Question

How do NAT and DHCP conserve IP addresses?

Answer 1

How do NAT and DHCP conserve IP addresses?

NAT and PAT. The concept of NAT is based on the fact that every computer sending traffic outside its LAN to the Internet must be assigned a routable IP address. To conserve IP addresses, LAN users make use of a range of private IP addresses for routing local traffic.

This module describes how to configure Network Address Translation (NAT) for IP address conservation and how to configure inside and outside source addresses. This module also provides information about the benefits of configuring NAT for IP address conservation.

NAT enables private IP internetworks that use nonregistered IP addresses to connect to the Internet. NAT operates on a device, usually connecting two networks. Before packets are forwarded onto another network, NAT translates the private (not globally unique) addresses in the internal network into legal addresses. NAT can be configured to advertise to the outside world only one address for the entire network. This ability provides more security by effectively hiding the entire internal network behind that one address.

NAT is also used at the enterprise edge to allow internal users access to the Internet. It allows Internet access to internal devices such as mail servers.

DHCP is an abbreviation for Dynamic Host Configuration Protocol. It is an application layer protocol used by hosts for obtaining network setup information. The DHCP is controlled by DHCP server that dynamically distributes network configuration parameters such as IP addresses, subnet mask and gateway address.

1. DHCPDISCOVER: When a new node is connected to the network, it broadcasts the DHCPDISCOVER message which contains the source address as 0.0.0.0 to every node on the network including server. DHCP server on receiving the message, returns the DHCPOFFER message to the requested host which contains the server address and new IP address to the node.
2. DHCPOFFER: If there are multiple servers on the network, host receives multiple DHCPOFFER messages. It is up to the host to select a particular message.
3. DHCPREQUEST:  The requested host on receiving the offer message, it again broadcasts the DHCPREQUEST message on the network with the address of the server whose offer message is accepted by the host. The server which pertains to that server address sent by the host checks whether the address to be assigned to the node is available in the data storage.
4. DHCPACK : If the address is assigned , it marks the IP address in the storage as unavailable to ensure consistency. Now, the server sends DHCPACK packet to the requested host which contains network information(IP address, subnet mask, gateway address). In case, if the address is assigned to other machine meanwhile, then the server sends the packet DHCPNAK to the requested host indicating that the IP address is assigned to some other machine.
5. DHCPRELEASE : And finally, If the host wants to move to other network or if it has finished its work, it sends the DHCPRELEASE packet to the server indicating that it wants to disconnect. Then the server marks the IP address as available in the storage so that it can be assigned to other machine.