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Understanding Junos release numbering for SRX platforms



Article ID: KB30092 KB Last Updated: 09 May 2019Version: 6.0
The Junos versions for SRX that were released between 2013 and 2017, have a release name with the letter 'X' in it. For example "15.1X49-D170". Those releases are commonly referred to as SRX X-releases.

This article explains what naming convention and logic the SRX X-releases adhere to. It also lists the major releases which have been released for SRX platforms over the last several years.


Like other Juniper Networks platforms, SRX security gateways are running Junos software. Since the beginning of 2013 new Junos releases for SRX have adopted a naming convention using the letter 'X'. Note that from Junos version 17.3 onwards, SRX platforms returned to using the regular Junos releases again, which are also used by other Juniper Networks platforms.

X-release naming convention

Let's take release 12.1X44-D10 as an example. This release name consists of the following components.

  ^     ^     ^
  |     |     |
  |     |     | D10 - the maintenance release number
  |     |
  |     | X44 - the X-release number
  12.1 - the Junos version that this X-release is based upon

12.1X44 - the base Junos version and X-release number together designates the major release (version) number. This is comparable with for example 11.4 in common Junos.

D10 - this suffix designates the specific release number. This is comparable with R1 in common Junos.

Using "D" in release numbering

As mentioned above, the X-releases use the "Dxx" suffix instead of "Rxx" to indicate the maintenance release(*) number.

Unlike with "R" numbers in common Junos, the "D" numbers do not start at 1 and count up from there. Instead, it works as follows.

The first release shipping (FRS) in X-releases is the D10 release.  From 12.1X44 release till the 12.3X48 release, the second maintenance release will be D15. The third maintenance release is D20 and so on. So the maintenance release number counts up with steps of 5 at a time. From 15.1X49 release onward, the second maintenance release will be D20. The third maintenance release is D30 and so on. So the maintenance release number counts up with steps of 10 at a time.

Generally, service releases(*) are planned in between the maintenance releases. Service releases get the numbers allocated between the maintenance release numbers. For example: D11, D12, D13, D14. If needed, some of these in-between numbers can also be allocated to customer special releases.

Respin number

All Junos releases have a respin number at the end of the image name. For example Junos release 12.1X44-D10 can also be written as 12.1X44-D10.4, where the .4 is the respin number. You will see this number in the Junos image file name and in the CLI command output for 'show version'. However, for official releases the respin number can be disregarded.

The reason why the respin number is there is that during quality assurance testing before releasing the image, some issues may be found and addressed before release. Every time when a new build of the same release is compiled, the new build will get its respin number increased by one.

In the end, only the final respin will be officially released. For this reason, the specific respin number can be considered irrelevant and disregarded for official public Junos releases (i.e. FRS/maintenance releases and service releases).

X-release life span

As with common Junos releases, also the SRX X-release trains can have different supported lifetimes. A major release can be either an EEOL (extended end-of-life) release or a regular EOL release. This determines for how much time they will be supported. The exact milestone dates for each Junos release can be found at the Junos Dates and Milestones page.

Generally, EEOL releases will receive 36 months of Juniper Networks engineering support after FRS. In addition, another 6 months of JTAC support will be provided. Regular EOL releases will receive 24 months of Juniper Networks engineering support after FRS. In addition, another 6 months of JTAC support will be provided. However there can be exceptions to this rule for some releases, so always check the official Junos Dates and Milestones page for the applicable dates.

After engineering support has ended, no further release will be planned for that release train and hence no additional bug fixes for that major release will be available. Any potential software issues will then be addressed in a higher, supported major release.

SRX releases overview

For SRX platforms, the following major releases have been released since Junos 11.4.

11.4 - E-EOL
12.1X44 - E-EOL
12.1X46 - E-EOL
12.3X48 - E-EOL
15.1X49 - E-EOL

For the applicable FRS and EOS/EOL dates please refer to the Junos Dates and Milestones page.

For the most updated list of Junos releases available for SRX platforms, please see the Software Downloads.


(*) Definition of Maintenance Releases and Service Releases:

  • Maintenance Releases - Standard releases provided to support customers running the Junos OS to provide fixes in shipped version releases. The software download page links to whatever is the latest revision available.
  • Service Releases - Targeted releases to provide more timely delivery of critical fixes to meet customer needs. Service releases may be limited to specific platforms or use cases. The service releases are available through JTAC.

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