It consists of standard firewalls and proxy servers at the Internet gateways. The system also selectively engages in DNS poisoning when particular sites are requested. The government does not appear to be systematically examining Internet content, as this seems to be technically impractical.[50] Researchers at the University of California, Davis, and at the University of New Mexico said that the censorship system is not a true firewall since banned material is sometimes able to pass through several routers or through the entire system without being blocked.[34] Details for some commonly used technical methods for censoring are:[51]