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5c526acb82c882e41b655c31f5fa4425c87b671cMark Andrews<TITLE> Section 5. The BIND 9 Lightweight Resolver</TITLE></HEAD>
5c526acb82c882e41b655c31f5fa4425c87b671cMark AndrewsThe BIND 9 Lightweight Resolver</H1>
5c526acb82c882e41b655c31f5fa4425c87b671cMark Andrews5.1 The Lightweight Resolver Library</H3>
5c526acb82c882e41b655c31f5fa4425c87b671cMark AndrewsTraditionally applications have been linked with a stub resolver library that sends recursive DNS queries to a local caching name server.</P>
5c526acb82c882e41b655c31f5fa4425c87b671cMark AndrewsIPv6 introduces new complexity into the resolution process, such as following A6 chains and DNAME records, and simultaneous lookup of IPv4 and IPv6 addresses. These are hard or impossible to implement in a traditional stub resolver.</P>
5c526acb82c882e41b655c31f5fa4425c87b671cMark AndrewsInstead, BIND 9 provides resolution services to local clients using a combination of a lightweight resolver library and a resolver daemon process running on the local host. These communicate using a simple UDP-based protocol, the "lightweight resolver protocol" that is distinct from and simpler than the full DNS protocol.</P>
5c526acb82c882e41b655c31f5fa4425c87b671cMark Andrews5.2 Running a Resolver Daemon</H3>
5c526acb82c882e41b655c31f5fa4425c87b671cMark AndrewsTo use the lightweight resolver interface, the system must run the resolver daemon <CODE CLASS="Program-Process">
5c526acb82c882e41b655c31f5fa4425c87b671cMark Andrewslwresd</CODE>
5c526acb82c882e41b655c31f5fa4425c87b671cMark AndrewsApplications using the lightweight resolver library will make UDP requests to the IPv4 loopback address (127.0.0.1) on port 921. The daemon will try to find the answer to the questions "what are the addresses for host <EM CLASS="URL">
5c526acb82c882e41b655c31f5fa4425c87b671cMark Andrews?" and "what are the names for IPv4 address 204.152.184.79?"</P>
5c526acb82c882e41b655c31f5fa4425c87b671cMark AndrewsThe daemon currently only looks in the DNS, but in the future it may use other sources such as <EM CLASS="grammar_literal">
5c526acb82c882e41b655c31f5fa4425c87b671cMark Andrews, NIS, etc.</P>
5c526acb82c882e41b655c31f5fa4425c87b671cMark Andrewslwresd</CODE>
5c526acb82c882e41b655c31f5fa4425c87b671cMark Andrews daemon is essentially a stripped-down, caching-only name server that answers requests using the lightweight resolver protocol rather than the DNS protocol. Because it needs to run on each host, it is designed to require no or minimal configuration. It uses the name servers listed on <CODE CLASS="Program-Process">
5c526acb82c882e41b655c31f5fa4425c87b671cMark Andrewsnameserver</CODE>
5c526acb82c882e41b655c31f5fa4425c87b671cMark Andrews as forwarders, but is also capable of doing the resolution autonomously if none are specified.</P>
5c526acb82c882e41b655c31f5fa4425c87b671cMark Andrews<p>Return to <A href="Bv9ARM.html">BIND 9 Administrator Reference Manual</A> table of contents.</p>