I wanted to cehck out difference between the Cisco ASR 1001 vs Cisco ASR 1001-X in terms of hardware limitations and licenses. Are both the routers IWAN capable?
If they are IWAN capable what feature differences do they have as compared to the Cisco 4xxx series?
This is not my main area ..
But the 1001-X is a refreshed 1001. So you should only be buying the 1001-X for new deployments. Both are iWAN capable.
They have greater performance than the 4000 series routers. They also cost a lot more.
So if money is no object, I guess look at the ASR 1001-X. If a 4000 series router has enough performance to do the job, you should take that option (as it is much cheaper). If you can't find a 4000 series router with enough throughput for your job then start looking at the ASR series.
Typically the 4000 series is more used by corporates, and the ASR series is more used by service providers.
As Phillip notes, ASR-1001-Xs have greater performance than a 4K ISR, especially if you've licensed the "faster" performance settings (one of the features of the -X, multiple levels of performance based on license). This is important if you need to support multiple gig or 10g interfaces.
And as Phillip also noted, they also cost a lot more.
As to 4Ks being used by corporations and ASRs by service providers, that might have more do to with performance needs. Within an business, especially those not huge, you don't often have need for routers with multi-gig to 10g performance levels, for such, you're more likely to use a L3 switch.