Besides the two basic security mechanisms that 802.11 provides, many products implement MAC address filtering. The MAC address filter contains the MAC addresses of the wireless NICs that may associate with any given AP. Some vendors provide tools to automate the entry and update processes. A MAC filter does not provide very strong security because it is easy to discover known good MAC addresses with a sniffer. Then, using Linux drivers available on the Internet for most 802.11 client access cards, one can configure the sniffed MAC address into the card and gain access to the network. The other two steps mentioned by the Wi-Fi Alliance, use of session keys and a VPN system, are good, workable solutions for securing Wi-Fi.