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NAME

dns - display DNS information and control DNS subsystem

SYNOPSIS

dns info dns flush

DESCRIPTION

The dns family of commands provides a means to monitor and control DNS name resolution.

USAGE

dns info displays the status of the DNS resolver. If DNS is not enabled, dns info will display a message to that effect. Otherwise dns info displays a list of all DNS servers configured in the resolv.conf file, whether the appliance believes the server to be operational, when the server was last polled, the average time in milliseconds for a DNS query, how many DNS queries were made, and how many queries resulted in errors. Following the list of servers is the appliance's default domain (i.e. a filer named toaster with a default domain of mycompany.com thinks its fully qualified name is toaster.mycompany.com) and a list of domains that are appended to unqualified names during lookup. Here is a sample output: 
  DNS is enabled

  DNS caching is enabled

  5 cache hits
  4 cache misses
  4 cache entries
  0 expired entries
  0 cache replacements

  IP Address       State Last Polled                  Avg RTT Calls  Errs
  -------------------------------------------------------------------------------
  172.19.2.30      UP    Mon Oct 22 20:30:05 PDT 2001       2    12     0
  172.19.3.32      ??                                       0     0     0

  Default domain: lab.mycompany.com
  Search domains: lab.mycompany.com mycompany.com
The first line of output indicates whether DNS is enabled (via the dns.enable option). If DNS is disabled, there will be no more output. The next line indicates whether DNS caching is enabled (via the dns.cache.enable option). If DNS caching is disabled, the next line of output will be the "IP Address..." heading. If DNS caching is enabled (as in the above example), the caching statistics will follow. The statistics cache hits and cache misses are the number of DNS requests that were found in the cache and the number which were not found and needed to issue a DNS request, respectively. The number of entries currently in the cache follows. Each cache miss inserts a new entry in the cache until the cache is full. Cache entries will expire and be discarded when they have reached the end of their Time To Live (TTL) as indicated by the DNS server. When the cache is full old entries will be replaced in a least recently used fashion. The table of DNS servers indicated the IP address, last known status, date of last DNS request, average round trip time (RTT) in milliseconds, number of requests, and number of errors reported per server. If a server has never been queried it will have a "??" in its status field. If the server responded to its last query it will have "UP" in in its status field, and if it never responded to the last query sent or had any other error condition it will have "DOWN" in its status field. Down servers will not be retried for 10 minutes. The default domain listed should be the same as the value of the dns.domainname option. The search domains are the domain suffixes used to convert unqualified domain names in fully qualified domain names (FQDNs). They are read from the search directive in /etc/resolv.conf. dns flush Removes all entries from the DNS cache. This command has no effect if the DNS cache is not enabled. All responses from a DNS server have a TTL (Time To Live) value associated with them. Cache entries will normally expire at the end of their time to live and a new value will be acquired from the DNS server. However if a DNS record changes before it has expired the DNS cache has no way of knowing that its information is up to date. In this case name resolutions on the filer will incorrectly return the old record and you must flush the DNS cache to force the filer to get the new DNS record. If some of your DNS records change very often you should make sure that your DNS server transmits them with a low TTL. You can also disable DNS caching on the filer via the dns.cache.enable option, but this may have an adverse performance impact.

VFILER CONSIDERATIONS

When run from a vfiler context, (e.g. via the vfiler run command), dns only reflects the concerned vfiler.

FILES

na_resolv.conf(5) Configures the DNS resolver

LIMITATIONS

The dns info command may list servers as DOWN when they are not in fact down, if the resolver has not polled the server since it came back up. If all DNS servers are down, dns info may list the last server in the list as UP when it is in fact down. This is because the DNS resolver will always try at least one server when trying to resolve a name, even if it has reason to believe that all servers are down.

SEE ALSO

na_nis(1), na_options(1), na_vfiler(1), na_dns(8)
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