Cisco Router IOS XR Bedienungsanleitung PDF herunterladen (Seite 4)

Cisco IOS XR Training Page 4

1. Cisco IOS XR Introduction and

Comparison to IOS

Let’s start with the basic difference between Cisco IOS and Cisco IOS XR

code, the Operating System.

In Cisco IOS, the kernel is monolithic, meaning everything in installed in a

single image and all processes share the same address space. There is no

memory protection between processes, so if one crashes it can impact all

other processes on the box – thus forcing or causing a reload of the entire

router. The other thing with monolithic code is that it has a run to

completion scheduler, so the kernel will not preempt a process that is

running; the process must make a kernel call before another process has a

chance to execute.

In Cisco IOS XR, the kernel is based on an OS called QNX Neutrino that runs

some very powerful and reliable systems. QNX runs – per their News Release at

http://www.qnx.com/news/pr_1329_3.html - things from EKG machines, to Air

Traffic Control systems, and among other things – automated beer bottle

inspection systems. IOS XR offers modularity and memory protection between

processes, threads and supports preemptive scheduling as well as the ability

to restart a failed process. Protocols like BGP, OSPF, OSPFv3, RIBv4, RIBv6,

etc all run in separate spaces – if one has a fault, it will not impact the

others. Also, an added bonus, if you run multiple routing protocol instances

(like OSPF), each process will run in its own memory space – this is an

important feature of Service Providers – any fault with one customer process

will not impact another.

Another big difference between IOS and IOS XR is the configuration model. IOS

is a single stage model meaning that as soon as you make a change, it is

applied to the active running config. With IOS XR, you have a running

(active) config that you cannot modify directly, all your changes are made in

a staging area first before being committed to the running config. After you

make your changes, you commit them and promote the staging config to the

active config. Before the change is made active, the IOS XR will run a sanity

check on it making sure that the commands are correct to a certain degree, if

there is a problem it will tell you so that you can correct the error

% Failed to commit one or more configuration items. Please use 'show configuration failed' to view the

errors

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