Differences
between IOS and IOS XE
Cisco IOS:
- IOS is monolithic, completely adherent to the hardware,
and does not provide any kind of isolation between “processes”, neither
from a CPU nor memory point of view.
- Virtual memory is shared by all IOS processes: nothing
prevents buffer overflows.
- Scheduler is non-preemptive: if SNMP decides it should
keep CPU busy, it can, and other processes (BGP…) will be prevented from
running.
- You cannot upgrade IOS (or parts of it) without
disruption unless you are running expensive dual-supervisor hardware.
Cisco IOS-XE:
IOS XE retains the exact same look
and feel of IOS, changing in some commands due to his ability to be used in
multi-core CPU providing enhanced features and improved functionality, high
availability, distributed software architecture and modularity.
Cisco
IOS XE Software is a modular operating system built on a Linux kernel. The Linux
kernel is designed to meet greater requirements for security and high
availability. IOS XE includes a software module derived from the Cisco IOS
Software. In IOS XE, IOS 15.0 runs as a single
daemon within a modern Linux operating system.
- Additional system functions now run as additional,
separate processes in the host OS environment.
- The actual IOS XE software comes in seven individual
sub-packages (files) which are combined into a complete consolidated
package (file). See below.
Allowing these routers to use
Cisco IOS software redundancy, Cisco high-availability features, Nonstop
Forwarding (NSF), and In Service Software Upgrades (ISSUs). This option
requires for example the Cisco ASR 1000 Series Route Processor to have 4 GB of
DRAM memory.
Cisco IOS XE Software and
introduce a distributed software architecture that moves many operating system
responsibilities out of the IOS process. In this architecture, Cisco IOS, which
previously was responsible for almost all of the internal software processes,
now runs as one of many Cisco IOS XE processes while allowing other Cisco IOS
XE processes to share responsibility for running the router.
Software Packaging
A Cisco IOS XE Software
image consists of seven individual modules (also referred to as subpackages).
Individual modules or subpackages of a Cisco IOS XE Software image cannot be
downloaded from Cisco.com individually. Example Individual subpackages can be
extracted from the consolidated package from the Cisco ASR 1000 Series router
command-line interface (CLI). Figure 1 illustrates how individual software
subpackages are bundled in Cisco IOS XE Software.
Cisco IOS-XE software use a new software
packaging model consisting of:
Consolidate
package
Individual
software sub=packages within a consolidated package
Optional
software sub=packages outside of consolidated packages
Each
Cisco IOS XE consolidated package contains a collection of individual software
sub-packages.
Each
individual software sub-package is an individual software file that controls a
different element or elements of the Cisco ASR 1000 Series Router. Some
individual sub-packages may be installed per element (for example, per SPA).
Note: the sub-package functionality is intended for both
upgrade and field support, and not all combinations of sub-packages are
supported.
Each
individual software sub-package can be upgraded individually, or all individual
software
Sub-packages
for a specific Cisco IOS XE consolidated package can be upgraded as part of a
complete
Cisco
IOS XE consolidated package upgrade.
Importantly,
IOS (the RPIOS individual software sub-package) is considered one of the
individual
software
sub-packages that makes up the complete Cisco IOS XE consolidated package.
The following are the individual
software sub-packages within a consolidated package:
• Route Processor
RPBase: Provides
the operating system software for the route processor
RPControl: Provides the control-plane processes that
interface between Cisco IOS Software and the rest of the platform.
RPIOS: Provides the Cisco IOS Software kernel, which
is where Cisco IOS Software features
are
stored and run; each consolidated image variant has a different RPIOS
sub-package:
RPIOS-ipbase, RPIOS-ipbasek9, RPIOS-advipservices,
RPIOS-advipservicesk9,
RPIOS-adventservices,
and RPIOS-adventservicesk9.
-==============================================================
Note:
The
RPIOS-advipservices and RPIOS-adventservices sub-packages are only available
beginning
with
Cisco IOS XE Release 2.2.1 and later releases. These two sub-packages are not
available
with
Cisco IOS XE Release 2.1.2 and earlier releases.
-============================///-==================================
RPAccess: Provides components to manage enhanced
router access functionality.(ssh)
ESPBase: Provides the ESP operating system and
control processes and the ESP software.
SIPBase: Share interface processor (SIP) carrier card operating system and control processes.
SIPSPA: Provides the shared port adaptor (SPA)
driver and associated field-programmable device (FPD) images
A Cisco IOS XE
consolidated package allows users to upgrade all individual software
sub-packages on
the router with
a single Cisco IOS XE image download. The Cisco IOS XE consolidated packages available
vary based on the Route Processor (RP1 or RP2) installed in the system and the
Cisco IOS XE Release.
Note
- Normally, the router boots from the single consolidated
package which automatically loads each of the seven sub-packages into
memory.
- However, you can extract individual sub-packages
yourself and specify which sub-packages you want loaded (maybe 5 instead
of all 7).
- When individual sub-packages are loaded “content from
the RP is copied into memory on an as-needed basis only” which conserves
memory.
- The router can run at highest peak traffic load when
configured to run using individual sub-packages.
- IOS XE Software architecture
Why IOS XE?
The IOS feature set for routing and
switching is unmatched in the industry, delivering functionality required for
business critical applications. Preserving these advantages of IOS to our
customers is critical for Cisco.
IOS XE retains the exact same look
and feel of IOS, while providing enhanced future-proofing and improved
functionality. In IOS XE, IOS 15.0 runs as a single daemon within a modern
Linux operating system. Additional system functions now run as additional,
separate processes in the host OS environment. The operation, support and
management of IOS XE does not require re-training from classic IOS.
Running IOS and other applications
as separate processes also enables load balancing the multi-core CPU, allowing
each process to use a different core. IOSd within the IOS XE environment
supports multiple threads and multi-core CPUs.
Control Plane and Data Plane Separation
IOS XE introduces an opportunity to
enable teams to now build drivers for new Data Plane ASICs outside the IOS instance
and have them program to a set of standard APIs which in turn enforces Control
Plane and Data Plane processing separation.
IOS XE accomplishes Control Plane /
Data Plane separation through the introduction of the Forwarding and Feature
Manager (FFM) and its standard interface to the Forwarding Engine Driver (FED).
FFM provides a set of APIs to Control Plane processes. In turn, the FFM
programs the Data Plane via the FED and maintains forwarding state for the
system. The FED is the instantiation of the hardware driver for the Data Plane
and is provided by the platform.
Since, historically, IOS has served
as an Operating System as well as providing the key Routing Infrastructure,
there has always been an aspect of Platform Dependent (PD) and Platform
Independent (PI) code within IOS. IOS XE allows the platform dependent code to
be abstracted from a single monolithic image. By moving drivers outside of IOS,
IOS XE enables a more purely PI-focused IOS process. This provides a more efficient
software delivery model for both the core IOS team, as well as platform
developers, since the software can be developed, packaged and released
independently.
Prior to IOS XE, the only way to
integrate functionality into an IOS product was to either port the
functionality into the IOS operating system or run the functionality on a
service blade outside of IOS. This model has fundamentally constrained how
quickly Cisco can integrate homegrown features, products through acquisition,
or third party applications.
IOS XE permits the integration of
non-IOS applications through the following mechanisms:
• Standard Linux-based environment
for hosting applications;
• Extending IOS functionality into
peripheral applications through well-defined APIs exported via Linux-shared
client libraries;
• Provide a robust management
infrastructure called Common Management Enabling Technology (COMET) that allows
for CLI, XML, SNMP, and HTTP-based management of integrated applications.
IOS XE Software Architecture
The IOS XE foundation is a POSIX
environment along with Free and Open Source Software (FOSS) for the common
drivers, tools and utilities needed to manage the system. In addition to the
standard set of off-the-shelf drivers, IOS XE is comprised of a set of Cisco
specific drivers and associated chassis/platform management modules.
On top of the base operating system
and drivers, IOS XE provides a set of infrastructure modules which define how
software is installed, how processes are started and sequenced, how
high-availability and software upgrades are performed and, lastly, how the
applications are managed from an operational perspective. The core
application that runs on top of this new infrastructure is the IOS feature set.
Cisco products immediately reap the benefits of an extensive feature set for
routing and switching platforms that has been built into IOS over the years.
Customers can expect the same features to be available and for them to perform
and be managed in the exact same way as previous products.
Finally, the evolved IOS
architecture is specifically designed to accommodate other applications outside
of IOS. These applications can either be tightly integrated with IOS or they
could run side-by-side with IOS with very little or no interactions. These
applications can be upgraded or restarted independently of IOS. If an
application does require services from IOS, it integrates with IOS through a
set of client libraries called "service points". These service points
generically extend IOS information and services to outside applications such
that these services are not replicated or managed separately.
IOS XE looks and feels the same as
the IOS that we all know. There is almost no change in the different feature
configurations, making the migration and user experience consistent with IOS.
If you know how to operate IOS today, you already know how to operate IOS XE.
The only minor difference in the CLI, and some outputs, is due to the
customization that reflects the process-oriented approach of IOS XE, and the
ability to use a multi-core CPU.
-================FAQ-==================
Is Cisco IOS. XE another operating system at Cisco?
A. Absolutely
not! Cisco IOS XE is a representation of the continuing evolution of Cisco IOS
Software to support our next-generation platforms. Cisco IOS XE itself has been
shipping on the ASR-1000 since 2008 and Cisco IOS XE 3 SG has been shipping on
the new Catalyst. 4500-E Series since October 2010. It provides an improved
software architectural strategy, while maintaining all the benefits and
familiar manageability interface of the long IOS legacy.
Q. What are
the benefits of IOS XE over IOS?
A. There are
multiple benefits of the transition from IOS to IOS XE that the end-users will
enjoy. IOS XE will help lower the Total Cost of Ownership of many Cisco
solutions by offering enhanced services integration for enhanced functionality
within the network. In addition, it supports multiple CPU cores, control plane
and data plane separation, and platform abstraction.
Q. Do I need
to train my staff or change anything in my management platform?
A. No, Cisco
IOS XE looks like and is managed the same way as traditional Cisco IOS
Software. Only a handful of commands have changed, such as "show
processor" and "show memory," which had to be extended to
account for the multicore CPUs that Cisco IOS XE now supports. Otherwise, if
you know how to manage Cisco IOS Software, you know how to manage Cisco IOS XE
Q. What, if
anything, does Cisco IOS XE share with Cisco IOS Software Release 15?
A. Cisco IOS
XE contains Cisco IOS Release 15 within itself. Cisco IOS Software runs as a
process within Cisco IOS XE in what is called the IOS daemon, or IOSd. While many
of the infrastructure components have migrated from Cisco IOS itself to Cisco
IOS XE-such as High Availability- the features of Cisco IOS Software are
exactly the same running within Cisco IOS XE as they would be in a traditional
Cisco IOS release. You may determine exactly which Cisco IOS Release 15 image
that the IOS daemon is using by issuing a "show version running" on
the console or by simply looking at the filename of the image.
Q. What is
Cisco's long-term commitment to Cisco IOS XE?
A. Most next-generation
platforms will be migrating to Cisco IOS XE over the coming months and years.
Q. Will my
current switches and routers be upgraded to Cisco IOS XE?
A. No, in an
effort to simplify the transition, Cisco IOS XE will only be introduced as new
generations of hardware platforms are released. No in-service upgrade of an
existing platform will be provided. Similarly, any platform that runs Cisco IOS
XE will not support running Cisco IOS.
Q. How will
features be shared between IOS and IOS XE?
A. Since
Cisco IOS XE contains Cisco IOS within itself as IOSd, all features created
within IOS will also appear in IOS XE and vice versa. Only new integrated
services and functionality created outside of IOSd will not be shared with a
Cisco IOS release. However, these integrated services may be introduced on a
Cisco IOS platform through the use of Integrated Services daughter cards which
will be available on a platform by platform basis.
Q. What
services will be provided on Cisco IOS XE, and how open will this platform be
to integrated third-party services and applications?
A. Services
that were traditionally managed by standalone appliances or servers will now be
integrated into the Cisco IOS XE environment. Examples today include Cisco
Unified Border Element (CUBE) and Session Border Controller (SBC), but this
will evolve over time.
Cisco
IOS XE Software Package Compatibility for ISSU
When upgrading the Cisco IOS XE
operating system software using the In Service Software Upgrade
(ISSU) process, it is important
to determine the compatibility of the upgraded software to your current software and hardware. The ISSU
process allows software to be updated or otherwise modified while packet forwarding continues with
minimal interruption.
Cisco IOS XE
release compatibility using the ISSU process utilizes the SSO functionality to
preserve
state while
software versions on the router differ, as during an upgrade. Most SSO-capable
features in
each Cisco IOS
XE release are ISSU capable. ISSU is only supported if SSO is enabled in the configuration
and the system is in a steady state (SSO ready state has been achieved). ISSU
compatibility depends on the set of specific feature clients that are in use
and whether they support ISSU. All ISSU upgrades include at least one IOS
switchover operation. It is important to understand which features are in use
and whether these features are ISSU compatible.
The Cisco
ASR1006 Series Router is a hardware-redundant chassis. The hardware-redundant
chassis hastwo ESP line
cards and two RPs which exchange state using hardware links. The Cisco ASR1002
andASR1004 Series
Routers are not hardware redundant, but are software-redundancy capable. The
non-redundant
chassis has a single RP and a single ESP, but allows the operation of up to two
IOS
processes on the
single RP to exchange states locally.
• Non-hardware-redundant
chassis models (such as the Cisco ASR 1002 Router and Cisco ASR 1004
Router)—Supports ISSU only if the
router is running in subpackage mode.
• Hardware-redundant
chassis models (such as the Cisco ASR 1006 Router)—Supports ISSU when
the router is running in
sub-package mode or in consolidated package mode.
For a complete discussion about
the ISSU upgrade process on the Cisco ASR 1000 Series Routers,including
prerequisites and restrictions, see the “In Service Software Upgrade (ISSU)”
chapter of the Cisco ASR 1000 Series Aggregation Services Software
Configuration Guide.
Reference: Cisco
Improved
performance—CEF is less CPU-intensive than fast switching route
caching. More CPU processing power can be dedicated to Layer 3 services
such as quality of service (QoS) and encryption. 
