This document provides an overview of the Cisco 12000 Series Internet
Router software architecture.
Readers of this document should be knowledgeable of the
The information in this document is based on the following hardware:
The information in this document was created from the devices in a
specific lab environment. All of the devices used in this document started with
a cleared (default) configuration. If your network is live, make sure that you
understand the potential impact of any command.
For more information on document conventions, see the
Technical Tips Conventions.
Depending on the features you need, Cisco IOS®
software releases 11.2GS, 12.0S, or 12.0ST can be installed on a Cisco 12000
Series Internet Router. The choice should be made based on the features that
are required, the hardware parts that are installed, and the available memory.
Cisco IOS Software Release 12.0S is directly pulled from the Cisco IOS
Software 12.0 main line. It provides the combination of features, performance,
and platform support required by the Internet Service Provider (ISP) community.
Cisco IOS Software Release 12.0 S is the follow-up release to Cisco IOS
Software Release 11.1 CC. See
IOS Software Release 12.0S Early Deployment (ED) Release Summary.
Cisco IOS Software Release 12.0 ST is pulled from 12.0S and provides
new technology support. The driving factors in 12.0ST are Multi-Protocol Label
Switching (MPLS)/Virtual Private Network (VPN), Label Distribution Protocol
(LDP), Fast Re-Route, and high availability. For example, 12.0(16)ST introduced
MPLS-VPN support for the 12000 router 6xCT3 line card, as well as MPLS-VPN
support, VLAN to MPLS VPN mapping, and VLAN "P" bits mapping to IP Type of
Service (ToS)/MPLS Class of Service (CoS) bits on the 3xGE line card (LC).
A release such as Cisco IOS Software Release 12.0(16)S1 or 12.0(16)S2
includes bug fixes to the feature set in the maintenance image. For example,
Cisco IOS Software Release 12.0(19)S2 is a superset of 19S1, and 19S3 is a
super set of 19S2, and so on. Thus, a bug integrated in Cisco IOS Software
Release 12.0(16)S4 is not integrated in Cisco IOS Software Release 12.0(17)S or
12.0(18)S since these images were released before Cisco IOS Software Release
12.0(16)S4. However, fixes in Cisco IOS Software Release 12.0(16)S4 are
eventually integrated back into the 12.0S main release.
As from 12.0(22)S/ST, the ST train will merge to the S train and all
the features supported in the ST train will be supported in the S train. There
will be only one train for the Cisco 12000 Series Internet Router, the 12.0S
As a reference guide to decide which Cisco IOS software to install,
consult the Release Notes below. They give a detailed overview of the features
and hardware components that are supported for each Cisco IOS software release.
Software Advisor tool
(registered customers only)
is available to help you
choose the right Cisco IOS software release. Should you encounter any
conflicting information when using the Software Advisor, we recommend that you
rely on the Release Notes.
Once you have decided on a software release, you can download the image
from the Cisco web site. All the images are available to registered customers
Download Software Area
(registered customers only)
Installation and Upgrade Procedure for the Cisco 12000 Series for
If you experience problems during the Cisco IOS software installation
or upgrade, see
Recovery Procedure for the Cisco 12000 Series for troubleshooting steps
to help you recover.
After a Cisco IOS software upgrade, it might be necessary to upgrade
the microcode of some line cards to remove warning messages concerning line
card ROM Monitor or the fabric downloader warning messages. See
Line Card Firmware on a Cisco 12000 Series Internet Router for
instructions on how to do this.