What is the key difference between IOS, IOS-XE and IOS XR for cisco devices ?

IOS

The classical IOS is a monolithic kernel that runs all of the necessary modules in the same memory space. This means that if something happens to the routing engine or the LED indicator, it can cause the whole IOS kernel to crash if it runs out of memory. That may have been okay years ago but today’s mission critical networks can’t afford to have a rogue process bringing down an entire chassis switch.

To resolve above issue Cisco’s software engineers, rebuild the IOS CLI on a more robust platform known as IOS-XE

 

IOS-XE 

IOS XE runs as a system daemon on a “modern Linux platform.”  Cisco also abstracted the system functions out of the main kernel and into separate processes. That means that if one of them goes belly up it won’t take the core kernel with it. One of the other benefits of running the kernel as a system daemon is that you can now balance the workload of the processes across multiple processor cores.

 

IOS-XR

IOS XR is what the Mirror Universe version of IOS would look like. Much like IOS XE, IOS XR does away with the monolithic kernel and shared memory space of IOS Classic. XR uses an OS from QNX to serve as the base for the IOS functions. XR also segments the ancillary process in IOS into separate memory spaces to prevent system crashes from an errant bug. XR is aimed at the larger service provider platforms like the ASR and CRS series of routers. You can see that in the way that XR can allow multiple routing protocol processes to be executed at the same time in different memory spaces. That’s a big key to the service provider.

What makes IOS XR so different from IOS Classic? That lies in the configuration method. While the CLI may resemble the IOS that you’re used to, Instead of making live config changes on a live system, the running configuration is forked into a separate memory space. Once you have created all the changes that you need to make, you have to perform a sanity check on the config before it can be moved into live production.

 

 Hope this answers your queries 

 

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 XE is a software available for the ASR1K. In fact, in my point of view, it’s like having a Linux with a IOS interface. All the IOS functions are provided by a daemon called IOSD. It is the same interface that the IOS with some minor changes like on the debugs… You could even have access to the Linux interface by typing :

request platform software system shell r0

A good book to start with IOS XE is Building Service-Aware Networks written by Muhammad Afaq Khan.

Hi, Can you suggest the Entry level model# for both the OS - IOS-XR and IOS-XE in Cisco With routing protocol support like bgp and ospf

IOS XE is a software available for the ASR1K. In fact, in my point of view, it’s like having a Linux with a IOS interface. All the IOS functions are provided by a daemon called IOSD. It is the same interface that the IOS with some minor changes like on the debugs.

A good book to start with IOS XE is Building Service-Aware Networks written by Muhammad Afaq Khan.

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.

To start with IOS XR, I recommended Cisco IOS XR Fundamentals by Mobeen Tahir, Mark Ghattas, Dawit Birhanu et Syed Natif Nawaz.

Cisco IOS is a software based platform used to maintain LAN/WAN and telecommunications functions on various Cisco networking devices

Cisco IOS XE OS - Enchanced version of IOS which has same CLI syntax as IOS. It provides better HA for consistent Network services even with critical network conditions. Multi-core CPUs and SMP, Seperate Control and Data plane, facilitates programmability for cloud services.

Cisco IOS XR OS runs on a number of Cisco's large, service-provider focused platforms. Many of the commands, syntax, and management interfaces for IOS XR are quite different than the other major IOS. Works as distributed OS to provide modularity and memory protection between processes.

IOS XR is a realtime Internetwork Operating System designed for Cisco's high-end carrier routing platforms such as the CNS-1 and the 12000. IOS XE, on the other hand, is a modular IOS architecture designed for the Cisco ASR platform.