refers to a 15.7(3)M release of Cisco IOS compiled specifically for an x86 Linux environment. This "IOU" (IOS on Unix) image is widely used by engineers to simulate complex Layer 3 routing features without needing expensive physical hardware. 2. Understanding the Filename Components
: This could be a version number or a build number. i86bilinuxl3adventerprisek9m21573may2018bin portable
i86-bilinux-l3-adventerprise-k9m-21573-may-2018-bin-portable refers to a 15
The term "portable" in your query likely refers to its use in portable lab environments i86bilinuxl3adventerprisek9m21573may2018bin portable