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Top Forums UNIX for Advanced & Expert Users Interpretation of Ping behaviour Post 302921802 by jim mcnamara on Monday 20th of October 2014 11:21:34 AM
Old 10-20-2014
/etc/resolv.conf just enumerates the order and names of dns servers to check. You
may need to modify that. We use several dns servers in out network - two infoblox appliances and one windows domain controller.

As Made_in_Germany said, /etc/nsswitch.conf controls where to look in general.

Is your cache name service daemon running? Turn on dns caching.

Code:
/fmd> svcs /system/name-service-cache
STATE          STIME    FMRI
online         Oct_17   svc:/system/name-service-cache:default

Should say 'online'

Next check performance of the caching with
Code:
nscd -g

You want to see:
Code:
CACHE: hosts

         CONFIG:
         enabled: yes
         per user cache: no
         avoid name service: no
         check file: yes
         check file interval: 0
         positive ttl: 3600
         negative ttl: 5
         keep hot count: 20
         hint size: 2048
         max entries: 0 (unlimited)

         STATISTICS:
         positive hits: 39
         negative hits: 2
         positive misses: 2
         negative misses: 3
         total entries: 2
         queries queued: 0
         queries dropped: 0
         cache invalidations: 0
         cache hit rate:       89.1


CACHE: ipnodes

         CONFIG:
         enabled: yes
         per user cache: no
         avoid name service: no
         check file: yes
         check file interval: 0
         positive ttl: 3600
         negative ttl: 5
         keep hot count: 20
         hint size: 2048
         max entries: 0 (unlimited)

         STATISTICS:
         positive hits: 1104
         negative hits: 2
         positive misses: 25
         negative misses: 3
         total entries: 4
         queries queued: 0
         queries dropped: 0
         cache invalidations: 18
         cache hit rate:       97.5

You may need to increase your local dns cache size. Primarily what you need is a sysadmin/network admin who knows this stuff, and is not following a rote playbook for how to maintain a network.

The optimal solution for dns problems like this is most often to set up caching DNS servers, and turn off nscd.

As a side note, it is very slightly possible your cache is becoming stale, possibly a DNS server has problems. If the cache stuff is working you may want to bounce the nscd process. This will clear the caches. So if an immediate rerun of your problem continues, then you have other issues, which IMO tend to be nasty.

N.B.:
This kind of advice is hard to give without actually being there, too many moving parts to do a decent job vicariously like this.
 

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NSCD.CONF(5)							File Formats Manual						      NSCD.CONF(5)

NAME
nscd.conf - configuration file for Name Service Caching Daemon DESCRIPTION
/etc/nscd.conf configures the caches used by nscd(8) as well as some generic options. nscd(8) is able to use a configuration file at a different location, when supplied with the -f or --config-file command line option. The configuration file consists of a set of lines. Empty lines, and text after a '#' is ignored. All remaining lines denote the setting of an option. White space before and after options, and between options and option arguments is ignored. There are two kinds of options: General options influence nscd(8)'s general behaviour, while cache related options only affect the specified cache. Options are set like this: general_option option cache_option cache_name option GENERAL OPTIONS
logfile file Specifies the name of the debug log-file that nscd(8) should use if debug-level is higher than 0. If this option is not set, nscd(8) will write its debug output to stderr. debug-level level If level is higher than 0, nscd(8) will create some debug output. The higher the level, the more verbose the output. threads #threads This option sets the number of threads that nscd(8) should use by default. It can be overridden by calling nscd(8) with the -t or --nthreads argument. If neither this configuration option nor the command line argument is given, nscd(8) uses 5 threads by default. The minimum is 3. More threads means more simultaneous connections that nscd(8) can handle. max-threads #threads Specifies the maximum number of threads to be started. server-user user By default, nscd(8) is run as user root. This option can be set to force nscd(8) to drop root privileges after startup. It cannot be used when nscd(8) is called with the -S or --secure argument. Also note that some services require that nscd run as root, so using this may break those lookup services. stat-user user Specifies the user who is allowed to request statistics. paranoia bool bool must be one of yes or no. Enabling paranoia mode causes nscd(8) to restart itself periodically. restart-interval time Sets the restart interval to time seconds if periodic restart is enabled by enabling paranoia mode. The default value is 3600. CACHE OPTIONS
All cache options take two arguments. The first one denotes the service or cache the option should affect. Currently service can be one of passwd, group, or hosts. enable-cache service bool bool must be one of yes or no. Each cache is disabled by default and must be enabled explicitly by setting this options to yes. positive-time-to-live service secs This is the number of seconds after which a cached entry is removed from the cache. This defaults to 3600 seconds (i. e. one hour). negative-time-to-live service secs If an entry is not found by the Name Service, it is added to the cache and marked as "not existent". This option sets the number of seconds after which such a not existent entry is removed from the cache. This defaults to 20 seconds for the password and host caches and to 60 seconds for the group cache. suggested-size service prime-number This option sets the size of the hash that is used to store the cache entries. As this is a hash, it should be reasonably larger than the maximum number of entries that is expected to be cached simultaneously and should be a prime number. It defaults to a size of 211 entries. check-files service bool bool must be one of yes (default) or no. If file checking is enabled, nscd(8) periodically checks the modification time of /etc/passwd, /etc/group, or /etc/hosts (for the passwd, group, and host cache respectively) and invalidates the cache if the file has changed since the last check. persistent service bool bool must be one of yes (default) or no. Keep the content of the cache for service over nscd(8) restarts. Useful when paranoia mode is set. shared service bool bool must be one of yes (default) or no. The memory mapping of the nscd(8) databases for service is shared with the clients so that they can directly search in them instead of having to ask the daemon over the socket each time a lookup is performed. reload-count #number Sets the number of times a cached record is reloaded before it is pruned from the cache. Each cache record has a timeout, when that timeout expires, nscd(8) will either reload it (query the NSS service again if the data hasn't changed), or drop it. max-db-size service number-of-bytes Sets the maximum allowable size for the service. auto-propagate service bool When set to no for passwd or group service, then the .byname requests are not added to passwd.byuid or group.bygid cache. This may help for tables containing multiple records for the same id. EXAMPLE
# This is a comment. logfile /var/log/nscd.log threads 6 server-user nobody debug-level 0 enable-cache passwd yes positive-time-to-live passwd 600 negative-time-to-live passwd 20 suggested-size passwd 211 check-files passwd yes enable-cache group yes positive-time-to-live group 3600 negative-time-to-live group 60 suggested-size group 211 check-files group yes enable-cache hosts yes positive-time-to-live hosts 3600 negative-time-to-live hosts 20 suggested-size hosts 211 check-files hosts yes SEE ALSO
nscd(8), nsswitch.conf(5) 4.2 Berkeley Distribution 07 January 2001 NSCD.CONF(5)
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