01-18-2020
I've seen this mostly related to DNS query timeouts setup from client side.
The defaults are quite high on most linux/unix operating system, from AIX man page online :
Quote:
timeout:n Enables you to specify the initial timeout for a query to a nameserver. The default value is five seconds. The maximum value is 30 seconds. For the second and successive rounds of queries, the resolver doubles the initial timeout and is divided by the number of nameservers in the resolv.conf file.
attempts:n Enables you to specify how many queries the resolver should send to each nameserver in the resolv.conf file before it stops execution. The default value is 4. The maximum value is 5.
In practice if you have, for instance, two dns servers, and first one
/etc/resolv.conf goes down...
The system will try to query first with timeout of 5 seconds and 4 attempts, totaling 20 seconds, until second is tried.
This will for sure hit some timeouts from application side, e.g application will timeout before system returns valid DNS entry.
As for
nslookup working, i'm unsure. It this from the same box ?
Suggestion is to change to defaults to lower values and/or implement DNS caching mechanism locally on AIX box.
Hope that helps
Regards
Peasant.
These 2 Users Gave Thanks to Peasant For This Post:
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LEARN ABOUT ULTRIX
resolv.conf
resolv.conf(5) File Formats Manual resolv.conf(5)
Name
resolv.conf - resolver configuration file
Description
The resolver configuration file, contains information that the resolver routines read the first time they are invoked by a process. The
resolver file contains ASCII text and lists the name-value pairs that provide various types of resolver information.
The file is required if your system is running BIND. This file must contain the BIND domain name for the local area network. If your sys-
tem is a BIND client, this file must also contain nameserver entries.
There are two entry formats for the file:
domain binddomain
This line specifies the default domain to append to local host names. If no domain entries are present, the domain returned by
after the first dot (.) is used. If the host name does not contain a domain, the root domain is assumed.
nameserver address
In this entry, the address is the IP address, in dot notation, of the BIND server that should be queried to resolve host name and
address information. You should have at least one name server listed. Two or more name servers reduces the possibility of inter-
rupted BIND service in the event that one of the servers is down. You can list up to (10) name servers. If more than one server is
listed, the resolver library queries you to try them in the order listed. If no name server entries are present, the default is to
use the name server on the local machine.
The algorithm used is to try a name server, and, if the query times out, to try the next, until out of name servers or the query is
resolved. The last step is to repeat trying all the name servers until a maximum number of retries has been made or the query has
been resolved.
The name value pair must appear on a single line, and the keyword or must start each line.
Examples
The following is an example of a file:
;
; Data file for a client
;
domain cities.us
nameserver 128.11.22.33
Lines beginning with a semicolon (;) are comment lines.
Files
See Also
gethostname(2), resolver(3), named(8)
Guide to the BIND Service
resolv.conf(5)