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DNS and BIND 5th Edition_7

Tham khảo tài liệu 'dns and bind 5th edition_7', công nghệ thông tin, hệ điều hành phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | DNS BIND -f DNS and BIND- C SEARCH Chapter 10 Advanced Features and Security 10.7 Building Up a Large Site-wide Cache with Forwarders Certain network connections discourage sending large volumes of traffic off-site either because the network connection is pay-per-packet or because the network connection is a slow link with a high delay like a remote office s satellite connection to the company s network. In these situations you ll want to limit the off-site DNS traffic to the bare minimum. BIND provides a mechanism to do this forwarders. If you designate one or more servers at your site as forwarders all the off-site queries are sent to the forwarders first. The idea is that the forwarders handle all the off-site queries generated at the site building up a rich cache of information. For any given query in a remote domain there is a high probability that the forwarder can answer the query from its cache avoiding the need for the other servers to send packets off-site. Nothing special is done to these servers to make them forwarders you modify all the other servers at your site to direct their queries through the forwarders. A primary master or slave name server s mode of operation changes slightly when it is directed to use a forwarder. If the requested information is already in its database of authoritative data and cache data it answers with this information this part of the operation hasn t changed. However if the information is not in its database the name server will send the query to a forwarder and wait a short period for an answer before resuming normal operation and contacting the remote servers itself. What the name server is doing that s different is sending a recursive query to the forwarder expecting it to find the answer. At all other times the name server sends out nonrecursive queries to other name servers and deals with responses that only refer to other name servers. For example here is the forwarders conf file statement - and the equivalent BIND 4