IOS Upgrade

[Michael Maxwell]

I am looking to upgrade my company swicthes which consist of 29601's and 3750's. When I upgrade the IOS will it have any effect on the existing config or will it just over write the IOS version.

Thanks

[Reza Sharifi]

see the other post.

[Richard Burts]

Without knowing what version you are currently running and what version you will upgrade to it is difficult to answer your question exactly. But we can say that in general a code upgrade just changes the operating version with little impact on the config. There are sometimes some new commands introduced in the new version which will appear in the config. There are (rarely) some changes in command syntax and (even more rarely) some command may be deprecated and stop working. So the best advice is to read carefully the release notes of the version you are upgrading to. The release notes will usually identify anything in the version that impacts the configuration.

My final comment is that Cisco works hard to make sure that new versions are backward compatible (config commands from old versions should still work in the new version) and so upgrades frequently do not impact the config in a way that you would notice. But there are occasionally version upgrades that do impact the config and so you need to read release notes carefully.

HTH

Rick

[Michael Maxwell]

Thanks Rick

I will look into it.

[Joseph W. Doherty]

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Posting

As Rick notes, upgrading an IOS version usually has no adverse impact to an existing config, although some configuration statements might have different syntax.  (On many later devices, after you boot into a newer IOS, you might try the command sh arc con dif nvram:startup-config system:running-config.  If the command is accepted, it will show differences between the startup config and the running config; which may differ because of a newer IOS version.)

Rarely, if you jump lots of versions during an upgrade, you might run into old syntax that the newer IOS cannot process.

Do be aware, that although newer IOS versions can usually process older IOS configs, the converse generally isn't true.  So if you upgrade, and decide you need to revert, you may need to remediate the config.  (When upgrading the IOS, you might want to save another copy of the startup config [in flash or elsewhere] to simplify IOS version reversion.)

[Michael Maxwell]

Thanks Joesph, I have current up to date backups of all the switch configs.

I will keep this in mind when I am going through the upgrade.

Thanks