IP Address Check
An IP Address is a 32 bit (IPv4) or 128 bit (IPv6) number that uniquely identifies an internet host. The internet fabric is designed to route all packets correctly to the associated location. The IP address of a website is the address of the associated web server and your IP address shown on this IP Checker tool is the address that your internet provider has given to you or your organzation.
The Internet Assigned Numbers Authority (IANA) is the organization that oversees global IP address allocation. IP address ranges are assigned to countries and internet providers worldwide. Local internet providers finally distribute IP addresses from their allocated address pool to companies or individuals.
Each public IP address is uniqe and points to a specific physical location on earth. This is essiential for the internet to funnction, otherwise it wouldn't be possible for IP packets to reliably reach a specific destination.
While IP addresses can generally be spoofed, it is virtually impossible to hide the physical origin of an internet attack. This is because if someone would fake his IP address, no reply packets would find their way back to him. This means that if you receive an IP packet, you can be quite sure where the packet came from. If it was a malicious data packet it is therefore possible to contact the associated internet provider shown in the IP Checker results and make an abuse report.
A public IP address may be shared by many computers and users, however. This means that if you are attacked by a student on a university, you will get the public IP address of his campus, not the IP address of his computer.
In the case of dynamically assigned IP addresses however, only the internet provider knows which IP address was asseigned to a specific person at a given date and time, and he will not disclose this information without good reason.
A hostname or domain may resolve to more than one IP address, which is commonly used for load sharing and redundancy. IP Checker shows all alternative IP-Addresses in the DNS Records section. The IP Address section uses only one of these IP address, with each consecutive check cycling through all the IP addresses in a round robin manner.
References
IP Address (Wikipedia)