Working 3745 IOS download for Gns3
IOS image is software or Operating System used in most Cisco routers and switches. IOS images support different packages like routing, switching, and inter-networking, etc. You can use these IOS images with GNS3. Gns3 is one of the famous network simulators and its hot feature is that it can run the real Cisco IOS image, as compared to another network simulator like packet-tracer which performs all functions based on programming. If you are a beginner then learn more here:Cisco Switch Basic Configuration, how to use or configure GNS3
Remember only the c7200 series ios images get newer IOS images. According to Cisco, all other platforms are now “end of life”, but you can use these older ios images as well with Gns3.
Gns3 3745 IOS image Details
Cisco 3700 Series are the multi-service routers that provide LAN/WAN connectivity, new high-density service modules, and support for multiple advanced integration modules. You can use the NM-16ESW module with this 3745 IOS, which will enable the switching functionality in GNS3. In this way you will be able to perform different switching labs with GNS3 like Vlans, inter-VLAN (Router on a stick), VTP (VLAN trunking protocol), different multi-layer functionality, etc. learn more about Layer 3 Switching vs Routing
From here you can download the Cisco 3745 IOS image for your GNS3 and perform different GNS3 labs with this IOS. Remember this IOS is only for informational, practice purposes, and for GNS3 used. If you need the IOS for your real hardware then it is better to Contact Cisco for the latest and best IOS for your device. Following are the details and recommended setting of Gns3 3745 IOS image for your GNS3 setup. This Image was tested with Gns3 1.1 and i hope this will also work fine with the latest GNS3 version as well.
IOS version =12.4.25d (Mainline)
File name: c3745-adventerprisek9-mz.124-25d.bin
Minimum RAM: 128 but alteast 256MB recommended
Best idle-PC value: 0x60aa1da0, you can set other idle PC values as well
Here is the link from where you can download IOS for your Gns3