Other Resolver Parameters BIND Configuration

cat etcresolv.conf for the resolver−only IRIX system ; ;Default domain to append to names domain myschool.scps.edu ; ;This is name server host nameserver 146.98.1.12 ;pegasus.mys chool.scps.edu nameserver 146.98.1.17 ;orion.mysch ool.scps.edu nameserver 128.228.1.10 ;acme.ucc.c uny.edu nameserver 147.225.1.2 ;nis.ans.net ; hostresorder local bind Two universally supported entries are: nameserver 1. The name servers are queried in the order that they appear in the file. If the local host is one of the name servers, the generic local host address 127.0.0.1 is used. domain 2. The entry defines the default domain name to be appended to the relative host names if specified without a trailing dot. The other domain name combinations are also queried. The presented entry hostorder is UNIX flavor−specific, and is obsolete. In this example it defines the order of how the host names will be resolved: first by looking into the local etchosts configuration file and then using DNS BIND. Although all new UNIX releases support this approach name resolution among DNS, NIS, or the local host database, it is provided in a different way, by using the etcnsswitch.conf file this is discussed in Chapter 17, along with other NIS issues. Unfortunately, some BIND releases did not work properly on all UNIX platforms. For example, SunOS required that NIS be implemented, or it would ignore DNS. BIND 4.8.1 did not properly support local host address 127.0.0.1; appropriate patches were provided. Later BIND releases overcame these problems.

16.2.2.2 Other Resolver Parameters

Two basic resolver directives, domain and nameserver, are universally supported and are sufficient to fully configure the resolver. However, additional resolver parameters introduced later improved overall resolver characteristics, primarily by making it more flexible. The additional resolver parameters and the corresponding directives to specify them are: search • The list of the domain names to append to the relative host name, similar to the domain directive, except that it can take multiple domains as arguments; mutually exclusive with the domain directive BIND 4.8.3 and later versions. sortlist • Specifies preferable resolver network numbers if multiple IP addresses are received as a response to a query. The resolver will sort received addresses appropriately, for example: sortlist 128.44.23.0255.255.255.0 specifies the subnetted class B network 128.44.23.0 identified by the mask 255.255.255.0 separated by the slash ; if the whole network is specified there is no 379 options ndots • Specifies the number of dots . an argument must have in it so that the resolver will look for it before applying the search list BIND 4.9.3 and later. options debug • Turns on debugging output in the resolver BIND 4.9.3 and later. ; and • Specify comment lines in the resolver configuration file; comments with have been allowed since BIND 4.9.3. The default search algorithm was also changed with the release of BIND 4.9.3; the domain directive specifies the default search list. The default search list originally included the default domain and each of its parent domains with two or more labels. For each relative host name host name without a trailing dot, first a full domain is appended, then its parent domain, then the next parent domain, and so on until the last two labels. The single last label is never appended. The host name is looked up as is after the search list is applied, and then only if the host name contains at least one dot. A search is terminated as soon as a positive response to the resolver query has been obtained. With BIND 4.9.3, the default search list includes only the default domain; in addition, the search list is applied after the host name is tried as is. Obviously, the search directive should be used for more detailed searching.

16.2.3 Name Servers