Cisco IOS 12.4 vs 15.1

[GuoPatrick02]

Hey, I heard that IOS 15 is basically 12 with more features. Are all the commands still the same or are there changes in the command structures for certain parts?

[Pulikkal Sekharan Raju]

Hi Patrick,

This is a higher version of IOS code. There can be slight change in some command syntax. Otherwise syntax is going to be same like in 12.4.

http://www.cisco.com/en/US/prod/collateral/iosswrel/ps8802/ps10587/ps10591/ps10621/qa_c67_561940.html

Thanks

Raju

[GuoPatrick02]

Ehh I was lookin more towards if "I could use 15.1 IOS to study for the CCIE lab exam"

[Pulikkal Sekharan Raju]

You can use 15.1 for practicing.  But if possible try to use 12.4 itslef so that you don't practice some new commands which is supported in 15.1 but not in 12.4

Thanks

Raju

[GuoPatrick02]

Ehh I'm kinda confused. Do you know that there's some differences or is that what you think? Somebody told me that IOS 15 and 12 are the same commands its just that 15 has a few new features. Not saying I disagree or anything but I just want accurate information

[Pulikkal Sekharan Raju · Accepted solution]

That is true. Same commands will work

I am talking about the new features only. Just make sure that you practice only commands which is present in 12.4.

Chances are very less of using commands which are not supported in 12.4. Just mentioend that rare risk for you to be aware.

If you just practice only referring 12.4 command line there is no issues

Thanks

Raju

[GuoPatrick02]

OHH lol I thought you were talkin about old commands too. Thanks for the answers

[Pulikkal Sekharan Raju]

You are welcome

[mohamedjasren]

hi Rajs, just want to add on ask. how about 2811, migration from 12.4T to 15.1 can be direct? any configuration need to be change? thanks

[Joseph W. Doherty]

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Posting

Patrick Guo wrote:
Hey, I heard that IOS 15 is basically 12 with more features. Are all the commands still the same or are there changes in the command structures for certain parts?

Yup, generally newer IOS versions add new commands or command options, however . . .

As the other posts have noted, almost always, newer IOS versions support the commands in prior IOS versions.  Very rarely, commands are removed.  A little less than very rarely, commands are renamed.  (Note: often an IOS upgrade will automatically rename such commands.  An IOS downgrade, though, can require manual command re-application of renamed commands.)  Sometimes, and also generally rare, defaults will change for commands.  (I.e. going from one IOS version to another, a command may "appear" or "disappear" from the config.)  Lastly, also and very, very rarely, the same command might work just a little bit differently between IOS versions.

PS:

BTW, if you use 12.4T, it will be much like 15.0.