NAT

-NAT is the process of mapping one IP to another IP
-NAT is used to save public IP
-It provides security by hiding the internal IP

Types of NAT

-Static NAT (one to one)

• One private IP is mapped to one public IP
• Generally used for hosting public servers

-Dynamic NAT (many to many)

• Many private IPs are mapped to many public IPs
• Can only be configured for outbound trafiic

-PAT (many to one)

• Many private IPs are mapped to one public IP
• All users can access internet at the same time
• Can only be configured for outbound traffic

-Practically what we do is dynamic source or destination NAT which depends on the purpose
-In case of accessing a public hosted web server, we are using a dynamic destination NAT rule, where all the requests coming to the public IP of that web server will be mapped to a internal private IP
-A group of internal users accessing internet can be done using a dynamic source NAT rule, where all the internal requests are mapped to a external public IP

Basic command line and run utilities

cmd utilities :

ipconfig - network configuration details
nslookup - dns details
ping - checks connectivity
wuauclt /detectnow - checks Windows updates from WSUS server
ipconfig /flushdns - flush dns entries
ipconfig /registerdns - register dns entries
gpupdate /force - updates group policies

run utilities :

mstsc - RDP
windowsupdate.log - log file for Windows updates
services.msc - services
gpmc.msc - group policy management
dsa.msc -AD users and computers
inetcpl.cpl - Internet properties
diskmgmt.msc - disk management
compmgmt.msc - computer management
devmgmt.msc - device manager
eventvwr.msc - event viewer
msconfig - system configuration
regedit - registry editor

Router

-Router is a Layer -3 device (i.e, works in network layer)
-Main function of a router is routing/ internetworking
-It can be a dedicated hardware router or a software router
-In a production environment we use dedicated hardware routing devices (eg: CISCO, JUNIPER etc.)
-A router does packet switching, i.e, from one interface to another interface of the same router
-It also does packet forwarding
-It performs best path selection
-Considering the CISCO hierarchical model we have different types of routers

• Access layer routers
• Distribution layer routers
• Core layer routers

-A hardware router can be of two types

• Modular router (up-gradable) 
• Fixed router ( not up-gradable)

VLAN

-VLAN stands for Virtual LAN
-VLAN provides L2 security
-Divides a single broadcast domain into multiple broadcast domains
-By default all ports of a the switch are in VLAN 1
-VLAN 1 is known as administrative VLAN or management VLAN
-VLAN can be created from 2 - 1001

Static VLAN

-Static VLANs are port based and hence they are also called as port based VLANs
-Ports have to be manually assigned to a VLAN
-A port can be a member of a single VLAN

Dynamic VLAN

-Dynamic VLANs are based on the MAC address of a device
-Switch automatically assigns the port to a VLAN
-Each port can be a member of multiple VLANs
-For dynamic VLAN configuration, a software called VMPS (VLAN Management Policy Server) is needed

OSI layers

OSI stands for Open Systems Interconnect is a conceptual model that standardize the communication between networked systems. The 7 layers of OSI model is as follows :

-Physical layer
-Data link layer
-Network layer
-Transport layer
-Session layer
-Presentation layer
-Application layer

IP address

IPV4 - 32 bit address
IPV6 - 128 bit address

Public addresses

Format : x.x.x.x (where each 'x' is a 8 bit value)
IPV4 is divided into the following 5 classes, which is based on the decimal value of the first octet

Class A :     0 - 126.x.x.x (first octet forms network ID-NID and last three octets forms host ID-HID)
Class B : 128 - 191.x.x.x (first 2 octets forms NID and last 2 octets forms HID)
Class C : 192 - 223.x.x.x (first 3 octets forms NID and last octet forms HID)
Class D : 224 - 239.x.x.x (used for multicast)
Class E : 240 - 255.x.x.x (used for research purpose)

Private addresses

Class A
Range : 10.0.0.0 - 10.255.255.255
Total number of networks : 1

Class B
Range : 172.16.0.0 - 172.31.255.255
Total number of networks : 16

Class C
Range : 192.168.0.0 - 192.168.255.255
Total number of networks : 256

RAID

RAID stands for Redundant Array of Inexpensive/ Independent Disks. There are different RAID levels and the level you choose for your system depends on the amount of storage you require and the way you access your data and several other factors like cost, redundancy etc. Common RAID levels are 0, 1 and 5.

RAID 0

-Data stripping

-Improved performance

-No redundancy

RAID 1

-Mirroring

-Redundant

RAID 5

-Data stripping + evenly distributed parity

-Redundancy + improved performance

-Minimum 3 hard disks required

RAID is mostly used in a production setup or where redundancy and performance is a major concern. It is configured by using RAID controllers. For example, in the case of Dell PowerEdge R710 servers, RAID is configured using PERC (PowerEdge Raid Controller). Press Ctrl+R to access the PERC BIOS Configuration Utility after starting or restarting the PowerEdge server.