HTTP header fields are components of the message header of requests and responses in the Hypertext Transfer Protocol (HTTP). They define the operating parameters of an HTTP transaction. The header fields are not directly displayed by normal web browsers like Internet Explorer, Google Chrome, Firefox etc. Below is the HTTP Header information of os.51cto.com:

Domain Name Systes (DNS) translates easily memorized domain names to the numerical IP addresses needed for the purpose of locating computer services and devices worldwide. There are total 6 DNS record(s) of 51cto.com.