The other day I was implementing BGP when I was presented, much to my horror, with a message stating that BGP was not available in this image.
Strange, because I had two identical routers, both the same model, and it worked fine on the other one! When I looked, one had and advancedIP image, and one had a baseIP image.
No problem, I thought. Set one up as a TFTP server, TFTP the image across and change the IOS. What could go wrong?
What could go wrong is this message:
Not enough memory in the system to run this image Required pmem/iomem: 39435385/524288 *** System received a Software forced crash ***
Turns out, my two "identical" routers aren't so identical. One had had a memory upgrade.
Anyway, all hail the Cisco Feature Navigator. It can be found at: http://tools.cisco.com/ITDIT/CFN/
If you select "Research Software", you can search by router model, software release, etc. You can even put in the filename of the image and find it.
It's pretty good. When you search for an image, you can find out exactly which features are supported in the image, how much flash memory you need, and how much DRAM.
Now if I'd had the foresight to do it before I jumped in head first, I wouldn't have had to spend the next hour in ROMMON mode recovering the router!