Whenever we plan to upgrade Cisco devices or if we need to upgrade or downgrade the firmware due to any vulnerability we get too many available firmware which is generally tagged with few abbreviations like ED, LD, DG, DF, etc. Sometimes it really becomes difficult to select the most reliable and best firmware or software of our devices that are already in production. Below is the brief details of the different type of Cisco firmware or software releases.
The Cisco IOS Software image is either ED, LD, GD, or DF:
Early Deployment releases offer new features, platforms, or interface support. Most non-major releases contain Early Deployment releases. These releases are marked as “ED” on the Cisco Software Download portal.
A General Deployment Cisco IOS software is considered as the most reliable and trusted IOS which is suitable for deployment anywhere in-network as per requirement. General Deployment Cisco IOS goes through testing and bug fixes and also Customer feedback surveys from production and test networks using the releases. Only major releases are going for the General Deployment milestone. One could see “GD” mentioned on the release if it is General Deployment released IOS.
A major release of Cisco IOS Software is said to be in the “Limited Deployment” phase of its life cycle during the period between its first shipment and the GD milestone. Limited Deployment marked as “LD” in Cisco IOS.
As its name suggests, Deferred releases are discontinued images which are not available for download, and also these releases should not be used in production. Releases are called Deferred due to known defects. They are termed as “DF” for Cisco IOS.
Interim releases contain bug fixed which addresses specific issues found since the last feature or maintenance release. These are fully supported by Cisco TAC. “Interim” releases generally do not go through a full regression test. These releases get tested for an individual bug fix.
As per Cisco, it is recommended to use General Deployment Cisco IOS or firmware in production because they are widely used, fully tested, and reliable.
Sometimes some IOS also has bugs which cause issues after the upgrade. Please, refer Planning Upgrade Cisco ASA To 9.14.1? to know the bugs.
Source: Cisco, Internet, Knowledge Base