Any AAA configuration on a Cisco router begins with the command aaa new-model. Per the context help:

R1(config)#aaa ?
  new-model       Enable NEW access control commands and functions.(Disables OLD commands.)

What were the old commands? What major difference where there between the old commands and what you get with the new commands?

  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer. – Ron Maupin Aug 12 '17 at 18:54

Basically, the old model was just Authentication with little Authorization and no real Accounting. Maybe you just call it A instead of AAA. :)

Searching the Internet has turned up a few references:

From Cisco Tips and Tricks:

Historically older methods of AAA have revolved around line level passwords and secrets. This leveraged user set passwords on the various access points around the router to stop someone from directly logging onto the device and making changes.

aaa new-model

This will turn the engine on and immediately overwrite/remove all line level passwords and old methods of authentication. With this in mind, if you lose connection to this router at any stage you will not be able to get back on as there will be no rules to govern the Auth part of the AAA and the default is to allow no access unless configured to allow "no auth". (a simple reboot will however return you to the old setup as the command requires the usual saves)

From Free CCNA Workbook:

When configuring AAA New-model, authorization is not configured by default on newer IOS images therefore when logging into a Cisco Router and/or Switch with a user account that has level 15 privileges you will not automatically be placed into privileged mode as you were in the older non-aaa login local authentication method. To fix this you’ll need to add a AAA statement to specify console authorization.

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