White Blue                               White Blue
Green                                        White Green
White Brown                            White Brown
Brown                                       Brown

This was all about cables or we can also say communicating medium. 

TWISTED PAIR CABLE

Twisted pair cable is a type of cable  that consist of two independently insulated wires twisted around one another. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction from external sources. There are  four pairs of wire are in a cable. This cable is invented by Alexander Graham Bell.

TYPES OF TWISTED PAIR CABLE

      Shielded Twisted Pair Cable :- As the name tells us that this is shielded means covered. Each pair of cable is covered by an additional copper braid jacket or foil wrapping. This shielding helps to protect the signals on the cable from external interference. This was used in IBM token ring networks. But this cable is expensive then Unsheilded Twisted Pair.

Speed of this cable is 1000 or 1GBps.

UNSHIELDED TWISTED PAIR CABLE:- This cable is used in many Ethernet network and in 

telephone systems. some subtypes of the cables is given below:-

Cat 1                2-4 Mbps speed

Cat 2                6-8 Mbps speed

Cat 3                10-20 Mbps speed    ETHERNET CABLES 

Cat 4                40-60 Mbps speed 

Cat 5                100 Mbps speed        FASTETHERNET CABLES 

Cat 5 e             150 Mhz speed          GIGAETHERNET CABLES

Cat 6                1000 Mbps speed