How To Change A Public Network To A Private

To access the Cyberspace, one public IP address is needed, but we can use a private IP accost in our private network. The thought of NAT is to allow multiple devices to access the Internet through a single public address. To achieve this, the translation of a private IP address to a public IP address is required. Network Address Translation (NAT) is a procedure in which 1 or more local IP address is translated into one or more Global IP address and vice versa in lodge to provide Internet access to the local hosts. Also, information technology does the translation of port numbers i.eastward. masks the port number of the host with another port number, in the packet that will be routed to the destination. It then makes the corresponding entries of IP address and port number in the NAT table. NAT generally operates on a router or firewall.

Network Accost Translation (NAT) working –
Generally, the border router is configured for NAT i.e the router which has i interface in the local (inside) network and i interface in the global (exterior) network. When a package traverse outside the local (inside) network, then NAT converts that local (private) IP address to a global (public) IP accost. When a packet enters the local network, the global (public) IP address is converted to a local (individual) IP address.

If NAT runs out of addresses, i.e., no accost is left in the pool configured and then the packets will exist dropped and an Internet Control Message Protocol (ICMP) host unreachable packet to the destination is sent.

Why mask port numbers ?
Suppose, in a network, ii hosts A and B are connected. Now, both of them request for the aforementioned destination, on the same port number, say chiliad, on the host side, at the aforementioned time. If NAT does only translation of IP addresses, and so when their packets will arrive at the NAT, both of their IP addresses would exist masked by the public IP address of the network and sent to the destination. Destination will send replies to the public IP address of the router. Thus, on receiving a reply, information technology will exist unclear to NAT as to which reply belongs to which host (because source port numbers for both A and B are the same). Hence, to avoid such a problem, NAT masks the source port number every bit well and makes an entry in the NAT tabular array.

NAT inside and outside addresses –
Within refers to the addresses which must be translated. Exterior refers to the addresses which are not in control of an organization. These are the network Addresses in which the translation of the addresses will be done.

Within local accost – An IP address that is assigned to a host on the Inside (local) network. The address is probably not an IP address assigned past the service provider i.east., these are private IP addresses. This is the within host seen from the within network.
Inside global address – IP accost that represents one or more inside local IP addresses to the outside world. This is the inside host equally seen from the outside network.
Exterior local address – This is the bodily IP address of the destination host in the local network later on translation.
Outside global accost – This is the outside host as seen from the outside network. Information technology is the IP address of the outside destination host earlier translation.

Network Address Translation (NAT) Types –
In that location are 3 ways to configure NAT:

Static NAT – In this, a single unregistered (Private) IP address is mapped with a legally registered (Public) IP address i.eastward one-to-one mapping betwixt local and global addresses. This is generally used for Web hosting. These are not used in organizations as there are many devices that will demand Cyberspace access and to provide Internet admission, a public IP address is needed.
Suppose, if in that location are 3000 devices that need access to the Internet, the organization has to buy 3000 public addresses that will be very costly.
Dynamic NAT – In this type of NAT, an unregistered IP accost is translated into a registered (Public) IP address from a pool of public IP addresses. If the IP accost of the pool is not gratis, then the parcel will be dropped every bit merely a stock-still number of private IP addresses tin exist translated to public addresses.
Suppose, if there is a pool of 2 public IP addresses then only 2 private IP addresses tin can be translated at a given time. If tertiary private IP address wants to access the Internet then the bundle will be dropped therefore many private IP addresses are mapped to a pool of public IP addresses. NAT is used when the number of users who desire to access the Internet is fixed. This is too very plush as the organisation has to buy many global IP addresses to make a pool.
Port Address Translation (PAT) – This is besides known as NAT overload. In this, many local (private) IP addresses tin can be translated to a single registered IP address. Port numbers are used to distinguish the traffic i.e., which traffic belongs to which IP address. This is well-nigh frequently used as information technology is toll-constructive as thousands of users can be connected to the Internet by using only i real global (public) IP accost.

Advantages of NAT –

NAT conserves legally registered IP addresses.
It provides privacy as the device's IP address, sending and receiving the traffic, will be hidden.
Eliminates address renumbering when a network evolves.

Disadvantage of NAT –

Translation results in switching path delays.
Certain applications will not office while NAT is enabled.
Complicates tunneling protocols such as IPsec.
Also, the router being a network layer device, should not tamper with port numbers(transport layer) but it has to do so because of NAT.