Bind suddenly starts responding clients with servfail

Frey, Rick E Rick.Frey at
Mon Apr 27 13:11:56 UTC 2020

Recursive clients are lookups/clients on your nameserver on behalf of a query received.  If you are seeing that your nameserver is running out of recursive clients after removing “all” traffic, it would indicate something is still querying your nameserver as BIND won’t spontaneously create recursive lookups.  Perhaps something local on the server is generating queries?

A dump of existing recursive clients can be performed using “rndc recursing”.   Output is normally “named.recursing” in your data directory.

I would suspect that your server may be unable to make outbound connections to authoritative servers.  This could cause high number of recursive clients.  Note that behavior of BIND is to start dropping older outstanding recursive lookups once 90% of recursive clients is reached (900 recursive clients in your case).  Thus, a high number of recursive clients in itself normally doesn’t result in SERVFAIL for queries.

Not sure why you’re unable to run rndc commands (local or remote?).   Perhaps you are out of file descriptors as well?

From: bind-users <bind-users-bounces at> on behalf of Søren Andersen <SOAN at>
Date: Monday, April 27, 2020 at 4:00 AM
To: "bind-users at" <bind-users at>
Subject: Bind suddenly starts responding clients with servfail

Hello List,

I'm running a few BIND servers, but lately one of my servers suddenly starts responding to clients with servfail for every request from the clients, and BIND doesn't respond to the rndc or statistics interface anymore.

My logs for client-channel show me this:
25-Apr-2020 21:52:04.501 client @XX XX.37#2921 (<>): no more recursive clients (1000/900/1000): quota reached

I've removed all the dns traffic from the server, and the quota is still reached after 6+ hours?

Do you guys have some clue what all this is about? - Or any suggestions where to look for any further information?

I'm running BIND 9.16.1 on CentOS 7:

named -V
BIND 9.16.1 (Stable Release) <id:d497c32>
running on Linux x86_64 3.10.0-1062.el7.x86_64 #1 SMP Wed Aug 7 18:08:02 UTC 2019
built by make with '--build=x86_64-redhat-linux-gnu' '--host=x86_64-redhat-linux-gnu' '--program-prefix=' '--disable-dependency-tracking' '--prefix=/opt/isc/isc-bind/root/usr' '--exec-prefix=/opt/isc/isc-bind/root/usr' '--bindir=/opt/isc/isc-bind/root/usr/bin' '--sbindir=/opt/isc/isc-bind/root/usr/sbin' '--sysconfdir=/etc/opt/isc/isc-bind' '--datadir=/opt/isc/isc-bind/root/usr/share' '--includedir=/opt/isc/isc-bind/root/usr/include' '--libdir=/opt/isc/isc-bind/root/usr/lib64' '--libexecdir=/opt/isc/isc-bind/root/usr/libexec' '--localstatedir=/var/opt/isc/isc-bind' '--sharedstatedir=/var/opt/isc/isc-bind/lib' '--mandir=/opt/isc/isc-bind/root/usr/share/man' '--infodir=/opt/isc/isc-bind/root/usr/share/info' '--disable-static' '--enable-dnstap' '--with-pic' '--with-gssapi' '--with-json-c' '--with-libtool' '--with-libxml2' '--without-lmdb' '--with-docbook-xsl=/usr/share/sgml/docbook/xsl-stylesheets' '--with-python' 'build_alias=x86_64-redhat-linux-gnu' 'host_alias=x86_64-redhat-linux-gnu' 'CFLAGS=-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic' 'LDFLAGS= -L/opt/isc/isc-bind/root/usr/lib64' 'PKG_CONFIG_PATH=:/opt/isc/isc-bind/root/usr/lib64/pkgconfig:/opt/isc/isc-bind/root/usr/share/pkgconfig'
compiled by GCC 4.8.5 20150623 (Red Hat 4.8.5-39)
compiled with OpenSSL version: OpenSSL 1.0.2k-fips  26 Jan 2017
linked to OpenSSL version: OpenSSL 1.0.2k-fips  26 Jan 2017
compiled with libxml2 version: 2.9.1
linked to libxml2 version: 20901
compiled with json-c version: 0.11
linked to json-c version: 0.11
compiled with zlib version: 1.2.7
linked to zlib version: 1.2.7
compiled with protobuf-c version: 1.3.2
linked to protobuf-c version: 1.3.2
threads support is enabled

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