Routing for the future: Cisco ASR IOS XE

Cisco’s ASR routers gives a new Edge to the Routing technologies that exist today. It introduces the new concept of distributed software components for routers to make them more resilient.

source: NetworkWorld

You can search for “IOS XE” and get plenty of results or you could click around a lot and finally find it, but that’s wrong. XE is a key component of the ASR line and it should be easy to find and review. It almost appears Cisco is hiding the information or, at a minimum, just trying to say it’s IOS, whereas NX-OS is different and gets its own support sections. I disagree; IOS XE is different and should be made clearly available.

Nowhere on the ASR main page is a link – or for that matter even the letters “XE” – to XE material. It’s there, under “All support information for Cisco ASR 1000 Series Aggregation Services Routers”, but it’s certainly not a highlighted part of the ASR material.

IOS XE is a “distributed software architecture that moves many operating system responsibilities out of the IOS process”. Whereas in traditional software IOS controlled almost everything, in XE IOS is just one of twelve processes. This separates responsibility for the operation of the router into distinct modules that have isolated fault domains. So, if something goes wrong in the “Logger” process, it won’t crash the “IOS” process.

The actual IOS XE software comes in seven individual sub-packages (files) which are combined into a complete consolidated package (file). 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. So, if you want a screaming, kick-butt ASR, you’ll need to load individual sub-packages, not a complete consolidated package (file).

Once the router is booted and running, the CLI is “identical in look, feel, and usage to the Cisco IOS CLI on most platforms.” As best I can tell, it’s IOS version 12.2(33)XN-series code.

One other nice feature of IOS XE is that is can run two IOS processes on a single RP. The 1002 and 1004 versions do not allow dual, physical RPs, so, instead, you can configure two IOS processes on the same RP. That way, should the IOS process hit a bug and fail, the backup IOS process takes over. This does not protect against hardware failures, but can provide protection against the more likely failure: software bugs.

One final note about In Service Software Upgrade (ISSU). ISSU is a very nice feature that can help prevent any outages during upgrades, but it’s not a simple decision to upgrade from one version to any other version. ISSU has strict IOS XE version compatibility steps that must be adhered to or the upgrade could interrupt traffic. You may have to do two upgrades if you want to use ISSU to get from your current version to your target version of IOS XE.

Overall, there are some very nice features in IOS XE. It’s definitely new so expect some bumps, but Cisco has setup XE as a platform for modularity. I would expect many (all?) router lines to be running IOS XE in the future.


http://cisco.com/en/US/products/ps9587/tsd_products_support_series_home.html“>Cisco IOS XE Main Support Page

Cisco ASR 1000 Series Aggregation Services Routers Software Configuration Guide

Cisco IOS XE Software End-of-Life Strategy

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