Home > AAA TACACS+ and RADIUS Tutorial


October 18th, 2018 Go to comments

AAA Configuration

The following steps are required to configure AAA:

1. Enable the “new model” of AAA.
2. Configure the server(s) to be used for AAA (e.g. TACACS+ or RADIUS servers).
3. Define authentication and authorization method lists.
4. Enforce AAA authentication on the relevant lines (e.g. console and VTY lines).


In this example we will do an Authentication configuration so that the users are authenticated when telnet to the device:

1. Globally enables AAA on a device:

Switch(config)#aaa new-model

2. We are going to configure the server to be used for AAA and the key; note that the key used is the same key that was configured on the RADIUS server.

Switch(config)#radius-server host key MySecretP@ssword

In the above command we don’t specify the ports used for RADIUS authentication and accounting so it will use the default values of 1645 and 1646, respectively (or we can specify them via the “radius-server host auth-port 1645 acct-port 1646 key MySecretP@ssword” command). The full syntax of above command is:

Switch(config)# radius-server host { hostname | ip-address } [ auth-port port-number ] [ acct-port port-number ] [ timeout seconds ] [ retransmit retries ] [ key string] [alias {hostname | ip address}]

3. We will activate authentication for logins to the device and specify that RADIUS is the preferred method but we should include the local user database as a fall back if RADIUS becomes unavailable. Note that users in the local database cannot be used if the user doesn’t exist in RADIUS, it will only fall back if the RADIUS server is offline.

Switch(config)#aaa authentication login default group radius local

This command is broken down as follows:

+ The ‘aaa authentication’ part is simply saying we want to configure authentication settings.
+ The ‘login’ is stating that we want to prompt for a username/password when a connection is made to the device.
+ The ‘default’ means we want to apply for all login connections (such as tty, vty, console and aux). If we use this keyword, we don’t need to configure anything else under tty, vty and aux lines. If we don’t use this keyword then we have to specify which line(s) we want to apply the authentication feature. An example of not using the ‘default’ keyword is shown in step 4 below.
+ The ‘group radius local” means all users are authenticated using RADIUS servers (the first method). If the RADIUS servers don’t respond (unreachable), then the router’s local database is used (the second method). But notice that if the RADIUS server is reachable while the user has not configured on it, it will not fallback and try to search in the local database. It will display% Authentication failed message.

Note: If we don’t have the ‘local’ keyword (only ‘aaa authentication login default group radius’ command then the authentication will fail if the AAA server does not reply to the authentication request as there is no fallback authentication method)

For local authentication to work we need to create a local user. To create a new user, with password stored in plain text:

Switch(config)#username User1 password CCNA_cisco

But having passwords in plain text isn’t a good idea! The below command is better to create a new user, with password stored in encrypted text:

Switch(config)#username test2 secret Pa55w0rd

specify the RADIUS server and a group to be used.

4. In step 3, if we don’t use the ‘default’ login method list, for example:

Switch(config)#aaa authentication login MY_AUTHEN_GROUP group radius local

Then we have to configure the same group (MY_AUTHEN_GROUP in this case) to the specific line(s) with the “login authentication list_name” command. For example we want to apply to VTY lines (for telnet):

Switch(config)#line vty 0 4
Switch(config)# login authentication MY_AUTHEN_GROUP

+ We can configure different usernames/passwords on the local device and the remote AAA server but for normal users we should configure same usernames/passwords on both devices so that the transition (in case the remote AAA server fails) is transparent to them.
+ Use the aaa authentication global configuration command to define method lists for RADIUS authentication
+ Use the aaa authorization global command to authorize specific user functions
+ Use the aaa accounting command to enable accounting for RADIUS connections

So in conclusion this is all the config we need for a simple authentication using AAA:

Switch(config)#username test2 secret Pa55w0rd
Switch(config)#aaa new-model
Switch(config)#radius-server host key MySecretP@ssword
Switch(config)#aaa authentication login MY_AUTHEN_GROUP group radius local
Switch(config)#line vty 0 4
Switch(config)# login authentication MY_AUTHEN_GROUP

A simple TACACS+ configuration for authentication would be:

aaa new-model
aaa authentication login default group tacacs+ local
tacacs-server host
tacacs-server key login@pass!

With this configured, when logging in, the password supplied will be attempted to be verified by the TACACS+ server before access is granted. If the server is unavailable/unreachable, then the switch will fall back to using the local authentication database.

In the next part we will see some examples of configuring AAA.

Comments (18) Comments
Comment pages
1 2 4228
  1. Eddie
    May 15th, 2019

    I’m sitting for the 200-125 next week…any valid dumps?thanks

  2. derere
    May 22nd, 2019

    im not a robot

  3. Aitizaz
    May 25th, 2019

    Hi, Anyone have idea? From where can I get IBM QRadar SIEM C2150-624 dumps for free?

  4. Intan faudi
    May 30th, 2019

    i hope you all has last dump for ccna 200-125 pls send to {email not allowed}

  5. Anonymous
    May 31st, 2019

    please anyone send me latest dump for the 200-125 to primmk (at) gmail (dot) com

    June 1st, 2019

    I want to be a membership of this site

  7. a2
    June 7th, 2019


  8. TonyS
    June 9th, 2019

    Please if someone has the latest dumps can you send me to the next :

  9. Pat
    June 10th, 2019

    Can anyone please assist me with latest dump for ccna.. Taking the exam very soon.. Pls send to my mail pat2mail2000 (at) yahoo (dot) com

  10. Tope
    June 14th, 2019

    Anyone with latest ccna dumps should please help me out.I am writing 200-125 next week. Help me send it to {email not allowed}k you.

  11. Joe
    June 14th, 2019

    Please,help with latest ccna 200-125 dumps. Send to idkan1atyahoodotcom

  12. maheen
    June 22nd, 2019

    please can someone send me 200-125 latest dumbs as soon as possible .my email address is {email not allowed}.

  13. nickojam
    June 23rd, 2019

    please.. i failed in my first ccna 200-125 exam. Exam fee is difficult in my situation.. I will retake exam soon.. please to whom kind hearted, help me with the latest dumps.. {email not allowed}

  14. nickojam
    June 23rd, 2019

    please.. i failed in my first ccna 200-125 exam. Exam fee is difficult in my situation.. I will retake exam soon.. please to whom kind hearted, help me with the latest dumps.. nickojamkoh2914 (at) gmail.com

  15. Sir
    June 28th, 2019

    I have updated dumps after recent exam changes.
    Get at below: pass on first attempt.


  16. Shukran
    June 29th, 2019

    Please send me actual dumps> shukran68346 @ gmail . com <thank you for all

  17. pankos
    July 15th, 2019

    Hello, can anyone send me latest dumps? kosioka(at)gmail.com Thank You.

  18. Jawaid
    July 18th, 2019

    Hi, can anyone send me CCNA 200-125 latest dumps at m.jawaid(at)outlook.com Thank You.

Comment pages
1 2 4228
Add a Comment