Junos Service Release software - "Junos SR" or SR, is a type of maintenance release issues between Software Maintenance releases - eg: 21.2R3 , 21.2R4 etc. SR provides critical fixes for bugs etc. These release are available in the Juniper downloads page. Here are the steps on how to download the Junos SR releases. 


> Open the Downloads page using the link: 
https://support.juniper.net/support/downloads/

> Under 'Find a Product' search for 'SRX320'

> Under 'Download Results for:  SRX3400' you will see Select OS and a dropdown.

> Click on the dropdown and select 'Junos SR'

> Click on the dropdown near Version and select 21.4.

> Scroll down a bit and you can see the version 21.4R3-S5 listed on top.

> Click on the tgz link near the version.

> It will prompt for login. Please login using your registered email id and click on I Agree

> In the next page you will see 'To download the image on your localhost,

> Click there and download the software to your computer.