DHCP (Dynamic Host Configuration Protocol, Dynamic Host Configuration Protocol) is generally used in large local area network environment, the main role is to centralize the management, assign an IP address, the host to dynamic network environments to obtain an IP address, Gateway address, DNS server addresses and other information, and be able to enhance the utilization of addresses.
DHCP adopts a client / server model, a host address dynamically assigned tasks driven by a network host. When the DHCP server receives the application information from the network host address, the address will be sent to the relevant configuration information to the network host, to achieve a dynamic allocation of network host address information. DHCP has the following features:
1. ensure that any IP address can only be used by a DHCP client at the same time.
2. DHCP should be permanently assigned a fixed IP address to the user.
3. DHCP may be obtained with other methods coexist host IP address (e.g., manually configure the IP address of the host).
4. DHCP server should provide service to existing BOOTP clients. (BOOTP is the predecessor of DHCP)
DHCP assigned IP address has three mechanisms:
1) automatic allocation (Automatic Allocation), DHCP server assign a permanent IP address for the host, once the DHCP client for the first time successfully leased from the DHCP server to the IP address, you can use that address permanently.
2) dynamic allocation (Dynamic Allocation), DHCP server specifies the IP address to a host having a time limit, the time expires, or when the host discard the clear address, which can be used by other hosts.
3) manual distribution (Manual Allocation), the client's IP address is assigned by the network administrator, DHCP server assigned IP address will only tell the client host.
Three types of addresses distribution, only the dynamic allocation can be reused address of the client no longer needed.
NAT (Network Address Translation, Network Address Translation) in 1994 raised. When already allocated in some hosts inside the private network to the local IP address (i.e., used within the private network-specific address only), but now want and host communication on the Internet (not need encryption), the NAT can be used method.
This method requires a router connected to the Internet NAT software installed in the private network. NAT router with a software called NAT router, which has at least one valid external global IP address. In this way, all hosts using local addresses in and outside communication, the NAT router will be in their local address into a global IP address to the Internet and connection.
In a class A address, 10.0.0.0 to 10.255.255.255 a private address.
In the class B address, 172.16.0.0 to 172.31.255.255 a private address.
In a class C address, 192.168.0.0 to 192.168.255.255 is a private address.
(The so-called private address is not used on the Internet, and is used in local area network address)
General home router with NAT function and automatically turns on, its role is to convert the LAN network address into a valid public address. Some routers can be set manually on the NAT be turned on or off; and NAT function of many home routers are not closed, so the NAT option does not exist.