Cisco IOS Trains
A Cisco IOS Train is used to deliver Cisco IOS releases that evolve from a common code base.
In recent years, with the addition of thousands of new features, hundreds of new applications, and a wide array of platforms, Cisco IOS software has diversified from one train to multiple trains of releases in order to support different feature sets for different customer needs.
Below lists the types of Cisco IOS release trains:
Train / Release | Description | Examples |
| Mainline | Consolidates releases and fixes defects. Inherits features from previous generation T train, and does not add additional features. | 12.2, 12.3, 12.4. |
| T (Technology) | Introduces new features and fixes defects. Provides support for new hardware. | 12.2T, 12.3T. |
| S | Supports high-end backbone routing, and fixes defects. | 12.0S, 12.2S. |
| SB | Targets at SP edge networks. Supports broadband and leased-line aggregation, and MPLS Provider Edge (PE). | 12.2SB. |
| SE, SG. | Supports mid-range and low-end Ethernet LAN switching for Enterprise access and distribution networks, as well as mid-range and low-end SP Metro Ethernet networks. | 12.2SE, 12.2SG. |
| SR | Targets at high-end SP Carrier Ethernet, Broadband Aggregation and Subscriber Services, Metro Ethernet, and MPLS Provider Edge (PE) networks. | 12.2SR. |
| SX | Designed for at core and data center networks, enterprise campus, and service provider edge networks that require world-class IP and MPLS services. Supports high-end Ethernet LAN switching for access, distribution, core, and data center networks. | 12.2SX. |
| E | Targets at enterprise core and SP edge networks. Supports advanced QoS, voice, security, and fixes defects. | 12.1E. |
| B | Supports broadband features and fixes defects. | 12.2B, 12.3B. |
Mainline and T Train Relationship
Cisco uses at least the following 2 trains for releasing Cisco IOS software. With 2 trains, new features can be introduced in a release without affecting the code base of the mainline train.
i) Mainline train – A train for mainline bug fixes. Does not incorporate new features.
ii) T train – A train for synchronized mainline bug fixes and new features.
Note: Bug fixes to maintenance releases on a mainline train are synchronized with subsequent maintenance releases on the child T train.
Mainline trains (eg: 12.2) are built from previous generation T trains (eg: 12.1T). Mainline trains (eg: 12.2) are parents of other T trains (eg: 12.2T). Ex: 12.1T > 12.2 > 12.2T > 12.3 > 12.3T.
Cisco IOS Image Naming Convention
Cisco IOS Naming Convention
Below lists the Memory Location codes:
| Code | Description |
| f | The image runs from Flash memory. |
| m | The image runs from RAM. |
| r | The image runs from ROM. |
| l | The image is relocatable. |
Below lists the Compression Format codes:
| Code | Description |
| z | The image is compressed in zip format. |
| x | The image is compressed in mzip format. |
Interim Builds are software from the Cisco IOS engineering build processes that the Cisco TAC released to customers to address a specific issue on temporary basis. Customers who have an interim build running on their network devices should contact Cisco TAC for assistance for replacing the interim build.
An interim build name has a train number plus a maintenance release number and decimal number in parentheses, eg: 12.2(3.1).
Unlike conventional computer software versioning rules, a 12.3 IOS release is not necessary newer than a 12.2 IOS release, eg: a maintenance release of 12.2T can be released few months later than a maintenance release of 12.3.
Cisco IOS binary image name examples:
| Image Name | Description |
| c3725-entbase-mz-123-2.T.bin | 12.3(2)T release with the Enterprise Base Feature set for the Cisco 3725 platform. |
Cisco IOS Packaging
Cisco IOS Packaging
Cisco IOS consists of 8 packages for Cisco routers and 5 packages for Catalyst switches.
4 packages are designed to satisfy the requirements of the following 4 service categories:
- IP data
- Converged voice and data
- Security and VPN
- Enterprise protocols
3 additional premium packages offer new IOS features that address more complex network requirements. All features merge in the Advanced Enterprise Services that integrates support for all routing protocols with voice, security, and VPN capabilities.
Feature Inheritance > After a feature is introduced, it will be included in the more comprehensive packages. This clarifies the feature contents of different packages and the relationship between them, which facilitates IOS image and feature selection during migration.
New Cisco IOS packaging naming convention:
| Base | Entry-level image – IP Base, Enterprise Base. |
| Services | Addition of IP Telephony Service, MPLS, VoIP, VoFR, and ATM – SP Services, Enterprise Services. |
| Advanced | Addition of VPN, Cisco IOS Firewall, 3DES Encryption, SSH, IPSec and IDS – Advanced Security, Advanced IP Services. |
| Enterprise | Addition of multi-protocols, eg: IBM, IPX, AppleTalk – Enterprise Base, Enterprise Services. |
Cisco IOS Deployment
Early Deployment (ED) releases provide new features and new platform and interface support in addition to bug fixes. There are 4 variations of the ED releases:
- Consolidated Technology Early Deployment (CTED). These are also known as the T train and are easily identifiable by their name, which always ends with a T (Technology), eg: 12.2T and 12.3T. T trains are very rich in features, protocols, and platforms support.
- Specific Technology Early Deployment (STED). STEDs are usually platform-specific. Ex: 11.1CA, 11.1CC, 11.1CT, 11.3NA, 11.3MA, 11.3WA, and 12.0DA.
- Specific Market Early Deployment (SMED). SMEDs are similar to STEDs, but they target specific market segments, eg: ISPs. Ex: 12.0S, and 12.1E.
- Short-lived Early Deployment, also known as X Releases (XED). XEDs do not provide regular software maintenance revisions. If a bug is found in the XED before its convergence with the CTED, a software rebuild is initiated and a number is appended to the IOS name. Ex: 12.0(2)XB1 and 12.0(2)XB2 are the rebuilds of 12.0(2)XB.
A General Deployment (GD) release is major Cisco IOS software that reaches its GD milestone in its lifecycle and Cisco feels that it is suitable for deployment anywhere in customer networks where the features and functionalities of the release are required. Criteria for reaching the GD milestone are based on, but not limited to: customer feedback surveys from production and test networks using the release, customer engineer bug reports, and reported field experience. Only major releases are candidates to reach the GD milestone.
A Limited Deployment (LD) release is major Cisco IOS software that reaches the LD phase of its lifecycle during the period between its FCS (First Customer Shipment) and the GD milestone.
Note: GD and LD releases are not applicable to any future Cisco IOS maintenance releases or rebuilds starting from Cisco IOS Software Release 12.4
Deferred (DF) releases are not available for download due to known critical defects as announced by a Deferral Advisory. These releases should not be running on production routers and customers are strongly urged to migrate from the affected image to the replacement image as advised in the Deferral Advisory.
Maintenance Deployment (MD) releases provide bug fixes and ongoing software maintenance.
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