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My colleague said that it is possible to virtualize a Cisco router i.e. run the Cisco IOS inside ESXi and it would act like a real cisco router so thus can be used in a light production environment.

I was a bit skeptical about this and have tried to Google it. I also found to a Cisco IOS XRv 9000 Router. Though I am still not clear I understand this.

Is it possible to actually virtualize a Cisco router as a VM to use it as a router in a network to do things like static route, RIP etc?

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The IOS XRv 9000 is probably a bit of an oddball - it's IOS-XR based. I never got round to get my hands on it or any other device running IOS-XR. That's carrier and service provider grade stuff, and my CCNA/CCNP SP career never quite took off.

You're probably looking for the Cisco CSR1000V, and yes, that's a perfectly "normal" IOS-XE based router in a VM shell.

It needs to be licensed by feature sets and desired throughput levels (from 10M to 10G). I comes in Xen, Hyper-V, KVM, ESXi and even AWS flavours, and has up to 8 virtual interfaces/vNICs, each of which can be run with 802.1q tagging, if the underlying hypervisor allows for it. It can do VRF-lite, MPLS, NAT, WaaS, QoS, IPSec, runs any routing protocol IOS-XE supports and can do ... possibly anything you can do with IOS-XE that does not require special hardware features. And none of these things need to be "lightweight".

IOS on an IOS-XE based router (such as the ISR4000 series) is nothing much more than an IOS environment on a well-hidden hypervisor. So why not run it on someone else's hypervisor, too?

I've been using CSR1000vs for uses cases like:

  • Router based CA for running a FlexVPN/IKEv2-DMVPN-alike IPSec WAN overlay with certificate authentication
  • internal-BGP route reflector for MPLS-VPN setups
  • FlexVPN Client to connect to financial service providers (instead of housing yet another 890 series)
  • or just a simple IPsec VPN peer for various needs of site-to-site connectivity
  • experimenting with IPv6 and NAT64
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  • Thank you for the answer, it provided me more information to look into. Oct 30 '18 at 3:32
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Yes, many vendors of networking equipment offer virtual alternatives nowadays for their physical hardware. It allows you to use the full power and featureset of a real networking device (a switch, router, firewall or load balancer for example) within virtualized environments.

You can also run them on a dedicated hypervisor for more performance. Especially if you're able to use techniques like SR-IOV you're able to reach quite decent performance up to several gigabits/sec depending on the physical hardware used.

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Traditional IOS can be run on "simulated" hardware -- GNS3, dynamips, etc. But it's a pretty poor approximation of the real hardware.

More modern incarnations of IOS-XE/IOS-XR/NX-OS are Linux with an "IOSd" as a process / container. (You can actually run other software along side IOS on such platforms.) And then there's the virtual router lab's IOS; this is what Cisco uses internally for training labs.

So, yes, it can, but short of sneaking VIRL out of Cisco, it's not as simple as deploying an ova.

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  • Yes, it can be as simple as deploying an ova, because an ova is what you get when you download the ESXi flavour of a CSR1000V. Having a suitable service contract with Cisco may be necessary, much less of an obstacle than sneaking VIRL out of Cisco. Oct 25 '18 at 9:07

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