1. What is IP address, and what is the difference between IP address and domain name?
Answer: IP address is Internet protocol address which works on ISO/OSI model network layer for identifying network address of network layer equipment. IPv4 address in current use is composed of four digits between 0 and 255, for example 155.226.1.1. Description in digits is not convenient to use and remember compared to description in language. Therefore, people use domain name to identify network address, and build correspondence between domain name and IP address (by domain name server). The format of domain name is www.cnnic.cn.

2. What are the requirements for application for IP addresses?
ISPs, enterprises, institutions and organizations of certain scales that need IP addresses in Mainland China can apply for IP addresses. CNNIC only accepts applications for IPv4 address of no more than 4 Cs (1024 IP addresses) from April 15, 2011.

3. What is IPv6 address? How to apply for it?
IPv6 address is the sixth version of IP address and uses 128 bits for the addresses (IPv4 is 32 bits), which can effectively address the grave shortage of IPv4 address. Organizations can apply to CNNIC for IPv6 address. Generally speaking, IPv6 addresses allocated at present have a minimum unit of /32.

4. What is AS number? What are the requirements for the application?
AS number is the autonomous system number to identify an independent autonomous system. In the same autonomous system, the same interior routing protocol is utilized. Exterior routing protocol is used between autonomous systems (usually BGP protocol).
Organizations that are to apply for an AS number should have network interconnections with two or more ISPs　that have different AS numbers. Applicants are to carry out, the same time as ISP, exterior routing operating BGP within three months.

5. What is Reverse DNS Delegation? How to apply for it?
Contrary to forward DNS resolution, Reverse DNS Delegation provides correspondence of IP addresses with domain name. Format of reverse DNS is: X.X.X.in-addr.arpa. Currently, many network service providers request IP addresses to have results of Reverse DNS Delegation, or they will not provide service.
CNNIC provides reverse DNS service for allocated addresses. The smallest unit for resolution is /24. Please fill in Application Form of Reverse Domain Name System and e-mail it to us when you need the service.