Special IP Addresses – 127.0.0.1; 0.0.0.0; 10.0.0.1;


IP 127.0.0.1
Definition: 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 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

10.0.0.1
Definition: 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.

source: http://compnetworking.about.com/od/workingwithipaddresses/g/127_0_0_1_def.htm

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