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Full Discussion: Interpretation of Ping behaviour
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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LEARN ABOUT DEBIAN

desproxy-dns

desproxy-dns(1) 						   User Commands						   desproxy-dns(1)

NAME

       desproxy-dns - DNS for dynamic connections

SYNOPSIS

	  desproxy-dns dns_server proxy_host proxy_port

OPTIONS

       None

DESCRIPTION

       If you have direct DNS access then you don't need to do anything else.  You know you have direct DNS access if you can resolve host names
       to IP addresses.

       NOTE: as desproxy-dns listens in port 53 (which is less than 1024) you may need administrator privileges to exec desproxy-dns (in fact if
       you are running UN*X, you actually have to run desproxy-dns as root).

       OK, so you have a dns server accessible now. But your computer doesn't know anything about that. You must configure your network
       accordingly (again, need to be root in UN*X).

       Edit /etc/resolv.conf and add the line "nameserver 127.0.0.1". You don't have to restart anything. Just test ping and see if it works.

ENVIRONMENT

       None.

FILES

       None.

SEE ALSO

       dnsproxy(1), ping(1)

AUTHORS

       This manual page was written by Jari Aalto <jari.aalto@cante.net>, for the Debian GNU system (but may be used by others). Released under
       license GPL v2 or any later version.

desproxy-dns							    2012-03-26							   desproxy-dns(1)
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