If you just need to use the image (not download the file), Cisco offers free DevNet Sandboxes. You can reserve a lab environment containing this exact IOSv version for 2–4 hours.
: Represents the software version, in this case, Cisco IOS 15.6(2)T . How to use it in Network Labs
Downloading Cisco software requires following legal and technical guidelines to ensure stability and compliance. 1. Official Cisco Modeling Labs (CML)
While GNS3 has historically used the Cisco 7200 router emulator (Dynamips), modern topologies require modern images. The CSR 1000v (which uses this VIOS image) allows engineers to simulate current-generation routers that support SD-WAN, advanced NAT, and modern programmability features.
: The virtual disk format used by VMware and other hypervisors.