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Top Forums UNIX for Advanced & Expert Users One of the two DNS server going down causes impacts Post 303043094 by Peasant on Saturday 18th of January 2020 02:07:05 AM
Old 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.
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DNSPROXY(1)						    BSD General Commands Manual 					       DNSPROXY(1)

NAME
dnsproxy -- DNS proxy SYNOPSIS
dnsproxy [-dhV] [-c file] DESCRIPTION
The dnsproxy daemon waits for nameserver queries on a user specified address, dispatches these queries to authoritative and recursive name- servers and forwards the received answers back to the original client. The options are as follows: -c file Read configuration from file. -d Detach from current terminal and run as background process. -h Show usage. -V Show version. If a client from an internal IP address does a recursive lookup the query is forwarded to a recursive DNS server. Authoritative queries and queries coming from clients in foreign networks are forwarded to an authoritative DNS server. CONFIGURATION FILE
At startup dnsproxy reads a configuration file specified via the -c option or at the default location of /etc/dnsproxy.conf. The following keywords are recognized: authoritative IP Address of the authoritative nameserver [required]. recursive IP Address of the recursive nameserver [required]. listen IP Local address (defaults to 0.0.0.0). port number Local port number (defaults to 53). chroot path A path to chroot to before starting to answer queries. user name A user to change to before starting to answer queries. authoritative-timeout seconds Time in seconds when authoritative queries time out (defaults to 10). recursive-timeout seconds Time in seconds when recursive queries time out (defaults to 90). authoritative-port number Port number on authoritative nameserver (defaults to 53). recursive-port number Port number on recursive nameserver (defaults to 53). statistics seconds Period between output of statistics (defaults to 3600). Use 0 to disable output of statistics completely. internal network Declare networks recognized as internal and thus eligible to do recursive queries. One network in CIDR notation per keyword. EXAMPLE authoritative 10.1.1.1 recursive 127.0.0.1 recursive-port 10053 listen 192.168.1.1 port 53 chroot /var/empty user nobody internal 192.168.1.0/24 internal 127.0.0.1 STATISTICS
Every hour (by default) dnsproxy logs the collected statistics about its usage to standard error (or syslog when running detached). Statis- tics look like ActiveQr AuthorQr RecursQr AllQuery Answered 0 0 0 0 0 TimeoutQ DroppedQ DroppedA LateAnsw HashColl 0 0 0 0 0 and have the following meaning: ActiveQr Number of currently active queries proxied to the servers. AuthorQr Accumulated number of authoritative queries. RecursQr Accumulated number of recursive queries. AllQuery Accumulated number of all queries ever received. Answered Accumulated number of answered queries. TimeoutQ Accumulated number of queries that did not receive an answer in time. DroppedQ Accumulated number of dropped queries (e.g. transmission errors). DroppedA Accumulated number of dropped answers. LateAnsw Accumulated number of answers received after the timeout period. HashColl Accumulated number of hash collisions in the query list. SEE ALSO
named(1) VERSION
This manual page describes dnsproxy version 1.16. AUTHORS
Armin Wolfermann <armin@wolfermann.org> The dnsproxy homepage is at http://www.wolfermann.org/dnsproxy.html. LOCAL
November 29, 2003 LOCAL
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