Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
New Member

IOS versioning



I can't get a grip on the IOS versioning numbering.

Taking 12.2(44)SE3 as an example, (44) sould be maintainance number and the 3 of SE3 sould be the rebuild number. What is the difference beween these?

An higher maintainance number of a software train (i.e. 12.2SE) doesn't mean a 'newer' release.

For an 2960 version 12.2(58)SE2 seems te be older than 12.2(55)SE8.


Can someone plase explane?




Hi Dennis, SE, SE1,SE2....

Hi Dennis,


SE, SE1,SE2.... SE8, here numeric values defines the rebuild of the main version (SE).


12.2(44) SE3 is 12.2 Mainline (44th Maintenance Release) and Service Provider/Enterprise Trains (SE)'s 3rd Rebuild.

So recent one might be a older rebuild version with highest maintenance release.


Cisco rebuilds if they see so many bugs or defects in specific build..... they will rebuild once again and name it as SE2,3,4,..etc





New Member

Thanx Karthik. So if i want

Thanx Karthik.


So if i want the most recent IOS on my switches, should i download an image with the highest Maintainance Release or the one with the highest Rebuild Verion?

Hi Dennis, Once again it

Hi Dennis,


Once again it depends... but most recent we can say the highest rebuild version..... bcoz they go for rebuild version when they find more bugs on the previous versions or if they want to add additional features to it..... it is good to use the Cisco suggested versions..... There they will be updating the recent updates of the different rebuilds.....




Hall of Fame Super Gold

So if i want the most recent

So if i want the most recent IOS on my switches, should i download an image with the highest Maintainance Release or the one with the highest Rebuild Verion?

First of all, you need to test the IOS you've downloaded first (read between the lines).  


For the 3750-series family of switches, you can't beat the latest of the 12.2(55)SE line, 12.2(55)SE9, in stability.  2nd place goes to 15.0(2)SE4 (and only this specific version).  The rest is ... don't get me started.  

New Member

Thanks Leo,I've been

Thanks Leo,

I've been searching around and i've read indeed that the 12.2(55)SE line is the most stable one. Not only for the 3750 but also for 3560's and 2960's

Hall of Fame Super Gold

15.0(2)SE4 works very, very

15.0(2)SE4 works very, very well with me on my 2960/2960S and some 3560CG switches.  I'm currently testing 15.2(2)E on the 2960S and 3560CG.  So far, 15.2(2)E works well on the 2960S but not on the 3560CG.

Super Bronze

DisclaimerThe Author of this


The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.


Cisco often maintains multiple releases, concurrently.  That's why an "older" version/release, such as your 12.2(58)SE2 could have been released earlier than 12.2(55)SE8.  However, perhaps what's important is how "mature" a software train is.  In theory, 12.2(55)SE8 might be more "solid" than 12.2(58)SE2, not because it's released later, but because is the 8th "patch" vs. a 2nd "patch".  (Might not too, depends how "solid" the original release was too.)

Picking an IOS is usually best done by using the release that contains all your required features, and then using the latest release of that.  So, for example, if you didn't need (58) features, but both it and (55) have the features you need, you might run (55), again because it's been out longer and there's been (hopefully) more time for bugs to become known, and corrected.


CreatePlease to create content