公用IP地址和专用IP地址

电玩女神 2022-08-13 11:43 299阅读 0赞

###### What Is a Public IP Address? ######

An IP address is considered public if the IP number is valid and falls outside any of the IP address ranges reserved for private uses by Internet standards groups. (See private IP addresses)   
Public IP addresses are used by Internet servers including those for Web sites and DNS servers), network routers or any computer connected directly to the Internet via a modem.  
Each public IP is assigned to a range or block of addresses. The Internet Assigned Numbers Authority (IANA) controls ownership of these IP ranges and assigns each block to organizations such as Internet Service Providers (ISPs) who in turn allocate individual IP addreses to customers.

###### What Is a Private IP Address? ######

An IP address is considered private if the IP number falls within one of the IP address ranges reserved for private uses by Internet standards groups. These private IP address ranges exist:

*  **A类：10.0.0.0    through 10.255.255.255 **
 *  **B类：169.254.0.0 through 169.254.255.255 ( APIPA only) **
 *  **　　   172.16.0.0  through 172.31.255.255 **
 *  **C类：192.168.0.0 through 192.168.255.255 **

Private IP addresses are typically used on local networks including home, school and business LANs including airports and hotels.   
Devices with private IP addresses cannot connect directly to the Internet. Likewise, computers outside the local network cannot connect directly to a device with a private IP. Instead, access to such devices must be brokered by a router or similar device that supports Network Address Translation (NAT). NAT hides the private IP numbers but can selectively transfer messages to these devices, affording a layer of security to the local network.   
Standards groups created private IP addressing to prevent a shortage of public IP addresses available to Internet service providers and subscribers.

###### IP: 10.0.0.1 ######

The IP address 10.0.0.1 is a default for some types of network routers including Cisco brand routers. This address may also be used by network servers.   
10.0.0.1 is sometimes called a default gateway address as it typically represents the local side of a router's connection to the Internet. 10.0.0.1 is more commonly found in business networks than in homes, which tend to use routers having default addresses in the 192.168.x.x series. Both the 10.x.x.x and 192.168.x.x series are private IP address ranges.   
For students: in classful IP networks, 10.0.0.1 is a class A address with default subnet mask 255.0.0.0.

###### IP: 127.0.0.1 ######

The IP address 127.0.0.1 is a special purpose address reserved for use on each computer. 127.0.0.1 is conventionally a computer's loopback address.   
Network software and utilities can use 127.0.0.1 to access a local computer's TCP/IP network resources. Messages sent to loopback IP addresses like 127.0.0.1 do not reach outside to the local area network (LAN) but instead are automatically re-routed by the computer's own network adapter back to the receiving end of the TCP/IP stack.  
Typically all IP addresses in the range 127.0.0.1 - 127.255.255.255 are reserved for private use, but 127.0.0.1 is by convention the loopback address in almost all cases.

###### IP: 0.0.0.0 ######

Definition: IP address numbers range from 0.0.0.0 up to 255.255.255.255. The IP address 0.0.0.0 has special meaning on computer networks.   
Computers normally show an address of 0.0.0.0 when they are not connected to a TCP/IP network. Having this address, a computer cannot be reached or communicate with any other devices over IP.  
TCP/IP software applications also use 0.0.0.0 as a programming technique to monitor network traffic from any valid IP address. While connected computers do not use this address, messages carried over IP sometimes include 0.0.0.0 inside the header when the source of the message is unknown.  
  
Troubleshooting IP Address Problems  
If a computer is properly configured for TCP/IP networking yet still shows 0.0.0.0 for an address, try the following to troubleshoot this problem and obtain a valid address: ? For networks with dynamic (DHCP) address support, release and renew the computer's IP address.   
For networks that require static IP addressing, configure a valid IP address on the computer

###### APIPA - Automatic Private IP Addressing ######

A feature of Microsoft Windows, APIPA is a DHCP failover mechanism for local networks. With APIPA, DHCP clients can obtain IP addresses when DHCP servers are non-functional. APIPA exists in all modern versions of Windows except Windows NT.   
When a DHCP server fails, APIPA allocates IP addresses in the private range 169.254.0.1 to 169.254.255.254. Clients verify their address is unique on the network using ARP. When the DHCP server is again able to service requests, clients update their addresses automatically.  
In APIPA, all devices use the default network mask 255.255.0.0 and all reside on the same subnet.  
APIPA is enabled on all DHCP clients in Windows unless the computer's Registry is modified to disable it. APIPA can be enabled on individual network adapters.  
Also Known As: Automatic Private IP Addressing; AutoNet

Examples: Because APIPA uses IP addresses in the private Class B space, APIPA is a feature generally only useful on home or other small intranet LANs.

参考：

http://compnetworking.about.com/od/routers/g/10\_0\_0\_1\_def.htm