ISC's Software Support Policy and Version Numbering
  • Updated on 11 Mar 2019
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ISC's Software Support Policy and Version Numbering

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The purpose of this statement is to help users determine how long a given ISC release is likely to be supported. This information is useful when deciding when to schedule a migration, or in some cases, to help determine which version to migrate to when updating.

For the most current information on the status of any particular software version, please refer to the software status listed on the downloads page.


Major versions

We have four types of major BIND 9 versions: Development, Stable, Extended Support version (ESV), and Supported Preview edition (also known as "Subscription").

Development versions

We release development versions off of the current working (master) branch. These will be the odd-numbered major versions, starting from BIND 9.13.

There is no fixed schedule to minor development releases; new minor versions will be made available as new features or changes become ready for field testing. Development version minor releases introduce new and updated features and may not be backward-compatible with their immediate predecessor. Development versions of BIND are suitable for those interested in experimenting with and providing feedback to ISC upon their features. There will be no alpha/beta/release candidate versions of development versions, and it may sometimes happen that a recently-released minor version is superseded very quickly in order to address a flaw. We may not issue -P releases for development versions with security bugs, at our discretion.

Development versions will be supported for 12 months. At the end of the 12-month period, the stabilized development version will be re-labeled and re-released as the next Stable version, and we will begin a new development branch.

Stable versions

Historically, we have recommended waiting until the third maintenance release of a new branch before deploying it in large-scale production. Beginning with BIND 9.14, we plan to publish a new Stable version annually. We will stabilize all the even-numbered major versions for production use – for example, BIND 9.14 and BIND 9.16. Each major branch will have a series of minor releases, such as BIND 9.14.0, 9.14.1, etc. Minor releases on a Stable version will include bug fixes only, to maximize stability.

Stable branches of BIND are fully supported for 12 months, but will be EOL (End of Life) as soon as the next Stable version is released, unless designated as an Extended Support Version.

Extended Support versions (ESV)

Every other Stable version will be designated for Extended Support, and will be supported for at least four years from initial release. Organizations with a long internal validation, integration, or deployment cycle should consider using these versions.

Here is our current ESV version:

  • BIND 9.11 is an Extended Support version, and will be supported until December, 2021.

BIND 9.16 will be our next ESV, followed by BIND 9.20; every second stable version after that will be ESV.

Supported Preview edition (also known as "Subscription," marked -S)

Releases marked with a -S are part of ISC’s Supported Preview edition. These releases provide a deployable, supported vehicle for our support customers to receive early access to new features in development. The -S edition is created for and available to support subscribers, and may also be offered to community developers for testing and feedback. The -S edition includes select unreleased software (new features and other changes) that ISC judges to be stable enough for production use. The software released in the -S versions will usually be available for experimental use via our public code repository and is intended for eventual general public release. Features in the -S version may still be in development and may be changed or even removed by the time of the public release.

The -S edition releases are actively maintained and patched in case of security vulnerabilities, just as our regular public releases are. The -S edition is offered under the same license terms as the open source BIND 9, but redistribution is constrained by the support agreement between ISC and the support subscriber.

The support plan is different from regular releases:

  1. When we put out a new maintenance release, we do a corresponding -S1 that will normally include all the bug fixes in the maintenance release, and will normally be a superset of the code in the corresponding maintenance version.
  2. If we have to do a security patch (-P), we do a corresponding -S for the -S edition. For example, if we were issuing a 9.9.8-P1, and the current release of the S edition was 9.9.8-S1, the corresponding security release for the -S edition would be numbered 9.9.8-S2.
  3. We will add changes (new features) to the -S edition between maintenance releases that we would not add to to a maintenance release of the public edition.
  4. We will not support more than one -S edition release on any given branch.
  5. When we start producing an -S edition on a new branch, we will continue to support the -S edition on the prior branch for another six months to support migration.

Minimal Security Updates

All supported versions of BIND 9 may occasionally receive unscheduled releases in response to a critical security bug; in that case, the changes introduced between that version and its predecessor will be minimal and necessary only.


Here are our current versions and their EOL dates:

  • DHCP 4.1-ESV was originally scheduled to go to EOL in December 2015, but we have extended this indefinitely to maintain a smaller-footprint edition.
  • DHCP 4.4 is the current ESV version. At this point, no EOL is established.

We are nearing the end of maintenance for ISC DHCP (relative to its 20-year lifespan). The exact timeframe for EOL will depend on the maturity of Kea and other available alternatives. As we approach EOL for ISC DHCP, we may begin adding minor new features in point releases and make other exceptions to our customary support policies.

Extended Support Versions (ESV)

Releases designated as ESV are ISC’s Extended Support versions. We used to incorporate the letters ESV into the version name, but we discontinued this practice after DHCP 4.1ESV.

Once the ESV designation has been assigned to a given major release we will avoid introducing any new features or functionality changes. (Exceptions may be made where the feature is of significant benefit to the user community, but in those cases, the new functionality will be enabled via a compile-time option.) However, we will install all significant and applicable bug fixes into ESVs. Each ESV will be supported for at least four years from the initial release of that major version.


All Kea releases to date include new features and are considered development releases. We will continue doing this to keep up with the pace of new development until further notice. Currently, we are issuing updates every 4-6 months, and there is no such thing as a maintenance-only release. ISC offers support for the current, and immediate prior, regularly-released versions of Kea. As the product matures, we plan on supporting both maintenance and development branches.

  • Kea 1.3 went to EOL in December 2018
  • Kea 1.4 will be supported until July 2019 (or until we release Kea 1.6)
  • Kea 1.5 will be supported until December 2019 (or until we release Kea 1.7)

Other General Policy Guidelines

  • Standard support terms do not apply to developmental releases, the Supported Preview edition, or alpha, beta, and Release Candidates (RCs). These are typically shorter-lived releases.
  • We reserve the right to change our version numbering for Kea.
  • We also reserve the right, based on these changes, to include some minor features in point releases (e.g. 9.8.1) for BIND 9 and ISC DHCP.
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