Release Notes


BIND 9.16 (Extended Support Version) is a stable branch of BIND. This document summarizes significant changes since the last production release on that branch. Please see the CHANGES file for a more detailed list of changes and bug fixes.

Note on Version Numbering

As of BIND 9.13/9.14, BIND has adopted the “odd-unstable/even-stable” release numbering convention. BIND 9.16 contains new features that were added during the BIND 9.15 development process. Henceforth, the 9.16 branch will be limited to bug fixes, and new feature development will proceed in the unstable 9.17 branch.

Supported Platforms

To build on Unix-like systems, BIND requires support for POSIX.1c threads (IEEE Std 1003.1c-1995), the Advanced Sockets API for IPv6 (RFC 3542), and standard atomic operations provided by the C compiler.

The libuv asynchronous I/O library and the OpenSSL cryptography library must be available for the target platform. A PKCS#11 provider can be used instead of OpenSSL for Public Key cryptography (i.e., DNSSEC signing and validation), but OpenSSL is still required for general cryptography operations such as hashing and random number generation.

More information can be found in the file that is included in the source distribution of BIND 9. If your compiler and system libraries provide the above features, BIND 9 should compile and run. If that is not the case, the BIND development team will generally accept patches that add support for systems that are still supported by their respective vendors.


The latest versions of BIND 9 software can always be found at There you will find additional information about each release, source code, and pre-compiled versions for Microsoft Windows operating systems.

Notes for BIND 9.16.21

New Features

  • Support for HTTPS and SVCB record types has been added. (This does not include ADDITIONAL section processing for these record types, only basic support for RR type parsing and printing.) [GL #1132]

Feature Changes

  • When dnssec-signzone signs a zone using a successor key whose predecessor is still published, it now only refreshes signatures for RRsets which have an invalid signature, an expired signature, or a signature which expires within the provided cycle interval. This allows dnssec-signzone to gradually replace signatures in a zone whose ZSK is being rolled over (similarly to what auto-dnssec maintain; does). [GL #1551]

Bug Fixes

  • A recent change to the internal memory structure of zone databases inadvertently neglected to update the MAPAPI value for zone files in map format. This caused version 9.16.20 of named to attempt to load files into memory that were no longer compatible, triggering an assertion failure on startup. The MAPAPI value has now been updated, so named rejects outdated files when encountering them. [GL #2872]

  • Zone files in map format whose size exceeded 2 GB failed to load. This has been fixed. [GL #2878]

  • named was unable to run as a Windows Service under certain circumstances. This has been fixed. [GL #2837]

  • Stale data in the cache could cause named to send non-minimized queries despite QNAME minimization being enabled. This has been fixed. [GL #2665]

  • When a DNSSEC-signed zone which only has a single signing key available is migrated to dnssec-policy, that key is now treated as a Combined Signing Key (CSK). [GL #2857]

  • When a dynamic zone was made available in another view using the in-view statement, running rndc freeze always reported an already frozen error even though the zone was successfully frozen. This has been fixed. [GL #2844]

Notes for BIND 9.16.20

Security Fixes

  • Fixed an assertion failure that occurred in named when it attempted to send a UDP packet that exceeded the MTU size, if Response Rate Limiting (RRL) was enabled. (CVE-2021-25218) [GL #2856]

  • named failed to check the opcode of responses when performing zone refreshes, stub zone updates, and UPDATE forwarding. This could lead to an assertion failure under certain conditions and has been addressed by rejecting responses whose opcode does not match the expected value. [GL #2762]

Feature Changes

  • Testing revealed that setting the thread affinity for various types of named threads led to inconsistent recursive performance, as sometimes multiple sets of threads competed over a single resource.

    Due to the above, named no longer sets thread affinity. This causes a slight dip of around 5% in authoritative performance, but recursive performance is now consistently improved. [GL #2822]

  • CDS and CDNSKEY records can now be published in a zone without the requirement that they exactly match an existing DNSKEY record, as long as the zone is signed with an algorithm represented in the CDS or CDNSKEY record. This allows a clean rollover from one DNS provider to another when using a multiple-signer DNSSEC configuration. [GL #2710]

Bug Fixes

  • Authentication of rndc messages could fail if a controls statement was configured with multiple key algorithms for the same listener. This has been fixed. [GL #2756]

Notes for BIND 9.16.19

New Features

  • Using a new configuration option, parental-agents, each zone can now be associated with a list of servers that can be used to check the DS RRset in the parent zone. This enables automatic KSK rollovers. [GL #1126]

Feature Changes

  • IP fragmentation has been disabled for outgoing UDP sockets. Errors triggered by sending DNS messages larger than the specified path MTU are properly handled by sending empty DNS replies with the TC (TrunCated) bit set, which forces DNS clients to fall back to TCP. [GL #2790]

Bug Fixes

  • The code managing RFC 5011 trust anchors created an invalid placeholder keydata record upon a refresh failure, which prevented the database of managed keys from subsequently being read back. This has been fixed. [GL #2686]

  • Signed, insecure delegation responses prepared by named either lacked the necessary NSEC records or contained duplicate NSEC records when both wildcard expansion and CNAME chaining were required to prepare the response. This has been fixed. [GL #2759]

  • If nsupdate sends an SOA request and receives a REFUSED response, it now fails over to the next available server. [GL #2758]

  • A bug that caused the NSEC3 salt to be changed on every restart for zones using KASP has been fixed. [GL #2725]

  • The configuration-checking code failed to account for the inheritance rules of the dnssec-policy option. This has been fixed. [GL #2780]

  • The fix for [GL #1875] inadvertently introduced a deadlock: when locking key files for reading and writing, the in-view logic was not considered. This has been fixed. [GL #2783]

  • A race condition could occur where two threads were competing for the same set of key file locks, leading to a deadlock. This has been fixed. [GL #2786]

Notes for BIND 9.16.18

Bug Fixes

  • When preparing DNS responses, named could replace the letters W (uppercase) and w (lowercase) with \000. This has been fixed. [GL #2779]

  • The configuration-checking code failed to account for the inheritance rules of the key-directory option. As a side effect of this flaw, the code detecting key-directory conflicts for zones using KASP incorrectly reported unique key directories as being reused. This has been fixed. [GL #2778]

Notes for BIND 9.16.17

Feature Changes

  • After the network manager was introduced to named to handle incoming traffic, it was discovered that recursive performance had degraded compared to previous BIND 9 versions. This has now been fixed by processing internal tasks inside network manager worker threads, preventing resource contention among two sets of threads. [GL #2638]

  • Zone dumping tasks are now run on separate asynchronous thread pools. This change prevents zone dumping from blocking network I/O. [GL #2732]

  • inline-signing was incorrectly described as being inherited from the options/view levels and was incorrectly accepted at those levels without effect. This has been fixed; named.conf files with inline-signing at those levels no longer load. [GL #2536]

Bug Fixes

  • The calculation of the estimated IXFR transaction size in dns_journal_iter_init() was invalid. This resulted in excessive AXFR-style IXFR responses. [GL #2685]

  • Fixed an assertion failure that could occur if stale data was used to answer a query, and then a prefetch was triggered after the query was restarted (for example, to follow a CNAME). [GL #2733]

  • If a query was answered with stale data on a server with DNS64 enabled, an assertion could occur if a non-stale answer arrived afterward. This has been fixed. [GL #2731]

  • Fixed an error which caused the IP_DONTFRAG socket option to be enabled instead of disabled, leading to errors when sending oversized UDP packets. [GL #2746]

  • Zones which are configured in multiple views, with different values set for dnssec-policy and with identical values set for key-directory, are now detected and treated as a configuration error. [GL #2463]

  • A race condition could occur when reading and writing key files for zones using KASP and configured in multiple views. This has been fixed. [GL #1875]

Notes for BIND 9.16.16

Feature Changes

  • DNSSEC responses containing NSEC3 records with iteration counts greater than 150 are now treated as insecure. [GL #2445]

  • The maximum supported number of NSEC3 iterations that can be configured for a zone has been reduced to 150. [GL #2642]

  • The default value of the max-ixfr-ratio option was changed to unlimited, for better backwards compatibility in the stable release series. [GL #2671]

  • Zones that want to transition from secure to insecure mode without becoming bogus in the process must now have their dnssec-policy changed first to insecure, rather than none. After the DNSSEC records have been removed from the zone, the dnssec-policy can be set to none or removed from the configuration. Setting the dnssec-policy to insecure causes CDS and CDNSKEY DELETE records to be published. [GL #2645]

  • The implementation of the ZONEMD RR type has been updated to match RFC 8976. [GL #2658]

  • The draft-vandijk-dnsop-nsec-ttl IETF draft was implemented: NSEC(3) TTL values are now set to the minimum of the SOA MINIMUM value or the SOA TTL. [GL #2347]

Bug Fixes

  • It was possible for corrupt journal files generated by an earlier version of named to cause problems after an upgrade. This has been fixed. [GL #2670]

  • TTL values in cache dumps were reported incorrectly when stale-cache-enable was set to yes. This has been fixed. [GL #389] [GL #2289]

  • A deadlock could occur when multiple rndc addzone, rndc delzone, and/or rndc modzone commands were invoked simultaneously for different zones. This has been fixed. [GL #2626]

  • named and named-checkconf did not report an error when multiple zones with the dnssec-policy option set were using the same zone file. This has been fixed. [GL #2603]

  • If dnssec-policy was active and a private key file was temporarily offline during a rekey event, named could incorrectly introduce replacement keys and break a signed zone. This has been fixed. [GL #2596]

  • When generating zone signing keys, KASP now also checks for key ID conflicts among newly created keys, rather than just between new and existing ones. [GL #2628]

Notes for BIND 9.16.15

Security Fixes

  • A malformed incoming IXFR transfer could trigger an assertion failure in named, causing it to quit abnormally. (CVE-2021-25214)

    ISC would like to thank Greg Kuechle of SaskTel for bringing this vulnerability to our attention. [GL #2467]

  • named crashed when a DNAME record placed in the ANSWER section during DNAME chasing turned out to be the final answer to a client query. (CVE-2021-25215)

    ISC would like to thank Siva Kakarla for bringing this vulnerability to our attention. [GL #2540]

  • When a server’s configuration set the tkey-gssapi-keytab or tkey-gssapi-credential option, a specially crafted GSS-TSIG query could cause a buffer overflow in the ISC implementation of SPNEGO (a protocol enabling negotiation of the security mechanism used for GSSAPI authentication). This flaw could be exploited to crash named binaries compiled for 64-bit platforms, and could enable remote code execution when named was compiled for 32-bit platforms. (CVE-2021-25216)

    This vulnerability was reported to us as ZDI-CAN-13347 by Trend Micro Zero Day Initiative. [GL #2604]

Feature Changes

  • The ISC implementation of SPNEGO was removed from BIND 9 source code. Instead, BIND 9 now always uses the SPNEGO implementation provided by the system GSSAPI library when it is built with GSSAPI support. All major contemporary Kerberos/GSSAPI libraries contain an implementation of the SPNEGO mechanism. [GL #2607]

  • The default value for the stale-answer-client-timeout option was changed from 1800 (ms) to off. The default value may be changed again in future releases as this feature matures. [GL #2608]

Bug Fixes

  • TCP idle and initial timeouts were being incorrectly applied: only the tcp-initial-timeout was applied on the whole connection, even if the connection were still active, which could prevent a large zone transfer from being sent back to the client. The default setting for tcp-initial-timeout was 30 seconds, which meant that any TCP connection taking more than 30 seconds was abruptly terminated. This has been fixed. [GL #2583]

  • When stale-answer-client-timeout was set to a positive value and recursion for a client query completed when named was about to look for a stale answer, an assertion could fail in query_respond(), resulting in a crash. This has been fixed. [GL #2594]

  • If zone journal files written by BIND 9.16.11 or earlier were present when BIND was upgraded to BIND 9.16.13 or BIND 9.16.14, the zone file for that zone could have been inadvertently rewritten with the current zone contents. This caused the original zone file structure (e.g. comments, $INCLUDE directives) to be lost, although the zone data itself was preserved. [GL #2623]

  • After upgrading to BIND 9.16.13, journal files for trust anchor databases (e.g. managed-keys.bind.jnl) could be left in a corrupt state. (Other zone journal files were not affected.) This has been fixed. If a corrupt journal file is detected, named can now recover from it. [GL #2600]

  • When sending queries over TCP, dig now properly handles +tries=1 +retry=0 by not retrying the connection when the remote server closes the connection prematurely. [GL #2490]

  • CDS/CDNSKEY DELETE records are now removed when a zone transitions from a secure to an insecure state. named-checkzone also no longer reports an error when such records are found in an unsigned zone. [GL #2517]

  • Zones using KASP could not be thawed after they were frozen using rndc freeze. This has been fixed. [GL #2523]

  • After rndc checkds -checkds or rndc dnssec -rollover is used, named now immediately attempts to reconfigure zone keys. This change prevents unnecessary key rollover delays. [GL #2488]

  • Previously, a memory leak could occur when named failed to bind a UDP socket to a network interface. This has been fixed. [GL #2575]

Notes for BIND 9.16.14


The BIND 9.16.14 release was withdrawn after a backporting bug was discovered during pre-release testing. ISC would like to acknowledge the assistance of Natan Segal of Bluecat Networks.

Notes for BIND 9.16.13

New Features

  • A new purge-keys option has been added to dnssec-policy. It sets the period of time that key files are retained after becoming obsolete due to a key rollover; the default is 90 days. This feature can be disabled by setting purge-keys to 0. [GL #2408]

Feature Changes

  • When serve-stale is enabled and stale data is available, named now returns stale answers upon encountering any unexpected error in the query resolution process. This may happen, for example, if the fetches-per-server or fetches-per-zone limits are reached. In this case, named attempts to answer DNS requests with stale data, but does not start the stale-refresh-time window. [GL #2434]

Bug Fixes

  • Zone journal (.jnl) files created by versions of named prior to 9.16.12 were no longer compatible; this could cause problems when upgrading if journal files were not synchronized first. This has been corrected: older journal files can now be read when starting up. When an old-style journal file is detected, it is updated to the new format immediately after loading.

    Note that journals created by the current version of named are not usable by versions prior to 9.16.12. Before downgrading to a prior release, users are advised to ensure that all dynamic zones have been synchronized using rndc sync -clean.

    A journal file’s format can be changed manually by running named-journalprint -d (downgrade) or named-journalprint -u (upgrade). Note that this must not be done while named is running. [GL #2505]

  • named crashed when it was allowed to serve stale answers and stale-answer-client-timeout was triggered without any (stale) data available in the cache to answer the query. [GL #2503]

  • If an outgoing packet exceeded max-udp-size, named dropped it instead of sending back a proper response. To prevent this problem, the IP_DONTFRAG option is no longer set on UDP sockets, which has been happening since BIND 9.16.11. [GL #2466]

  • NSEC3 records were not immediately created when signing a dynamic zone using dnssec-policy with nsec3param. This has been fixed. [GL #2498]

  • A memory leak occurred when named was reconfigured after adding an inline-signed zone with auto-dnssec maintain enabled. This has been fixed. [GL #2041]

  • An invalid direction field (not one of N, S, E, W) in a LOC record resulted in an INSIST failure when a zone file containing such a record was loaded. [GL #2499]

Notes for BIND 9.16.12

Security Fixes

  • When tkey-gssapi-keytab or tkey-gssapi-credential was configured, a specially crafted GSS-TSIG query could cause a buffer overflow in the ISC implementation of SPNEGO (a protocol enabling negotiation of the security mechanism to use for GSSAPI authentication). This flaw could be exploited to crash named. Theoretically, it also enabled remote code execution, but achieving the latter is very difficult in real-world conditions. (CVE-2020-8625)

    This vulnerability was responsibly reported to us as ZDI-CAN-12302 by Trend Micro Zero Day Initiative. [GL #2354]

New Features

  • When a secondary server receives a large incremental zone transfer (IXFR), it can have a negative impact on query performance while the incremental changes are applied to the zone. To address this, named can now limit the size of IXFR responses it sends in response to zone transfer requests. If an IXFR response would be larger than an AXFR of the entire zone, it will send an AXFR response instead.

    This behavior is controlled by the max-ixfr-ratio option - a percentage value representing the ratio of IXFR size to the size of a full zone transfer. The default is 100%. [GL #1515]

  • A new option, stale-answer-client-timeout, has been added to improve named’s behavior with respect to serving stale data. The option defines the amount of time named waits before attempting to answer the query with a stale RRset from cache. If a stale answer is found, named continues the ongoing fetches, attempting to refresh the RRset in cache until the resolver-query-timeout interval is reached.

    The default value is 1800 (in milliseconds) and the maximum value is limited to resolver-query-timeout minus one second. A value of 0 causes any available cached RRset to immediately be returned while still triggering a refresh of the data in cache.

    This new behavior can be disabled by setting stale-answer-client-timeout to off or disabled. The new option has no effect if stale-answer-enable is disabled. [GL #2247]

Feature Changes

  • As part of an ongoing effort to use RFC 8499 terminology, primaries can now be used as a synonym for masters in named.conf. Similarly, notify primary-only can now be used as a synonym for notify master-only. The output of rndc zonestatus now uses primary and secondary terminology. [GL #1948]

  • The default value of max-stale-ttl has been changed from 12 hours to 1 day and the default value of stale-answer-ttl has been changed from 1 second to 30 seconds, following RFC 8767 recommendations. [GL #2248]

  • The SONAMEs for BIND 9 libraries now include the current BIND 9 version number, in an effort to tightly couple internal libraries with a specific release. This change makes the BIND 9 release process both simpler and more consistent while also unequivocally preventing BIND 9 binaries from silently loading wrong versions of shared libraries (or multiple versions of the same shared library) at startup. [GL #2387]

  • When check-names is in effect, A records below an _spf, _spf_rate, or _spf_verify label (which are employed by the exists SPF mechanism defined in RFC 7208 section 5.7/appendix D.1) are no longer reported as warnings/errors. [GL #2377]

Bug Fixes

  • named failed to start when its configuration included a zone with a non-builtin allow-update ACL attached. [GL #2413]

  • Previously, dnssec-keyfromlabel crashed when operating on an ECDSA key. This has been fixed. [GL #2178]

  • KASP incorrectly set signature validity to the value of the DNSKEY signature validity. This has been fixed. [GL #2383]

  • When migrating to KASP, BIND 9 considered keys with the Inactive and/or Delete timing metadata to be possible active keys. This has been fixed. [GL #2406]

  • Fix the “three is a crowd” key rollover bug in KASP. When keys rolled faster than the time required to finish the rollover procedure, the successor relation equation failed because it assumed only two keys were taking part in a rollover. This could lead to premature removal of predecessor keys. BIND 9 now implements a recursive successor relation, as described in the paper “Flexible and Robust Key Rollover” (Equation (2)). [GL #2375]

  • Performance of the DNSSEC verification code (used by dnssec-signzone, dnssec-verify, and mirror zones) has been improved. [GL #2073]

Notes for BIND 9.16.11

Feature Changes

  • The new networking code introduced in BIND 9.16 (netmgr) was overhauled in order to make it more stable, testable, and maintainable. [GL #2321]

  • Earlier releases of BIND versions 9.16 and newer required the operating system to support load-balanced sockets in order for named to be able to achieve high performance (by distributing incoming queries among multiple threads). However, the only operating systems currently known to support load-balanced sockets are Linux and FreeBSD 12, which means both UDP and TCP performance were limited to a single thread on other systems. As of BIND 9.16.11, named attempts to distribute incoming queries among multiple threads on systems which lack support for load-balanced sockets (except Windows). [GL #2137]

  • It is now possible to transition a zone from secure to insecure mode without making it bogus in the process; changing to dnssec-policy none; also causes CDS and CDNSKEY DELETE records to be published, to signal that the entire DS RRset at the parent must be removed, as described in RFC 8078. [GL #1750]

  • When using the unixtime or date method to update the SOA serial number, named and dnssec-signzone silently fell back to the increment method to prevent the new serial number from being smaller than the old serial number (using serial number arithmetics). dnssec-signzone now prints a warning message, and named logs a warning, when such a fallback happens. [GL #2058]

Bug Fixes

  • Multiple threads could attempt to destroy a single RBTDB instance at the same time, resulting in an unpredictable but low-probability assertion failure in free_rbtdb(). This has been fixed. [GL #2317]

  • named no longer attempts to assign threads to CPUs outside the CPU affinity set. Thanks to Ole Bjørn Hessen. [GL #2245]

  • When reconfiguring named, removing auto-dnssec did not turn off DNSSEC maintenance. This has been fixed. [GL #2341]

  • The report of intermittent BIND assertion failures triggered in lib/dns/resolver.c:dns_name_issubdomain() has now been closed without further action. Our initial response to this was to add diagnostic logging instead of terminating named, anticipating that we would receive further useful troubleshooting input. This workaround first appeared in BIND releases 9.17.5 and 9.16.7. However, since those releases were published, there have been no new reports of assertion failures matching this issue, but also no further diagnostic input, so we have closed the issue. [GL #2091]

Notes for BIND 9.16.10

New Features

  • NSEC3 support was added to KASP. A new option for dnssec-policy, nsec3param, can be used to set the desired NSEC3 parameters. NSEC3 salt collisions are automatically prevented during resalting. [GL #1620]

Feature Changes

  • The default value of max-recursion-queries was increased from 75 to 100. Since the queries sent towards root and TLD servers are now included in the count (as a result of the fix for CVE-2020-8616), max-recursion-queries has a higher chance of being exceeded by non-attack queries, which is the main reason for increasing its default value. [GL #2305]

  • The default value of nocookie-udp-size was restored back to 4096 bytes. Since max-udp-size is the upper bound for nocookie-udp-size, this change relieves the operator from having to change nocookie-udp-size together with max-udp-size in order to increase the default EDNS buffer size limit. nocookie-udp-size can still be set to a value lower than max-udp-size, if desired. [GL #2250]

Bug Fixes

  • Handling of missing DNS COOKIE responses over UDP was tightened by falling back to TCP. [GL #2275]

  • The CNAME synthesized from a DNAME was incorrectly followed when the QTYPE was CNAME or ANY. [GL #2280]

  • Building with native PKCS#11 support for AEP Keyper has been broken since BIND 9.16.6. This has been fixed. [GL #2315]

Notes for BIND 9.16.9

New Features

  • A new configuration option, stale-refresh-time, has been introduced. It allows a stale RRset to be served directly from cache for a period of time after a failed lookup, before a new attempt to refresh it is made. [GL #2066]

Bug Fixes

  • named could crash with an assertion failure if a TCP connection were closed while a request was still being processed. [GL #2227]

  • named acting as a resolver could incorrectly treat signed zones with no DS record at the parent as bogus. Such zones should be treated as insecure. This has been fixed. [GL #2236]

  • After a Negative Trust Anchor (NTA) is added, BIND performs periodic checks to see if it is still necessary. If BIND encountered a failure while creating a query to perform such a check, it attempted to dereference a NULL pointer, resulting in a crash. [GL #2244]

  • A problem obtaining glue records could prevent a stub zone from functioning properly, if the authoritative server for the zone were configured for minimal responses. [GL #1736]

  • UV_EOF is no longer treated as a TCP4RecvErr or a TCP6RecvErr. [GL #2208]

Notes for BIND 9.16.8

New Features

  • Add a new rndc command, rndc dnssec -rollover, which triggers a manual rollover for a specific key. [GL #1749]

  • Add a new rndc command, rndc dumpdb -expired, which dumps the cache database, including expired RRsets that are awaiting cleanup, to the dump-file for diagnostic purposes. [GL #1870]

Feature Changes

  • DNS Flag Day 2020: The default EDNS buffer size has been changed from 4096 to 1232 bytes. According to measurements done by multiple parties, this should not cause any operational problems as most of the Internet “core” is able to cope with IP message sizes between 1400-1500 bytes; the 1232 size was picked as a conservative minimal number that could be changed by the DNS operator to an estimated path MTU minus the estimated header space. In practice, the smallest MTU witnessed in the operational DNS community is 1500 octets, the maximum Ethernet payload size, so a useful default for maximum DNS/UDP payload size on reliable networks would be 1432 bytes. [GL #2183]

Bug Fixes

  • named reported an invalid memory size when running in an environment that did not properly report the number of available memory pages and/or the size of each memory page. [GL #2166]

  • With multiple forwarders configured, named could fail the REQUIRE(msg->state == (-1)) assertion in lib/dns/message.c, causing it to crash. This has been fixed. [GL #2124]

  • named erroneously performed continuous key rollovers for KASP policies that used algorithm Ed25519 or Ed448 due to a mismatch between created key size and expected key size. [GL #2171]

  • Updating contents of an RPZ zone which contained names spelled using varying letter case could cause some processing rules in that RPZ zone to be erroneously ignored. [GL #2169]

Notes for BIND 9.16.7

New Features

  • Add a new rndc command, rndc dnssec -checkds, which signals to named that a DS record for a given zone or key has been published or withdrawn from the parent. This command replaces the time-based parent-registration-delay configuration option. [GL #1613]

  • Log when named adds a CDS/CDNSKEY to the zone. [GL #1748]

Bug Fixes

  • In rare circumstances, named would exit with an assertion failure when the number of nodes stored in the red-black tree exceeded the maximum allowed size of the internal hash table. [GL #2104]

  • Silence spurious system log messages for an EPROTO(71) error code that was seen on older operating systems, where unhandled ICMPv6 errors resulted in a generic protocol error being returned instead of a more specific error code. [GL #1928]

  • With query name minimization enabled, named failed to resolve names that had extra labels to the left of the IPv6 part. For example, when named attempted query name minimization on a name like A.B., it stopped at the leftmost IPv6 label, i.e., without considering the extra labels (A.B). That caused a query loop when resolving the name: if named received NXDOMAIN answers, then the same query was repeatedly sent until the number of queries sent reached the value of the max-recursion-queries configuration option. [GL #1847]

  • Parsing of LOC records was made more strict by rejecting a sole period (.) and/or m as a value. These changes prevent zone files using such values from being loaded. Handling of negative altitudes which are not integers was also corrected. [GL #2074]

  • Several problems found by OSS-Fuzz were fixed. (None of these are security issues.) [GL !3953] [GL !3975]

Notes for BIND 9.16.6

Security Fixes

  • It was possible to trigger an assertion failure by sending a specially crafted large TCP DNS message. This was disclosed in CVE-2020-8620.

    ISC would like to thank Emanuel Almeida of Cisco Systems, Inc. for bringing this vulnerability to our attention. [GL #1996]

  • named could crash after failing an assertion check in certain query resolution scenarios where QNAME minimization and forwarding were both enabled. To prevent such crashes, QNAME minimization is now always disabled for a given query resolution process, if forwarders are used at any point. This was disclosed in CVE-2020-8621.

    ISC would like to thank Joseph Gullo for bringing this vulnerability to our attention. [GL #1997]

  • It was possible to trigger an assertion failure when verifying the response to a TSIG-signed request. This was disclosed in CVE-2020-8622.

    ISC would like to thank Dave Feldman, Jeff Warren, and Joel Cunningham of Oracle for bringing this vulnerability to our attention. [GL #2028]

  • When BIND 9 was compiled with native PKCS#11 support, it was possible to trigger an assertion failure in code determining the number of bits in the PKCS#11 RSA public key with a specially crafted packet. This was disclosed in CVE-2020-8623.

    ISC would like to thank Lyu Chiy for bringing this vulnerability to our attention. [GL #2037]

  • update-policy rules of type subdomain were incorrectly treated as zonesub rules, which allowed keys used in subdomain rules to update names outside of the specified subdomains. The problem was fixed by making sure subdomain rules are again processed as described in the ARM. This was disclosed in CVE-2020-8624.

    ISC would like to thank Joop Boonen of credativ GmbH for bringing this vulnerability to our attention. [GL #2055]

New Features

  • A new configuration option stale-cache-enable has been introduced to enable or disable keeping stale answers in cache. [GL #1712]

Feature Changes

  • BIND’s cache database implementation has been updated to use a faster hash function with better distribution. In addition, the effective max-cache-size (configured explicitly, defaulting to a value based on system memory or set to unlimited) now pre-allocates fixed-size hash tables. This prevents interruption to query resolution when the hash table sizes need to be increased. [GL #1775]

  • Resource records received with 0 TTL are no longer kept in the cache to be used for stale answers. [GL #1829]

Bug Fixes

  • Wildcard RPZ passthru rules could incorrectly be overridden by other rules that were loaded from RPZ zones which appeared later in the response-policy statement. This has been fixed. [GL #1619]

  • The IPv6 Duplicate Address Detection (DAD) mechanism could inadvertently prevent named from binding to new IPv6 interfaces, by causing multiple route socket messages to be sent for each IPv6 address. named monitors for new interfaces to bind() to when it is configured to listen on any or on a specific range of addresses. New IPv6 interfaces can be in a “tentative” state before they are fully available for use. When DAD is in use, two messages are emitted by the route socket: one when the interface first appears and then a second one when it is fully “up.” An attempt by named to bind() to the new interface prematurely would fail, causing it thereafter to ignore that address/interface. The problem was worked around by setting the IP_FREEBIND option on the socket and trying to bind() to each IPv6 address again if the first bind() call for that address failed with EADDRNOTAVAIL. [GL #2038]

  • Addressed an error in recursive clients stats reporting which could cause underflow, and even negative statistics. There were occasions when an incoming query could trigger a prefetch for some eligible RRset, and if the prefetch code were executed before recursion, no increment in recursive clients stats would take place. Conversely, when processing the answers, if the recursion code were executed before the prefetch, the same counter would be decremented without a matching increment. [GL #1719]

  • The introduction of KASP support inadvertently caused the second field of sig-validity-interval to always be calculated in hours, even in cases when it should have been calculated in days. This has been fixed. (Thanks to Tony Finch.) [GL !3735]

  • LMDB locking code was revised to make rndc reconfig work properly on FreeBSD and with LMDB >= 0.9.26. [GL #1976]

Notes for BIND 9.16.5

New Features

  • New rndc command rndc dnssec -status shows the current DNSSEC policy and keys in use, the key states, and rollover status. [GL #1612]

Bug Fixes

  • A race condition could occur if a TCP socket connection was closed while named was waiting for a recursive response. The attempt to send a response over the closing connection triggered an assertion failure in the function isc__nm_tcpdns_send(). [GL #1937]

  • A race condition could occur when named attempted to use a UDP interface that was shutting down. This triggered an assertion failure in uv__udp_finish_close(). [GL #1938]

  • Fix assertion failure when server was under load and root zone had not yet been loaded. [GL #1862]

  • named could crash when cleaning dead nodes in lib/dns/rbtdb.c that were being reused. [GL #1968]

  • named crashed on shutdown when a new rndc connection was received during shutdown. This has been fixed. [GL #1747]

  • The DS RRset returned by dns_keynode_dsset() was used in a non-thread-safe manner. This could result in an INSIST being triggered. [GL #1926]

  • Properly handle missing kyua command so that make check does not fail unexpectedly when CMocka is installed, but Kyua is not. [GL #1950]

  • The primary and secondary keywords, when used as parameters for check-names, were not processed correctly and were being ignored. [GL #1949]

  • rndc dnstap -roll <value> did not limit the number of saved files to <value>. [GL !3728]

  • The validator could fail to accept a properly signed RRset if an unsupported algorithm appeared earlier in the DNSKEY RRset than a supported algorithm. It could also stop if it detected a malformed public key. [GL #1689]

  • The blackhole ACL was inadvertently disabled for client queries. Blocked IP addresses were not used for upstream queries but queries from those addresses could still be answered. [GL #1936]

Notes for BIND 9.16.4

Security Fixes

  • It was possible to trigger an assertion when attempting to fill an oversized TCP buffer. This was disclosed in CVE-2020-8618. [GL #1850]

  • It was possible to trigger an INSIST failure when a zone with an interior wildcard label was queried in a certain pattern. This was disclosed in CVE-2020-8619. [GL #1111] [GL #1718]

New Features

  • Documentation was converted from DocBook to reStructuredText. The BIND 9 ARM is now generated using Sphinx and published on Read the Docs. Release notes are no longer available as a separate document accompanying a release. [GL #83]

  • named and named-checkzone now reject master zones that have a DS RRset at the zone apex. Attempts to add DS records at the zone apex via UPDATE will be logged but otherwise ignored. DS records belong in the parent zone, not at the zone apex. [GL #1798]

  • dig and other tools can now print the Extended DNS Error (EDE) option when it appears in a request or a response. [GL #1835]

Feature Changes

  • The default value of max-stale-ttl has changed from 1 week to 12 hours. This option controls how long named retains expired RRsets in cache as a potential mitigation mechanism, should there be a problem with one or more domains. Note that cache content retention is independent of whether stale answers are used in response to client queries (stale-answer-enable yes|no and rndc serve-stale on|off). Serving of stale answers when the authoritative servers are not responding must be explicitly enabled, whereas the retention of expired cache content takes place automatically on all versions of BIND 9 that have this feature available. [GL #1877]


    This change may be significant for administrators who expect that stale cache content will be automatically retained for up to 1 week. Add option max-stale-ttl 1w; to named.conf to keep the previous behavior of named.

  • listen-on-v6 { any; } creates a separate socket for each interface. Previously, just one socket was created on systems conforming to RFC 3493 and RFC 3542. This change was introduced in BIND 9.16.0, but it was accidentally omitted from documentation. [GL #1782]

Bug Fixes

  • When fully updating the NSEC3 chain for a large zone via IXFR, a temporary loss of performance could be experienced on the secondary server when answering queries for nonexistent data that required DNSSEC proof of non-existence (in other words, queries that required the server to find and to return NSEC3 data). The unnecessary processing step that was causing this delay has now been removed. [GL #1834]

  • named could crash with an assertion failure if the name of a database node was looked up while the database was being modified. [GL #1857]

  • A possible deadlock in lib/isc/unix/socket.c was fixed. [GL #1859]

  • Previously, named did not destroy some mutexes and conditional variables in netmgr code, which caused a memory leak on FreeBSD. This has been fixed. [GL #1893]

  • A data race in lib/dns/resolver.c:log_formerr() that could lead to an assertion failure was fixed. [GL #1808]

  • Previously, provide-ixfr no; failed to return up-to-date responses when the serial number was greater than or equal to the current serial number. [GL #1714]

  • A bug in dnssec-policy keymgr was fixed, where the check for the existence of a given key’s successor would incorrectly return true if any other key in the keyring had a successor. [GL #1845]

  • With dnssec-policy, when creating a successor key, the “goal” state of the current active key (the predecessor) was not changed and thus never removed from the zone. [GL #1846]

  • named-checkconf -p could include spurious text in server-addresses statements due to an uninitialized DSCP value. This has been fixed. [GL #1812]

  • The ARM has been updated to indicate that the TSIG session key is generated when named starts, regardless of whether it is needed. [GL #1842]

Notes for BIND 9.16.3

Known Issues

  • BIND crashes on startup when linked against libuv 1.36. This issue is related to recvmmsg() support in libuv, which was first included in libuv 1.35. The problem was addressed in libuv 1.37, but the relevant libuv code change requires a special flag to be set during library initialization in order for recvmmsg() support to be enabled. This BIND release sets that special flag when required, so recvmmsg() support is now enabled when BIND is compiled against either libuv 1.35 or libuv 1.37+; libuv 1.36 is still not usable with BIND. [GL #1761] [GL #1797]

Feature Changes

  • BIND 9 no longer sets receive/send buffer sizes for UDP sockets, relying on system defaults instead. [GL #1713]

  • The default rwlock implementation has been changed back to the native BIND 9 rwlock implementation. [GL #1753]

  • The native PKCS#11 EdDSA implementation has been updated to PKCS#11 v3.0 and thus made operational again. Contributed by Aaron Thompson. [GL !3326]

  • The OpenSSL ECDSA implementation has been updated to support PKCS#11 via OpenSSL engine (see engine_pkcs11 from libp11 project). [GL #1534]

  • The OpenSSL EdDSA implementation has been updated to support PKCS#11 via OpenSSL engine. Please note that an EdDSA-capable OpenSSL engine is required and thus this code is only a proof-of-concept for the time being. Contributed by Aaron Thompson. [GL #1763]

  • Message IDs in inbound AXFR transfers are now checked for consistency. Log messages are emitted for streams with inconsistent message IDs. [GL #1674]

  • The zone timers are now exported to the statistics channel. For the primary zones, only the loaded time is exported. For the secondary zones, the exported timers also include expire and refresh times. Contributed by Paul Frieden, Verizon Media. [GL #1232]

Bug Fixes

  • A bug in dnstap initialization could prevent some dnstap data from being logged, especially on recursive resolvers. [GL #1795]

  • When running on a system with support for Linux capabilities, named drops root privileges very soon after system startup. This was causing a spurious log message, unable to set effective uid to 0: Operation not permitted, which has now been silenced. [GL #1042] [GL #1090]

  • When named-checkconf was run, it would sometimes incorrectly set its exit code. It reflected only the status of the last view found; any errors found for other configured views were not reported. Thanks to Graham Clinch. [GL #1807]

  • When built without LMDB support, named failed to restart after a zone with a double quote (“) in its name was added with rndc addzone. Thanks to Alberto Fernández. [GL #1695]

Notes for BIND 9.16.2

Security Fixes

  • DNS rebinding protection was ineffective when BIND 9 is configured as a forwarding DNS server. Found and responsibly reported by Tobias Klein.:gl:#1574

Known Issues

  • We have received reports that in some circumstances, receipt of an IXFR can cause the processing of queries to slow significantly. Some of these were related to RPZ processing, which has been fixed in this release (see below). Others appear to occur where there are NSEC3-related changes (such as an operator changing the NSEC3 salt used in the hash calculation). These are being investigated. [GL #1685]

Feature Changes

  • The previous DNSSEC sign statistics used lots of memory. The number of keys to track is reduced to four per zone, which should be enough for 99% of all signed zones. [GL #1179]

Bug Fixes

  • When an RPZ policy zone was updated via zone transfer and a large number of records was deleted, named could become nonresponsive for a short period while deleted names were removed from the RPZ summary database. This database cleanup is now done incrementally over a longer period of time, reducing such delays. [GL #1447]

  • When trying to migrate an already-signed zone from auto-dnssec maintain to one based on dnssec-policy, the existing keys were immediately deleted and replaced with new ones. As the key rollover timing constraints were not being followed, it was possible that some clients would not have been able to validate responses until all old DNSSEC information had timed out from caches. BIND now looks at the time metadata of the existing keys and incorporates it into its DNSSEC policy operation. [GL #1706]

Notes for BIND 9.16.1

Known Issues

  • UDP network ports used for listening can no longer simultaneously be used for sending traffic. An example configuration which triggers this issue would be one which uses the same address:port pair for listen-on(-v6) statements as for notify-source(-v6) or transfer-source(-v6). While this issue affects all operating systems, it only triggers log messages (e.g. “unable to create dispatch for reserved port”) on some of them. There are currently no plans to make such a combination of settings work again.

Feature Changes

  • The system-provided POSIX Threads read-write lock implementation is now used by default instead of the native BIND 9 implementation. Please be aware that glibc versions 2.26 through 2.29 had a bug that could cause BIND 9 to deadlock. A fix was released in glibc 2.30, and most current Linux distributions have patched or updated glibc, with the notable exception of Ubuntu 18.04 (Bionic) which is a work in progress. If you are running on an affected operating system, compile BIND 9 with --disable-pthread-rwlock until a fixed version of glibc is available. [GL !3125]

Bug Fixes

  • Fixed re-signing issues with inline zones which resulted in records being re-signed late or not at all.

Notes for BIND 9.16.0

Note: this section only lists changes from BIND 9.14 (the previous stable branch of BIND).

New Features

  • A new asynchronous network communications system based on libuv is now used by named for listening for incoming requests and responding to them. This change will make it easier to improve performance and implement new protocol layers (for example, DNS over TLS) in the future. [GL #29]

  • The new dnssec-policy option allows the configuration of a key and signing policy (KASP) for zones. This option enables named to generate new keys as needed and automatically roll both ZSK and KSK keys. (Note that the syntax for this statement differs from the DNSSEC policy used by dnssec-keymgr.) [GL #1134]

  • In order to clarify the configuration of DNSSEC keys, the trusted-keys and managed-keys statements have been deprecated, and the new trust-anchors statement should now be used for both types of key.

    When used with the keyword initial-key, trust-anchors has the same behavior as managed-keys, i.e., it configures a trust anchor that is to be maintained via RFC 5011.

    When used with the new keyword static-key, trust-anchors has the same behavior as trusted-keys, i.e., it configures a permanent trust anchor that will not automatically be updated. (This usage is not recommended for the root key.) [GL #6]

  • Two new keywords have been added to the trust-anchors statement: initial-ds and static-ds. These allow the use of trust anchors in DS format instead of DNSKEY format. DS format allows trust anchors to be configured for keys that have not yet been published; this is the format used by IANA when announcing future root keys.

    As with the initial-key and static-key keywords, initial-ds configures a dynamic trust anchor to be maintained via RFC 5011, and static-ds configures a permanent trust anchor. [GL #6] [GL #622]

  • dig, mdig and delv can all now take a +yaml option to print output in a detailed YAML format. [GL #1145]

  • dig now has a new command line option: +[no]unexpected. By default, dig won’t accept a reply from a source other than the one to which it sent the query. Add the +unexpected argument to enable it to process replies from unexpected sources. [RT #44978]

  • dig now accepts a new command line option, +[no]expandaaaa, which causes the IPv6 addresses in AAAA records to be printed in full 128-bit notation rather than the default RFC 5952 format. [GL #765]

  • Statistics channel groups can now be toggled. [GL #1030]

Feature Changes

  • When static and managed DNSSEC keys were both configured for the same name, or when a static key was used to configure a trust anchor for the root zone and dnssec-validation was set to the default value of auto, automatic RFC 5011 key rollovers would be disabled. This combination of settings was never intended to work, but there was no check for it in the parser. This has been corrected, and it is now a fatal configuration error. [GL #868]

  • DS and CDS records are now generated with SHA-256 digests only, instead of both SHA-1 and SHA-256. This affects the default output of dnssec-dsfromkey, the dsset files generated by dnssec-signzone, the DS records added to a zone by dnssec-signzone based on keyset files, the CDS records added to a zone by named and dnssec-signzone based on “sync” timing parameters in key files, and the checks performed by dnssec-checkds. [GL #1015]

  • named will now log a warning if a static key is configured for the root zone. [GL #6]

  • A SipHash 2-4 based DNS Cookie (RFC 7873) algorithm has been added and made default. Old non-default HMAC-SHA based DNS Cookie algorithms have been removed, and only the default AES algorithm is being kept for legacy reasons. This change has no operational impact in most common scenarios. [GL #605]

    If you are running multiple DNS servers (different versions of BIND 9 or DNS servers from multiple vendors) responding from the same IP address (anycast or load-balancing scenarios), make sure that all the servers are configured with the same DNS Cookie algorithm and same Server Secret for the best performance.

  • The information from the dnssec-signzone and dnssec-verify commands is now printed to standard output. The standard error output is only used to print warnings and errors, and in case the user requests the signed zone to be printed to standard output with the -f - option. A new configuration option -q has been added to silence all output on standard output except for the name of the signed zone. [GL #1151]

  • The DNSSEC validation code has been refactored for clarity and to reduce code duplication. [GL #622]

  • Compile-time settings enabled by the --with-tuning=large option for configure are now in effect by default. Previously used default compile-time settings can be enabled by passing --with-tuning=small to configure. [GL !2989]

  • JSON-C is now the only supported library for enabling JSON support for BIND statistics. The configure option has been renamed from --with-libjson to --with-json-c. Set the PKG_CONFIG_PATH environment variable accordingly to specify a custom path to the json-c library, as the new configure option does not take the library installation path as an optional argument. [GL #855]

  • ./configure no longer sets --sysconfdir to /etc or --localstatedir to /var when --prefix is not specified and the aforementioned options are not specified explicitly. Instead, Autoconf’s defaults of $prefix/etc and $prefix/var are respected. [GL #658]

Removed Features

  • The dnssec-enable option has been obsoleted and no longer has any effect. DNSSEC responses are always enabled if signatures and other DNSSEC data are present. [GL #866]

  • DNSSEC Lookaside Validation (DLV) is now obsolete. The dnssec-lookaside option has been marked as deprecated; when used in named.conf, it will generate a warning but will otherwise be ignored. All code enabling the use of lookaside validation has been removed from the validator, delv, and the DNSSEC tools. [GL #7]

  • The cleaning-interval option has been removed. [GL !1731]


BIND 9 is open source software licensed under the terms of the Mozilla Public License, version 2.0 (see the LICENSE file for the full text).

The license requires that if you make changes to BIND and distribute them outside your organization, those changes must be published under the same license. It does not require that you publish or disclose anything other than the changes you have made to our software. This requirement does not affect anyone who is using BIND, with or without modifications, without redistributing it, nor anyone redistributing BIND without changes.

Those wishing to discuss license compliance may contact ISC at

End of Life

BIND 9.16 (Extended Support Version) will be supported until at least December, 2023. See for details of ISC’s software support policy.

Thank You

Thank you to everyone who assisted us in making this release possible.