Need help upgrading from 12.4(13r)T

[dfclin073]

For security reasons I would like to upgrading my Cisco 3825 router from 12.4(13r)T to 15.1.4M12a.  Does 15.1.4M12a have any dependencies going from 12.4 to 15.1? Or can I upgrade directly?

Thank you,

Dan

[Leo Laohoo]

As long as the router has the right amount of DRAM and Flash, direct upgrade is supported.
NOTE: Read the Release Notes prior to upgrade.
IOS version 15.1 is not a new or recent version. Are you sure this is the right IOS version to go to?

[dfclin073]

I believe it is the highest version the 3825 will support.

[Leo Laohoo]

Whao. I didn't realize it was that old.
Anyway, make sure you've got enough DRAM (512 mb) and flash (at least 128 mb).

[Joseph W. Doherty]

"Does 15.1.4M12a have any dependencies going from 12.4 to 15.1? Or can I upgrade directly?"

Probably not, which is the general case for ISRs. However, as Leo mentions, it's suggested to review the release notes.

Sometimes, though, when jumping IOS versions, Cisco will change syntax for some commands.. If the version jump is large enough, old syntax will not be understood. (Again, normally not a problem unless it's a very large jump up, however, it can be a problem downgrading.)

You might also look whether there are any ROM upgrades too. In the later 2800 (and 3800?) series, for example, support was added for booting from USB sticks. ROM release notes will document what's been changed.

[Leo Laohoo]

---

@Joseph W. Doherty wrote:
In the later 2800 (and 3800?) series, for example, support was added for booting from USB sticks.

---

Requires a ROMmon upgrade to enable boot using USB.

[Joseph W. Doherty]

"Requires a ROMmon upgrade to enable boot using USB."

Exactly! Leo, thanks for that, as my third paragraph may have been unclear as I only used the term "ROM' upgrade.