error: socket.c:1540: unexpected error:

We have upgraded from 9.11.19 to 9.16.3 overnight and have now started to see these events in the syslog.

Jun  9 22:20:13 pad-res0 named[58819]: error: socket.c:1540: unexpected error:
Jun  9 22:20:13 pad-res0 named[58819]: error: unable to convert errno to isc_result: 71: Protocol error

After restart last night:

Jun  9 16:14:34 pad-res0 named[58819]: starting BIND 9.16.3 (Stable Release) <id:5ea41c1>
Jun  9 16:14:34 pad-res0 named[58819]: running on Linux x86_64 2.6.32-754.17.1.el6.x86_64 #1 SMP Thu Jun 20 11:47:12 EDT 2019
Jun  9 16:14:34 pad-res0 named[58819]: built with '--prefix=/usr/local/' '--sysconfdir=/etc' '--with-python=no' '--with-json-c' 'PKG_CONFIG_PATH=:/usr/local/lib/pkgconfig:/usr/lib64/pkgconfig:/usr/share/pkgconfig'
Jun  9 16:14:34 pad-res0 named[58819]: running as: named -f -u named
Jun  9 16:14:34 pad-res0 named[58819]: compiled by GCC 4.4.7 20120313 (Red Hat 4.4.7-23)
Jun  9 16:14:34 pad-res0 named[58819]: compiled with OpenSSL version: OpenSSL 1.0.1e-fips 11 Feb 2013
Jun  9 16:14:34 pad-res0 named[58819]: linked to OpenSSL version: OpenSSL 1.0.1e-fips 11 Feb 2013
Jun  9 16:14:34 pad-res0 named[58819]: compiled with libxml2 version: 2.7.6
Jun  9 16:14:34 pad-res0 named[58819]: linked to libxml2 version: 20706
Jun  9 16:14:34 pad-res0 named[58819]: compiled with json-c version: 0.11
Jun  9 16:14:34 pad-res0 named[58819]: linked to json-c version: 0.11
Jun  9 16:14:34 pad-res0 named[58819]: compiled with zlib version: 1.2.3
Jun  9 16:14:34 pad-res0 named[58819]: linked to zlib version: 1.2.3
Jun  9 16:14:34 pad-res0 named[58819]: ----------------------------------------------------
Jun  9 16:14:34 pad-res0 named[58819]: BIND 9 is maintained by Internet Systems Consortium,
Jun  9 16:14:34 pad-res0 named[58819]: Inc. (ISC), a non-profit 501(c)(3) public-benefit
Jun  9 16:14:34 pad-res0 named[58819]: corporation.  Support and training for BIND 9 are
Jun  9 16:14:34 pad-res0 named[58819]: available at https://www.isc.org/support
Jun  9 16:14:34 pad-res0 named[58819]: ----------------------------------------------------
Jun  9 16:14:34 pad-res0 named[58819]: adjusted limit on open files from 4096 to 1048576
Jun  9 16:14:34 pad-res0 named[58819]: /etc/named.conf:27: option 'dnssec-enable' is obsolete and should be removed
Jun  9 16:14:34 pad-res0 named[58819]: couldn't mkdir '/usr/local/var/run/named': Permission denied
Jun  9 16:14:34 pad-res0 named[58819]: couldn't mkdir '/usr/local/var/run/named': Permission denied
Jun  9 16:14:34 pad-res0 named[58819]: could not create /usr/local/var/run/named/session.key
Jun  9 16:14:34 pad-res0 named[58819]: failed to generate session key for dynamic DNS: permission denied
Jun  9 16:14:34 pad-res0 named[58819]: command channel listening on 127.0.0.1#953
Jun  9 16:14:34 pad-res0 named[58819]: command channel listening on ::1#953
Jun  9 16:14:34 pad-res0 named[58819]: notice: all zones loaded
Jun  9 16:14:34 pad-res0 named[58819]: notice: running
Jun  9 16:14:34 pad-res0 named[58819]: warning: checkhints: view defaultview: b.root-servers.net/A (199.9.14.201) missing from hints
Jun  9 16:14:34 pad-res0 named[58819]: warning: checkhints: view defaultview: b.root-servers.net/A (192.228.79.201) extra record in hints
Jun  9 16:14:34 pad-res0 named[58819]: warning: checkhints: view defaultview: b.root-servers.net/AAAA (2001:500:200::b) missing from hints
Jun  9 16:14:34 pad-res0 named[58819]: warning: checkhints: view defaultview: b.root-servers.net/AAAA (2001:500:84::b) extra record in hints
Jun  9 16:22:35 pad-res0 named[58819]: error: socket.c:1540: unexpected error:
Jun  9 16:22:35 pad-res0 named[58819]: error: unable to convert errno to isc_result: 71: Protocol error
Jun  9 16:22:35 pad-res0 named[58819]: error: socket.c:1540: unexpected error:
Jun  9 16:22:35 pad-res0 named[58819]: error: unable to convert errno to isc_result: 71: Protocol error
Jun  9 17:01:02 pad-res0 ntpdate[17116]: adjust time server 203.14.0.251 offset 0.047735 sec
Jun  9 17:13:02 pad-res0 named[58819]: error: socket.c:1540: unexpected error:
Jun  9 17:13:02 pad-res0 named[58819]: error: unable to convert errno to isc_result: 71: Protocol error
Jun  9 17:13:02 pad-res0 named[58819]: error: socket.c:1540: unexpected error:
Jun  9 17:13:02 pad-res0 named[58819]: error: unable to convert errno to isc_result: 71: Protocol error
Jun  9 17:28:28 pad-res0 named[58819]: error: socket.c:1540: unexpected error:

We are unsure what the error is relating to. Happy to provide any logs you require as these events are being recorded reasonably often.

RT #16586