Cisco Support Community
Community Member

IOS 12.1(5)T VS. 12.1(5a)E2 o 7120'a & 7200's

I have two 7120's running IOS 12.1(5)T for IPSEC 3DES for VPN connectivity (PreShared Keys). I have been told that 12.1(5a)E2 resolves some issues for IPSEC, and 3DES. Although I haven't been having any problems, I'm about to add twice as many VPN's as I currently have and want to avoid any potential problems. I have searched and searched but have not found any documention on what additinal reliability or fixes were made for 12.1(5a)E2. Does anyone have any information ?

Community Member

Re: IOS 12.1(5)T VS. 12.1(5a)E2 o 7120'a & 7200's

12.1(5)T is listed in the IOS upgrade planner as a “Deferred Release” which is a version of code Cisco pulled due to major issues. For a better explanation, see

Prior to it’s Deferred status it was considered “Early Deployment” code as is 12.1(5a)E2. You have to run ED code to gain the features you want but expect issues. Once the code hits “General Deployment“ status, upgrade immediately as the code has been fairly stabilized by that point. You should have a good understanding of the code release designations. Look at for more information.

Lastly, you can use the Software Bug Toolkit on Cisco’s website to search for bugs filed against 12.1(5)T. Deferred release code will never be fixed but it will give you a good chance to use the tool and understand how it works.

CreatePlease to create content