Four Steps to the Right IOS

BY JASON RIDDLE

RELATED TOOLS Software Advisor Tool (Login Required) Cisco.com Case Query Tool (Login Required) IOS Release Notes Bug Toolkit (Login Required)

Network changes are inevitable. New applications, a growing user base, and changing business and network requirements can put unforeseen new demands on your networking operating system from the moment it is first deployed. For this reason, Cisco IOS® deployments should be thought of in terms of lifecycles, not as one-time events.

You can think of an IOS upgrade or first-time deployment as having four stages: the preparation stage to gather your requirements, the selection stage to choose the appropriate IOS releases, a testing stage to perform acceptance and certification testing of the network environment, and finally, the implementation stage.

Step 1. Preparation

Preparation requires two fundamental activities. The first is an understanding of the status and makeup of your network, and the second is defining the business requirements your network will need to support now and in the future. You will need to collect extensive information on the individual products, configurations, and feature requirements of your network before you can select the proper Cisco IOS Software Release. Management software can assist in gathering the needed information such as inventory and configurations. Feature requirements should be discussed among all stakeholders -- both on the business and engineering sides -- to account for current and future projects or applications.

Features

The names of the current IOS features used in your network can be obtained by using commands seen in the device configuration. The Cisco IOS command syntax tries to closely match the feature name with the command. If you are unsure about the feature name associated with a command, place the command in the Cisco.com search engine to identify the feature associated with it.

Example: 
Config Command: channel-group 1 mode on
CCO Search Results: Sample 
Configuration: EtherChannel Between 
Catalyst Switches
Feature Name: EtherChannel

Your projected feature list should identify the software required during the lifecycle of your planned IOS deployment. Make sure to take into account any projects currently on the horizon that may require additional networking functionality.

Step 2. Choosing the Right IOS

Choosing the appropriate release for your network environment requires the gathered information from the preparation stage and an understanding of Cisco IOS Software Release trains.

Early Deployment Releases

Cisco IOS Early Deployment releases are designed to introduce the latest innovative features to the market. This software puts you at the forefront of networking technology and allows you to evaluate new features and technologies within a test lab environment. These releases help align application adjustments to network configuration definitions before a production release is implemented.

Specific Market releases in this category target the unique requirements of service provider and enterprise networks. This targeted software includes the "S" train (12.0S) for service providers and the "E" train (12.1E) for the enterprise environment.

Consolidated Technology releases bundle new technologies from different network environments into one release. An example of this is the "T" train.

At the end of the Early Deployment development cycle, new features and platforms introduced in these trains are synched to the next Major (or Mainline) release.

Major Releases

Major ("M" train) releases are the primary deployment vehicles for Cisco IOS Software products. They consolidate features and hardware support from previous Early Deployment software. Maintenance revisions of Major releases provide increased reliability and quality of the software enhancements. Examples of M train releases include 12.0, 12.1, and 12.2.

General Deployment Releases

General Deployment status is attained when a release has significant market exposure and has been analyzed and qualified using specific stability metrics. Only Major releases are candidates for General Deployment status. After a release is selected, it enters a restricted maintenance phase. This ensures that new modifications to the code do not adversely affect the release. Examples of General Deployment releases include 12.0(8), 12.1(13) and later versions.

Feature Sets

Feature set selection rules allow configuration engineers to select only that group of features necessary to meet the needs of their unique environment. There are various feature sets and combinations to choose from: IP, IP Plus, Enterprise, Telco, for example.

Feature set and feature combination comparisons can be performed with the Software Advisor tool. Choose the "Software Support for Features" section, and then use the "Compare Releases" tool.

Selection Strategies

In many cases, there will be several IOS trains that meet the hardware and software requirements of your network. In these cases, you will want to maximize functionality while choosing the most mature release.

For optimal networks, classify each area of your network into feature categories such as core, distribution, and access. Each of these areas has its own requirements, so it's possible that a separate IOS release could be needed for each.

Using Software Advisor

The Software Advisor is the main tool used to find a Cisco IOS Software Release. First, you will use the tool to determine which IOS releases support your network's specific hardware. Then, the tool helps you compile a list of those releases that also support your specific feature requirements.

From the Software Advisor homepage, select "products running IOS" under the Software Support for Hardware section. You can search for your specific products by product family or part number -- matching each FRU (Field Replaceable Unit) identifier will ensure the correct parts are chosen. Select all the products in your network then click "Display Intersection" to display the common IOS releases that will support your hardware. This list will contain minimum releases required. For example, if it displays 12.1(2)T, every maintenance release after 2 will support the hardware (12.1(3)T, 12.1(4)T, 12.1(8)T, etc.).

Now that you have a release list for your specific hardware, it's time to input your feature requirements. From the Software Advisor home, select "Choose Software by Feature." Choose your platform and select all the features you will require to find the IOS releases that support them.

Now you can compare your hardware and feature release lists to find intersections and identify preferred IOS trains for each segment of your network.

Bugs, Changes, and Other Caveats

After you target the right IOS train for the platforms in your network, you should review all Release Notes for memory requirements, caveats, and new feature documentation. These can be found on Cisco.com.

To avoid caveats from affecting your deployment, open bugs should be reviewed using the Bug Toolkit on Cisco.com. The tool shows all bugs related to a particular IOS release. While most bugs won't affect all environments, it's important to make sure nothing will adversely affect your selected features and components.

If any identified bugs could affect your specific network environment, move to the fixed release in the "Fixed-in Version" field of the tool. If no fixed release is published, consider moving to a prior version that doesn't have the problematic bug ("Found-in Version" field indicates when a bug was initially identified).

Step 3. Testing/Validation

After you choose the appropriate IOS release, it should be validated in your network environment before full deployment. Your test plan should include current and projected features, and all features and configurations should be verified as "working as expected" before rolling out to the network at large.

Step 4. Implementation

Rolling out an IOS release into the network -- or any new software for that matter -- should be handled in a controlled and phased approach. A slow start upgrade scheme should be used to put the IOS on a few select devices. These test devices should be monitored for any unexpected behavior. After the devices have passed a test period, a full upgrade of devices can proceed.

Jason Riddle is a networking consulting engineer at Cisco. He can be reached at jriddle@cisco.com.

Hardware Supported	Features Supported	Common Releases	Preferred?	Why?
12.2(3)T	12.2(2)T	12.2(2)T or newer	NO	T Train, Early Deployment Release
12.2(2)	12.2(4)	12.2(4) or newer	YES	Mainline, Major Release
*****	12.1(6)E	12.1(6)E or newer	NO	E Train, Early Deployment Release

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