Salesforce.com has an IP address block allocated directly to salesforce.com by the American Registry for Internet Numbers (ARIN).
To provide continuity of service if you utilize email or IP address security filters, white list or otherwise add salesforce.com’s IP address space to your list of trusted addresses
The IP address spaces are as follows:
188.8.131.52/25 East Coast Data Center (set one)
184.108.40.206/25 East Coast Data Center (set two)
220.127.116.11/25 West Coast Data Center (set one)
18.104.22.168/25 West Coast Data Center (set two)
22.214.171.124/25 Singapore Data Center
To clarify, the “0/25” that you see in the ranges refers to an abbreviated form of Classless Inter-domain routing notation. In essence this notation is a network number followed by a “/” and a number , the latter number indicates the number of 1’s (starting a the left most bit i.e MSB – most significant bit) in the subnet mask i.e the number of bits relevant to a network portion of the IP address. So “/25” means 25 bits constitute the subnet mask of 255.255.255.128, and really 25 bits reserved for network address which is identified by performing bitwise “AND” to the full network number.
For example 126.96.36.199/25 means 2 possible networks in the form of 188.8.131.52 and 184.108.40.206 each having possible 126 hosts i.e total 252 hosts or IP addresses per specified range.