Dhiman
There are several aspects to take into account when choosing an image file for a router. You must know how much memory to run the code and how much flash to store the image are available in the router. Various versions would have different requirements for memory and for flash. You would also need to consider which feature set you need. There are basic feature sets (like IP only) which give you basic router functions and there are more advanced feature sets which give other functionality such as the ability to support encryption, or to to firewall style filtering. If you could tell us how much memory and flash are available and what set of features you need then we could help to identify versions for you.
Your question asked about the latest IOS. According to the Feature Navigator on the Cisco site the latest version for 3620 is 12.3(24a) and a version implementing IP feature set would be c3620-i-mz.123-24a.bin.
Or if you were really looking for the most recent in the 12.0 version it would be 12.0(28d). And the image with the IP only feature set would be c3620-i-mz.120-28d.bin.
You can find more of this information at www.cisco.com/go/fn
HTH
Rick
HTH
Rick
