Cisco IOS , IOS- XE and IOS-XR

Currently there is three types of software on Cisco Routers. The classical IOS, the IOS XE and the IOS XR.

Cisco IOS :

Classical IOS is on the market for a long time. I start to work with IOS version 10 on Cisco 2500 routers. You will find this IOS on entry level routers like ISR or Enterprise switches like 6500 or 3750. This IOS is a monolythic OS. That means that all the features are in one file and if one function on the system fail most likely all the system fail. Also that mean that if you want to upgrade the Operating System, you need to reboot the system.

• 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, 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 actual IOS XE software comes in seven individual sub-packages (files) which are combined into a complete consolidated package (file).

ubPackage	Purpose
RPBase	Provides the operating system software for the Route Processor.
RPControl	Controls the control plane processes that interface between the IOS process and the rest of the platform.
RPAccess	Exports processing of restricted components, such as Secure Socket Layer (SSL), Secure Shell (SSH), and other security features.
RPIOS	Provides the Cisco IOS kernel, which is where IOS features are stored and run. Each consolidated package has a different RPIOS.
ESPBase	Provides the ESP operating system and control processes, and the ESP software.
SIPBase	Controls the SIP operating system and control processes.
SIPSPA	Provides the SPA driver and Field Programmable Device (FPD) images.

•  Cisco IOS XE Software Subpackage Functions:

1. RPBase:Provides the operating system software for the route processor
2. RPControl : Controls the control plane processes that interface between Cisco IOS Software and the rest of the platform
3. RPAccess : Provides software required for router access
4. RPIOS:  Provides the Cisco IOS Software kernel, which is where Cisco IOS Software features are stored and run; each consolidated package has a different RPIOS subpackage
5. ESPBase : Provides the ESP (Embedded Service Processor) operating system and control processes and the ESP software
6. SIPSPA : Provides the shared port adaptor (SPA) driver and associated field-programmable device (FPD) images
7. SIPBase : Controls the Session Initiation Protocol (SIP) carrier card operating system and control processes

• 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

Individual Processes

Process	Purpose	Affected FRUs	SubPackage Mapping
Chassis Manager	Responsible for all chassis management functions, including management of the HA state, environmental monitoring, and FRU state control.	RP (one instance per RP) SIP (one instance per SIP) ESP (one instance per ESP)	RPControl SIPBase ESPBase
Host Manager	Provides an interface between the IOS process and many of the information-gathering functions of the underlying platform kernel and operating system.	RP (one instance per RP) SIP (one instance per SIP) ESP (one instance per ESP)	RPControl SIPBase ESPBase
Logger	Provides IOS facing logging services to processes running on each FRU.	RP (one instance per RP) SIP (one instance per SIP) ESP (one instance per ESP)	RPControl SIPBase ESPBase
Interface Manager	Provides an interface between the IOS process and the per-SPA interface processes on the SIP.	RP (one instance per RP) SIP (one instance per SIP)	RPControl SIPBase
IOS	The IOS process implements all forwarding and routing features for the router.	RP (one per software redundancy instance per RP). Maximum of two instances per RP.	RPIOS
Forwarding Manager	Manages the downloading of configuration to each of the ESPs and the communication of forwarding plane information, such as statistics, to the IOS process.	RP (one per software redundancy instance per RP). Maximum of two instances per RP. ESP (one per ESP)	RPControl ESPBase
Pluggable Services	The integration point between platform policy application, such as authentication and the IOS process.	RP (one per software redundancy instance per RP). Maximum of two instances per RP.	RPControl
Shell Manager	Provides all user interface features and handling related to features in the nonIOS image of the consolidated package, which are also the features available in diagnostic mode when the IOS process fails.	RP (one instance per RP)	RPControl
SPA driver process	Provides an isolated process driver for a specific SPA.	SPA (one instance per SPA per SIP)	SIPSPA
CPP driver process	Manages the CPP hardware forwarding engine on the ESP.	ESP (one instance per ESP)	ESPBase
CPP HA process	Manages HA state for the CPP hardware forwarding engine.	ESP (one instance per ESP)	ESPBase
CPP SP process	Performs high-latency tasks for the CPP-facing functionality in the ESP instance of the Forwarding Manager process.	ESP (one instance per ESP)	ESPBase

Cisco IOS- XR:

IOS XR is a Carrier Class IOS, the goal is to provide a more stable solution with process mirroring and advanced features. The interface is really different from the classical IOS. For example when you do change on the configuration, you need to validate the changes with a “commit”. It is pretty good because you could multiple changes and the activate all the changes in one command. Also, that allow you to decide when the changes will be activated. And finally, you’ve got the option to roll back the changes. On the configuration side, instead of having the configuration grouped by interface, it is grouped by process… So you’ve got all together, the OSPF config or the PIM config, instead of having a part of the configuration on the interface and a part of the configuration at the process level.