In the past I spun up JunOS Olive in my home lab to learn JunOS.
But it looks like Juniper has something called vMX. Is this comparable to vMX?
Obviously its not free, but for learning purposes (learn juniper routers and switches) would vMX be the same or even better than Olive?
Junos Olive is an unofficial and unsupported image/version that was developed by Juniper for development purposes.
As for the vMX, it's "a full-featured, virtualized MX Series 3D Universal Edge Router" (quote from Juniper). It's an official and supported product that allows the usage of a virtualized MX router in a cloud/virtual network environment. As such, all the features/commands that are available for a physical MX router are available in vMX.
Junos Olive was never built to be a fully working version while vMX was. If you need some of the missing features from Olive (or a more updated version of Junos), vMX is a good solution (but you'll need an hypervisor to install it). Otherwise Olive should be good enough.
Olive will not have a data-plane... as a matter of fact if you watch an Olive boot, it will look identical to an MX or M/T series that has the switch-fabric boards removed as they will all boot into "olive mode" meaning 'dataplane-less' Junos routing-engine.
All those factoids aside, what it means for someone that is trying lab exercises is that things like the following will have limited or no functionality: - Any form of traffic encapsulations (GRE, IPoIP, IPSec, etc) will not be supported as dataplane resources are required to perform these encap/decap functions - Class-of-service: there's no switching fabric and are no PFEs, therefore no queues, schedulers, etc. therefore no CoS. - Security services: This is more of a function of vSRX than vMX, but again, all security services would not be present in Olive as there's no FWDD to support it/them. - Multicast: since multicast replcication is handled in the dataplane, mcast functionality is limited in it's realism though it is working in Olive. For example: for OSPF study, mcast functionality in Olive is there, but if you're looking to model realism in mcast data-plane, it's not there.
Control-plane functionality is all there. So if you're looking to study for any JNCIA/JNCIS/JNCIP, Olive will be very useful but keep in mind that vMX, vSRX and vQFX all have evaluation licenses that with a simple VM snapshot that both ESXi and KVM support, you can extend the longevity of that license with relatively little additional hassle and you've got the latest version of Junos to work with and full feature sets.
These are the things I can think of off the top of my head but you can google "Olive Juniperclue" and I believe there's a more complete list of what does/doesn't work there but hope this helps!
As for GNS3: while I can’t speak first-hand on the limitation you mention, another option would always be that you can always run vMX versions newer than 14.1 as a stand-alone VM with bridged interfaces and use a bridge cloud in your GNS3 topology to create a unified broadcast domain between interfaces inside your GNS3 topo and devices running outside of it.
If you use GNS3 network simulator to run vMX: Use versions 14.1R4.8 (or older). Starting with 15.1, vMX was split into two VMs and no longer works with GNS3.
