Home > Articles > Certification > Cisco Certification > CCNP

This chapter is from the book

AAA Operation

To enable AAA on the router, go to configuration mode and simply enter

Router(config)#aaa new-model

Specify the protocol and location of the AAA server with one of the following lines:

tacacs-server host ip-address [single-connection]
radius-server host ip-address

The host ip-address specifies the IP address of the AAA TACACS or RADIUS server, and the single-connection option only available with TACACS specifies that the router maintain a single open connection for confirmation from an AAA/TACACS+ server (CiscoSecure Release 1.0.1 or later). The single-connection option does give better performance, but it is not the default.

The last command to get AAA up and running configures the shared password between the router and the AAA server. The passwords are case-sensitive:

tacacs-server key key
radius-server key key

A complete example looks something like this:

Router(config)#aaa new-model
Router(config)#tacacs-server host single-connection
Router(config)#tacacs-server key MyPassWord

AAA Authentication Commands

aaa authentication login specifies that you want to use authentication. You need to give the authentication parameters a list name, either default or some other name you define:

aaa authentication login {default | list-name} group 
_{group-name | radius | tacacs+} [method 2...3...4]

Using the name default means its settings are applied to all lines (console, VTY, TTY, and so on) and interfaces (async, serial, Ethernet, and so on) unless you define and use another name. A unique list name overrides the default and its settings when applied to a specific line or interface.

The group parameter has three options: a group-name, radius, or tacacs+. If you use either tacacs+ or radius, the router uses all those types of servers that you configured using the tacacs/radius-server host ip-address command, or you can build a custom group and call it with its group name. The other methods are used if the method before it has an error. One other method of special note is none with the option that if all others fail, you are authenticated. All the different authentication methods appear in Table 3.1.

Table 3.1 AAA Authentication Methods




Uses the router's enable password


Uses Kerberos Version 5

group radius

Uses the list of all RADIUS servers for authentication

group tacacs+

Uses the list of all TACACS+ servers for authentication

group group-name

Uses a subset of RADIUS or TACACS+ servers for authentication as defined by the aaa group command


Uses the line password for authentication


Uses the local username database for authentication


Uses case-sensitive local username authentication


Uses no authentication

Here is a working example of two different authentication settings:

Router(config)#aaa authentication login default group tacacs+ local
Router(config)#aaa authentication login fallback group tacacs+ enable
Router(config)#line vty 0 4
Router(config-line)#login authentication fallback

The first command builds the default list. It tries to authenticate to all TACACS servers configured, and if it receives no response, it uses the next configured setting for authentication—in this example, the local username database.

The second command creates a list called fallback. It checks the TACACS servers, and if it receives no response, it uses the enable password.

The third and fourth commands apply the fallback list to the five VTY lines, 0 through 4.


A trick question here is to ask what authentication settings are in use for Line Console 0; the answer is the default list. Remember that once a default list is built, it applies to all interfaces and lines unless overridden by an explicit assignment as you saw on the VTY ports.

Another feature worth pointing out is that when you turn on authentication using the default group, it is applied to all interfaces. You will find yourself locked out of the router if you have not finished setting up your authentication sources and you log out or your session times out.

AAA Authorization Commands

Once a user is authenticated, you can set parameters that restrict the user's access on the network using the aaa authorization command. The authorization commands have the same look and feel as the authentication command:

aaa authorization {network | exec | commands level | reverse-access} 
_{default | list-name} [method 2...3...4]

Table 3.2 lists the four areas of control where you can grant specific authorization.

Table 3.2 AAA Authorization Command




Starts authorization for all network-related service such as Serial Line Internet Protocol (SLIP) and Point-to-Point Protocol (PPP)


Starts authorization to determine whether the user is allowed to run an EXEC shell

commands level

Starts authorization for all commands at the specified privilege level (0 to 15)


For reverse access connections, such as reverse Telnet

Remember that default and list-name are simply the identifiers for the AAA parameters. You use default, or specify other non-default parameters by using list-name. There are a number of ways in which a user can be authenticated; Table 3.3 lists the options for the AAA authorization command.

Table 3.3 AAA Authorization Methods



group radius

Uses the list of all RADIUS servers for authentication.

group tacacs+

Uses the list of all TACACS+ servers for authentication.

group group-name

Uses a subset of RADIUS or TACACS+ servers for authentication as defined by the aaa group command.


Allows the user to access the requested function if the user is authenticated.


Uses the local username database for authentication.


No authorization is performed.

For authorization, let's take a look at two different examples: one for character mode and the other for packet mode. Remember, in character mode, you are usually securing the router itself:

Router(config)#aaa authorization exec default group tacacs+ none

In this example, a user must be authorized by a TACACS+ server before he can gain access to an EXEC shell or prompt. If the TACACS+ servers are unreachable, then the user is automatically granted access because of the none option at the end. This method is used mainly for administrators who still have physical access to the device.

Let's examine a packet-level example:

Router(config)#aaa authorization network checkem group tacacs+ if-authenticated
Router(config)#int serial 0
Router(config-if)#ppp authorization checkem

The first command determines whether a user is allowed to make a packet-level connection. It built a list called checkem that looks to the TACACS+ servers first; if the servers are down, it allows access if the user has been authenticated. The last command applies the checkem list to PPP services on Serial 0.

AAA Accounting Commands

Accounting allows you to track individual and group usage of network resources. When AAA accounting is activated, the router logs user activity to the TACACS+ or RADIUS server. You can then analyze this data for network management, client billing, security, or auditing. The accounting command looks like this:

aaa accounting {system | network | exec | connection | commands level} 
_{default | list-name} {start-stop | wait-start | stop-only | none} 
_ [method 2...3...4]

The aaa accounting command is unlike the authorization and authentication commands that have two halves. Accounting has three parts: what service or services you want to audit (see Table 3.4), which events trigger it, and where to send the information.

Table 3.4 AAA Accounting Command




Performs accounting for all system-level events not associated with users, such as reloads


Runs accounting for all network-related services such as SLIP and PPP


Runs accounting for an EXEC shell session


Keeps information about all outbound connections made from the router, such as Telnet and rlogin

commands level

Runs accounting for all commands at the specified privilege level (0 to 15)

Remember that default and list-name are simply the identifiers for the AAA parameters. You use default, or specify other non-default parameters by using list-name. Also worth mentioning is that the aaa accounting system command is the only command that doesn't apply to packet or character mode. The different events that you can use for accounting appear in Table 3.5.

Table 3.5 AAA Accounting Events




Sends a start accounting notice at the beginning of a process and a stop accounting notice at the end of a process. The user's process begins regardless.


Same as a start-stop except the process doesn't begin until the accounting service request is acknowledged from the AAA server.


Sends a stop accounting notice at the end of a requested user process.


Disables accounting services on this line or interface.

Then, the accounting command indicates for which server groups the information is recorded and logged. Table 3.6 lists accounting methods for server groups.

Table 3.6 AAA Accounting Methods



group radius

Uses the list of all RADIUS servers for authentication

group tacacs+

Uses the list of all TACACS+ servers for authentication

group group-name

Uses a subset of RADIUS or TACACS+ servers for authentication as defined by the aaa group command

Let's look at an example of the aaa accounting command. Here we use the command twice to set up accounting for two different events:

Router(config)#aaa accounting connection default start-stop group tacacs+
Router(config)#aaa accounting commands 15 default start-stop group tacacs+

The first command monitors any Telnet, rlogin, or other outbound connections, such as when they start and stop, and logs the information to the AAA servers configured under TACACS+.

The second command turns on accounting for privilege Level 15 commands, which is enable mode, and logs their use to the TACACS servers. You can also use Level 1 for user mode access.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020