Tag Archives: 1.1a

1.1.a Describe basic software architecture differences between IOS and IOS XE

http://rdccie.wikidot.com/describe-basic-software-architecture-differences-between-ios

1.1.a (iii) Excluding specific platform’s architecture

  • Non-IOS applications can either be tightly integrated with IOS or they could run side-by-side with IOS with very little or no interactions
  • If an application does require services from IOS, it integrates with IOS through a set of client libraries called “service points”

1.1.a Describe basic software architecture differences between IOS and IOS XE

http://rdccie.wikidot.com/describe-basic-software-architecture-differences-between-ios

1.1.a (ii) Impact to troubleshooting and performances

  • IOS XE retains the exact same look and feel of IOS, provides enhanced future-proofing and improved functionality
  • IOS XE (IOS 15.0) runs as a single daemon within a Linux operating system
  • Additional system functions now run as additional, separate processes in the host OS environment
  • IOSd within the IOS XE environment supports multiple threads and multi-core CPUs
  • Wireshark and Mediatrace included, runs separately from IOS

1.1.a Describe basic software architecture differences between IOS and IOS XE

1.1.a [i] Control plane and Forwarding plane

IOS XE allows development of 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. It achieves 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. FFM programs the data plane via the FED and maintains forwarding state for the entire system. The FED is the instantiation of the hardware driver for the data plane.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 806-810).  . Kindle Edition.

1.1.a Describe basic software architecture differences between IOS and IOS XE

Cisco classic IOS has always had a monolithic software architecture, which means that it is both downloaded and run as a single binary image where all processes share the same memory address space. Monolithic and non-modular architecture leads to no memory protection between processes, as a result software defects in classic IOS code can potentially corrupt data used by other processes. It also has a run to completion scheduler, which means that the kernel does not preempt a running process — the process must make a kernel call before other processes can be scheduled and get a chance to run.

In all variations of classic Cisco IOS, packet routing and forwarding (switching) are distinct functions. Routing and other protocols run as IOS processes and contribute to the formation of Routing Information Base (RIB). 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-based forwarding (e.g., Cisco 7200 or Cisco ISR G2) most traffic handling is done at interrupt level using Cisco Express Forwarding (CEF). This helps avoid process context switching that would need to be done otherwise to forward packets. Routing functions such as OSPF or BGP run at the process level. In routers with hardware-based forwarding, such as the Cisco ASR1000 (which runs IOS XE) , ASR9000 or CRS-1 or NCS series (which run IOS XR), IOS computes the FIB in software running on route processor (RP) hardware (typically x86 CPUs) and loads it into the forwarding hardware (such as an ASIC or a network processor), which performs the actual packet forwarding function.

The IOS XE is a POSIX based environment along with various open source software 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 also includes a set of Cisco specific drivers and associated chassis/ platform management modules.

On top of the base operating system (Linux) and drivers , IOS XE provides a comprehensive set of infrastructure modules which define how software is installed , how processes are started and sequenced, how high-availability (HA) and software upgrades are performed. The core application that runs on top of this new infrastructure is the IOS feature set in the form of IOS daemon (IOSd). By running Cisco IOS, products reap the benefits of an extensive feature set for routing and switching platforms that has been built into IOS over last two decades.

Finally, the evolved IOS architecture is specifically designed to accommodate other applications outside of IOS blob or IOSd. These applications can be upgraded or restarted independently of IOSd. If an application does require services from IOS, it can integrate 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 is not a new network “OS” per se, it is rather an incarnation of classic IOS (“ IOS”) where role of classic IOS is reduced to an application running on top of a Linux kernel. This approach also allows building routing/ switching platforms that use a variety of data plane hardware (ASICs or network processors such as Cisco’s QFP or CPP) by way of the abstraction provided between control and data planes.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Location 804).  . Kindle Edition.

organization

in recent weeks i have taken to reorganizing this site to match the new v5 blueprint. the items categorized ccie v5 are all relevant to the blueprint. more specifically, those items tagged with 1.1a, 2.2.a etc, are an exact match to the blueprint, ie:

click the 1.1a  tag under between the sheets:

between the sheets

this will yield posts specifically aimed at satisfying the requirements for 1.1a for the ccie v5 written blueprint below:

Network theory
1.1.a Describe basic software architecture differences between IOS and IOS XE
1.1.a (i) Control plane and Forwarding plane
1.1.a (ii) Impact to troubleshooting and performances
1.1.a (iii) Excluding specific platform’s architecture

example_tag_1.1a

simple enough…