Updating cisco ios 2600
Starting with Cisco IOS release 15, there is just a single train, the M/T train.
This train includes both extended maintenance releases and standard maintenance releases.
Rebuilds are produced to either quickly repair a defect, or to satisfy customers who do not want to upgrade to a later major revision because they may be running critical infrastructure on their devices, and hence prefer to minimise change and risk.
Interim releases – Are usually produced on a weekly basis, and form a roll-up of current development effort.
Most Cisco products that run IOS also have one or more "feature sets" or "packages", typically eight packages for Cisco routers and five packages for Cisco network switches.
For example, Cisco IOS releases meant for use on Catalyst switches are available as "standard" versions (providing only basic IP routing), "enhanced" versions, which provide full IPv4 routing support, and "advanced IP services" versions, which provide the enhanced features as well as IPv6 support.
In all versions of Cisco IOS, packet routing and forwarding (switching) are distinct functions.
Routing and other protocols run as Cisco IOS processes and contribute to the Routing Information Base (RIB).
For example, 12.1(8)E14 is a Rebuild, the 14 denoting the 14th rebuild of 12.1(8)E.
This is processed to generate the final IP forwarding table (FIB, Forwarding Information Base), which is used by the forwarding function of the router.
On router platforms with software-only forwarding (e.g., Cisco 7200) most traffic handling, including access control list filtering and forwarding, is done at interrupt level using Cisco Express Forwarding (CEF) or d CEF (Distributed CEF).
Cisco recommend upgrading to Maintenance releases where possible, over Interim and Rebuild releases.
Cisco says, "A train is a vehicle for delivering Cisco software to a specific set of platforms and features." Before Cisco IOS release 15, releases are split into several trains, each containing a different set of features.