Technically, IOL images were originally intended for internal Cisco use and for authorized partners.
The adventerprisek9 package includes:
This is a Layer 3 (Router) image. While it supports routing protocols, it often includes switching features that standard Dynamips router images lack. i86bi-linux-l3-adventerprisek9-15.4.2t.bin
: While newer than the 12.4 era, 15.4(2)T is considered highly stable for lab environments and certification preparation (e.g., CCNP or CCIE). CCNP or CCIE).