IOS Upgrade recommendation

Unanswered Question
Jul 28th, 2009

I have a 2801 router VPN Router with IOS c2801-advsecurityk9-mz.124-25a.bin installed which works fine. I have tried to upgrade to a .T version,but get poor performance. I have 384mb DRAM in this router, can someone recommend a flavour of 12.4T that will make the performance better, but still has crypto etc.


I have this problem too.
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Peter Paluch Tue, 07/28/2009 - 07:19


Unless you have a specific reason, I do not recommend upgrading to a T version of IOS. The T-train is a testing version of IOS in which new features and functions are implemented and tested and that will eventually become the new mainline version. However, because it contains new code that might contain several bugs and problems, it is not recommended to use it in a production network unless you absolutely need a feature that is not available in older IOSes.

Sorry if I disappointed you. The obvious rule here is that "newer" does not necessarily mean "better".

In any case, visit the following URL:

This tool is called Cisco Feature Navigator and you can use it to review many IOS versions and feature sets and find out which versions are there to suit you.

Best regards,


Edison Ortiz Tue, 07/28/2009 - 13:32


While I agree with Peter that Mainline is the recommended choice when installing an IOS on a router, I've been recommending 12.4(15)T over 12.4(25)M due to 12.4(15)T's maturity level.

12.4(15)T8 and 12.4(15)T9 have been very solid in terms of reliability.





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