Are you trying to into a specific simulator (like EVE-NG)?
For those seeking a legal way to practice, Cisco Modeling Labs (CML) is the official platform that provides sanctioned virtual images (vIOS) that offer similar functionality. i86bilinuxl3adventerprisek9m21573may2018bin
Cisco IOL/IOU images are proprietary. They are not officially released to the public and are generally intended for Cisco employees and authorized partners. Using them without a valid license from Cisco is technically a violation of their EULA. Are you trying to into a specific simulator (like EVE-NG)
: This is the standard file extension for a binary executable image. Significance in Network Engineering meaning the image supports routing functions.
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: Stands for Layer 3 , meaning the image supports routing functions.