Access management method, device and system as well as access device for information system

The invention provides an access management method, a device and a system as well as an access device for an information system, wherein the method comprises: examining and handling according to a domain name carried in a domain name system DNS request massage from clients, and forwarding a DNS request massage passing the examination to a DNS server; adding an IP address corresponding to the domain name carried in the DNS request massage passing the examination according to a DNS response massage from the DNS server; and carrying out examining on the IP address according to an IP massage from the clients and an accessible IP list, and allowing the IP massage passing the examination to access the information system resources in the information system server. The device comprises a first examining module, a first appending module and a second examining module. The access device comprises an access management device of the information system. The invention also provides an access management system of the informa