Each system that would want to do name resolution would need to have this hosts file but once you create one you can just copy it to other systems. Then instead of entering the command:
Medium-size Switched Network Construction Network Address Translation We will describe the whole process of deploying Internet access by adding services to your Internet router in the form of DHCP servers, and network address translation.
You will be able to touch and feel the whole process by configuring these functions on a Cisco router. Network Address Translation The number of IP addresses allocated by the Internet service provider will typically be small. So most organizations, if not all, use a private addressing scheme inside of their network and will require network address translation for connectivity to the public network, and that device in the middle would implement the translation and it would translate back for return traffic into the private addressing scheme.
When talking about NAT, it is important to understand the terminology. You will have global and local addresses, global meaning public addresses that make sense out in the public Internet and local addresses which are related to the private addressing.
Another concept is that of inside and outside devices. An inside device will be physically located in the internal network, whereas an outside device will be physically located somewhere else.
Another concept is that of address assignments or mappings; they can be static or dynamic: Port Address Translation Outbound traffic that is going toward the Internet typically uses dynamic assignment of public IP addresses.
This means that one machine in the inside could be using a certain public address when going out today, but a different address when going out tomorrow. This allows for more flexibility in reusing the public address ranges.
However, those public address ranges are typically very small. A lot of times it is only one public address that you can use and that address is already assigned to the public interface of the perimeter device.
You will need to reuse that public IP address for all of the internal machines. That is why we have port address translation or PAT. Multiple private addresses can reuse the same public address as indicated in that NAT table there, but the NAT device will include a port number to the translation.
The port number is always different and it will be the tiebreaker to identify which private address is using which instance of the one public address. Translating Inside Source Address Here is how it works in a one-to-one translation environment.
The source machine will send a packet with the private address which will hit the NAT device. If there is one, it will use it; if there is none, then it will dynamically assign a public address and forward a packet.
When the destination replies, the old source address becomes the destination address now; it will eventually hit the NAT device again. When it finds it, it will simply translate that public address of the destination into a private address. It then forwards a packet back to the original source and this same thing happens for all the packets and all of the senders where each sender will use a different public IP.
Overloading an Inside Global Address The previous example is not sustainable in an Internet scenario. That is why we need port address translation, sometimes known as NAT overload.
The process is the same but now the path device will use an expanded NAT table that will include ports. Notice how the source ports are translated at the NAT device, which will control uniqueness of these ports to be able to know which private addresses are using which instance of the public address.
Since the source ports travel with the packet, return traffic will contain the same information and that is how the PAT device will know who to deliver the packet to.
Configuration and Commands SDM simply hides the complexity of commands, but it will generate and create those commands and deliver them to the router. Here is a samble configuration with IP NAT overloading, which shpuld be applyed to the router from the image above.In some situations, you may find it necessary to configure both static and dynamic Network Address Translation (NAT) commands on a Cisco router.
This document explains how you can do this, and gives a sample scenario. Basically, Network Address Translation (NAT) allows a single device, such as a router, to act as an agent between the Internet (or “public network”) and a local (or “private”) network.
It is a temporary workaround to the immediate problem of too many hosts and not enough IP addresses. This is known also as PAT (Port Address Translation), single address NAT or port-level multiplexed NAT. In overloading, each computer on the private network is translated to the same IP address (), but with a different port number assignment.
Welcome to the Cisco Networking Professionals Ask the Expert conversation. This is an opportunity to discuss with Cisco experts Aamer Akhter and Kevin Eckhardt about the Network Address Translation (NAT) which is designed for IP address simplification and conservation.
Network Address Translation (NAT) allows private IP addresses to be translated into Internet-routable IP addresses A challenge with basic NAT, however, is that there is a one-to-one mapping of inside local addresses to inside global addresses, meaning that a company would need as many publicly routable IP addresses as it had internal devices .
Firewall interfaces (ports) enable a firewall to connect with other network devices and with other interfaces within the firewall. The following topics describe the interface types and how to configure them.