Exploring AAA and TACAS Configuration with Cisco Modeling Labs

I’ll admit to not having executed a radical verification. Nonetheless, I’d nonetheless wager cash that AAA/RBAC companies are extra continuously talked about on Cisco certification blueprints than every other networking matter. From the CCNA to the Skilled degree, you’ll discover AAA, TACACS+, RADIUS, and RBAC listed on the examination subjects.

Here’s a handful of examples in the event you’d wish to test it out your self:

• 200-301 CCNA
  • 2.8 Describe AP and WLC administration entry connections (Telnet, SSH, HTTP, HTTPS, console, and TACACS+/RADIUS)
  • 5.8 Differentiate authentication, authorization, and accounting ideas
• 350-401 ENCOR
  • 5.1 Configure and confirm machine entry management
• 300-410 ENARSI
  • 3.1 Troubleshoot machine safety utilizing IOS AAA (TACACS+, RADIUS, native database)
• 300-430 ENWLSI
  • 8.1 Implement machine entry controls (together with RADIUS and TACACS+)
• 350-701 SCOR
  • 2.7 Configure AAA for machine and community entry comparable to TACACS+ and RADIUS
• 300-715 SISE
  • 7.0 Community Entry Gadget Administration
• 350-601 DCCOR
  • 5.xa Apply community|compute|storage safety – AAA and RBAC
• 300-615 DCIT
  • 5.xb Troubleshooting community|compute|storage safety – AAA and RBAC
• 350-501 SPCOR
  • 1.6b Describe administration aircraft safety – AAA and TACACS
• 300-540 SPCNI
  • 4.1e Implement infrastructure safety – TACACS

OMG. That’s 10 completely different certifications from Affiliate to Skilled the place these subjects present up. You’ll additionally discover them on Skilled-level exams, such because the Enterprise Infrastructure, Enterprise Wi-fi, Safety, Service Supplier, and Knowledge Heart labs. (If anybody on the market can discover one other matter with as broad a protection, please let me know within the feedback. I’d like to know what I’ve neglected up to now.)

Go to the Cisco Studying Community to view the examination subjects for all Cisco certification exams. View examination subjects

Okay… it’s undoubtedly vital… however what is AAA?

AAA is a vital matter, nevertheless it’s one which even long-time community engineers could not absolutely perceive. So earlier than we see it in motion, how a couple of fast overview of what the “triple A’s” imply?

Within the “AAA in Motion!” comedian, Carl experiences your complete AAA course of:

• The primary “A” stands for Authentication. We see this represented when Carl is prompted to confirm his id earlier than he’s allowed to make a change to the community.
• The second “A” stands for Authorization. Even after the community verifies Carl’s id, he has to examine whether or not he has the appropriate(s) to make this alteration, based mostly on which rights he has been granted on the community.
• And the third and closing “A” stands for Accounting, which Carl sees in motion when the community logs the change he makes to the community.

TACACS comes into the image to help the centralized administration of customers, roles, and logs (authentication, authorization, and accounting). Whereas every community machine could possibly be domestically configured to deal with AAA, this doesn’t scale nicely for enterprises. A greater answer is for every community machine to speak with a central “server” for these actions. TACACS is a protocol that community units and servers use to speak and deal with every of the “A’s.” A “TACACS Server” is a software program utility that helps the TACACS protocol.

Can we get to the Exploration, already?!

Now that we perceive the important function that AAA performs in a community (and that it’s a vital matter throughout many certifications), I’d like to point out you the right way to research and put together for it utilizing my favourite community simulation/virtualization software: Cisco Modeling Labs (CML). As a result of I’m all about sharing my exploration actions, I posted a few CML topology information on GitHub within the CML-community repository underneath Cisco DevNet.

You’ll see that one CML topology consists of simply an IOL router, whereas one other provides a Nexus 9000v swap to cowl knowledge middle platforms as nicely. So, after you’ve learn this weblog put up, undoubtedly obtain the topologies and discover them your self.

The best way to run a TACACS Server in Cisco Modeling Labs

Earlier than you may configure TACACS on a swap or router, you need to have a TACACS server accessible within the community. A typical TACACS server for a manufacturing community is Cisco ISE, a full “id companies engine” for machine administration, community entry, wi-fi safety, VPN entry, and extra.

Cisco ISE is a vital product and matter for community engineers. Actually, we’ve got a certification examination devoted to it. And when you can add Cisco ISE to a CML node library utilizing the node definition accessible on the CML-Neighborhood, operating a full ISE server within the topology can really feel overkill when the main target is simply on configuring TACACS for machine administration.

Fortunately, there are light-weight options. My go-to choice is the open-source “tac_plus” utility that has been accessible for a few years. Tac_plus is a fundamental Linux utility that may be downloaded and put in on most Linux distributions. Whereas lively growth of the mission appears to have stalled, it really works nice and continues to be a wonderful choice for circumstances comparable to this.

In the event you take a look at the picture of the CML topology, you’ll see “aaa-server” on the left-hand aspect of the diagram. It is a customary Ubuntu node from the CML reference platforms, with a beginning configuration setup to put in tac_plus and configure it as a fundamental TACACS server. Be at liberty to go and take a look at the configuration within the topology file for full particulars, however listed here are the fundamentals of what I did to construct my TACACS server:

1. Set up the necessities to obtain and set up the tac_plus utility from supply code.
2. Create the “tac_plus.conf” configuration file to specify the TACACS secret key, customers, and roles/privilege ranges for each IOS and NX-OS platforms.
3. Create a “tac_plus.service” file to setup tac_plus as a service.
4. Obtain, extract, set up, and begin the tac_plus server.

With the set up and configuration of the aaa-server a part of the bottom CML topology file, tac_plus will probably be operating and able to take requests as quickly because the lab is began.

cisco@aaa-server:~$ systemctl standing tac_plus
● tac_plus.service - tac_plus Service
     Loaded: loaded (/and so on/systemd/system/tac_plus.service; enabled; vendor pres>
     Energetic: lively (operating) since Mon 2024-10-14 19:16:37 UTC; 2s in the past
   Essential PID: 5982 (tac_plus)
      Duties: 1 (restrict: 2310)
     Reminiscence: 416.0K
        CPU: 2ms
     CGroup: /system.slice/tac_plus.service
             └─5982 /tacacs/sbin/tac_plus -G -C /and so on/tacacs/tac_plus.conf -d 8 >

Oct 14 19:16:37 aaa-server systemd[1]: Began tac_plus Service.
Oct 14 19:16:37 aaa-server tac_plus[5982]: Studying config
Oct 14 19:16:37 aaa-server tac_plus[5982]: Model F4.0.4.28 Initialized 1
Oct 14 19:16:37 aaa-server tac_plus[5982]: tac_plus server F4.0.4.28 beginning
Oct 14 19:16:37 aaa-server tac_plus[5982]: socket FD 4 AF 2
Oct 14 19:16:37 aaa-server tac_plus[5982]: socket FD 5 AF 10
Oct 14 19:16:37 aaa-server tac_plus[5982]: uid=0 euid=0 gid=0 egid=0 s=11063704>

The best way to allow AAA and TACACS on a Cisco IOS Router

With our TACACS server up and operational, we are able to now configure our IOS router to make use of it. Earlier than configuring the TACACS server on IOS, we have to guarantee some fundamental “pre-work” is completed on our router. IOS has been round for years and has skilled many adjustments in how authentication and authorization are dealt with.

So, the very first thing we wish to do is make sure the “new mannequin” of AAA is enabled on our machine:

aaa new-model

Subsequent, we wish to create an area consumer account that may entry and administer the machine if the TACACS server turns into unreachable. You may additionally wish to use an area account for serial/console connections.

username cisco privilege 15 secret cisco

On this command, the username and password are each set to “cisco.” (Not probably the most safe selection, however that is only a lab.) The “privilege 15” a part of the command signifies that this consumer will probably be assigned an “administrator” function. Privilege 15 is the best degree on an IOS machine and permits the consumer to execute any and all instructions.

We’re able to configure and check TACACS now. However first, I leap onto the console for the server and begin monitoring the logs. This manner, I can examine and confirm outcomes on the server aspect in addition to on the consumer.

# On aaa-server
journalctl -fu tac_plus

# Output
Oct 14 19:16:37 aaa-server systemd[1]: Began tac_plus Service.
Oct 14 19:16:37 aaa-server tac_plus[5982]: Studying config
Oct 14 19:16:37 aaa-server tac_plus[5982]: Model F4.0.4.28 Initialized 1
Oct 14 19:16:37 aaa-server tac_plus[5982]: tac_plus server F4.0.4.28 beginning
Oct 14 19:16:37 aaa-server tac_plus[5982]: socket FD 4 AF 2
Oct 14 19:16:37 aaa-server tac_plus[5982]: socket FD 5 AF 10
Oct 14 19:16:37 aaa-server tac_plus[5982]: uid=0 euid=0 gid=0 egid=0 s=1106370448

Within the above command, the “-f” argument “follows” the log messages as they arrive in.  And the “-u tac_plus” choice limits the output to solely message from the tac_plus service.

Wonderful. Now, again to the router to configure the tacacs server and add it to a gaggle of servers that the router can use for AAA service.

tacacs server aaa-server
 tackle ipv4 192.168.0.10
 key tacacs123

aaa group server tacacs+ AAA-TACACS
 server identify aaa-server

I’m all the time a fan of testing that one thing will (or seemingly will) work earlier than continuing. Conveniently, IOS helps a “check aaa” command that we are able to use.

check aaa group AAA-TACACS iosadmin admin123 legacy

# Output 
Trying authentication check to server-group AAA-TACACS utilizing tacacs+
Person was efficiently authenticated.

That appears nice! And I can see the logs on “aaa-server” as nicely.

Oct 14 19:55:16 aaa-server tac_plus[6473]: join from 192.168.0.1 [192.168.0.1]
Oct 14 19:55:17 aaa-server tac_plus[6473]: login question for 'iosadmin' port unknown-port from 192.168.0.1 accepted

With a powerful sense of confidence, let’s full the AAA configuration for all three “A’s.”

! Authentication 
aaa authentication login default group AAA-TACACS native

! Authorization 
aaa authorization exec default group AAA-TACACS native 
aaa authorization console

! Accounting
aaa accounting exec default start-stop group AAA-TACACS
aaa accounting instructions 1 default start-stop group AAA-TACACS
aaa accounting instructions 15 default start-stop group AAA-TACACS

Sustaining that sturdy sense of confidence, let’s see if it really works. Finish/exit on the router till it is advisable to log again in.

ios01 con0 is now accessible

Press RETURN to get began.

Person Entry Verification

Username: 

Attempt to log into the router utilizing the TACACS credentials for the IOS machine.

Person Entry Verification

Username: iosadmin
Password: 

ios01#

Success! Examine the logs on the server, and you must see one thing like this:

Oct 14 20:05:03 aaa-server tac_plus[6492]: login question for 'iosadmin' port tty0 from 192.168.0.1 accepted
Oct 14 20:05:03 aaa-server tac_plus[6493]: join from 192.168.0.1 [192.168.0.1]
Oct 14 20:05:03 aaa-server tac_plus[6493]: Begin authorization request
Oct 14 20:05:03 aaa-server tac_plus[6493]: do_author: consumer="iosadmin"
Oct 14 20:05:03 aaa-server tac_plus[6493]: consumer 'iosadmin' discovered
Oct 14 20:05:03 aaa-server tac_plus[6493]: exec authorization request for iosadmin
Oct 14 20:05:03 aaa-server tac_plus[6493]: exec is explicitly permitted by line 6
Oct 14 20:05:03 aaa-server tac_plus[6493]: nas:service=shell (handed through)
Oct 14 20:05:03 aaa-server tac_plus[6493]: nas:cmd* (handed through)
Oct 14 20:05:03 aaa-server tac_plus[6493]: nas:absent, server:priv-lvl=15 -> add priv-lvl=15 (ok)
Oct 14 20:05:03 aaa-server tac_plus[6493]: added 1 args
Oct 14 20:05:03 aaa-server tac_plus[6493]: out_args[0] = service=shell enter copy discarded
Oct 14 20:05:03 aaa-server tac_plus[6493]: out_args[1] = cmd* enter copy discarded
Oct 14 20:05:03 aaa-server tac_plus[6493]: out_args[2] = priv-lvl=15 compacted to out_args[0]
Oct 14 20:05:03 aaa-server tac_plus[6493]: 1 output args
Oct 14 20:05:03 aaa-server tac_plus[6493]: authorization question for 'iosadmin' tty0 from 192.168.0.1 accepted
Oct 14 20:05:03 aaa-server tac_plus[6494]: join from 192.168.0.1 [192.168.0.1]

I’ve coloured the server output to spotlight the authentication and authorization logs individually, exhibiting that they really are two completely different phases.

However what concerning the closing “A” for accounting? Press Cntr-C to cease following the service log and open up the “accounting log.”

tail -f /var/log/tac_plus.acct 

# Output 
Oct 14 20:05:03 192.168.0.1     iosadmin        tty0    async   begin   task_id=12      timezone=UTC    service=shell

It is best to see a message just like the above exhibiting the “begin” of the session on the router. Return to the router and run “write mem” to save lots of the configuration adjustments to reminiscence. A brand new log message ought to present up within the accounting log:

Oct 14 20:10:11 192.168.0.1     iosadmin        tty0    async   cease    task_id=13      timezone=UTC    service=shell   priv-lvl=15     cmd=write reminiscence 

And now, exit the router to sign off. A brand new message ought to seem as nicely:

Oct 14 20:11:02 192.168.0.1     iosadmin        tty0    async   cease    task_id=13      timezone=UTC    service=shell   disc-cause=1    disc-cause-ext=9        pre-session-time=6 elapsed_time=89  stop_time=1728936662

And BAM. All three “A’s” have been validated. Wonderful work!

Hopefully, this weblog has gotten you excited to finish your individual exploration of AAA and TACACS. And, you’re in luck—the CML topology information that I discussed above (and can once more beneath) are there so that you can seize and use immediately. Inside them are lab guides that stroll via another vital AAA subjects, comparable to utilizing native accounts on the console/serial line for IOS and configuring TACACS on Nexus units. Nonetheless, I encourage you to do some impartial exploration and experiment with issues which are not within the information:

What occurs in the event you kind the mistaken username/password? What occurs if the configured “tacacs key” is mistaken? What occurs if the TACACS server is unreachable?

Understanding the influence of issues and failures is important to a community engineer’s capacity to be snug when one thing goes mistaken in “actual life.” It’s a lot better to interrupt issues within the lab than await manufacturing to have points. And there’s no higher software than Cisco Modeling Labs for that exploration.

My very own AAA exploration will proceed. On this weblog and lab, I solely scratched the floor of the subject and data wanted for various certifications. RADIUS servers can be utilized as a substitute of TACACS, and what about AAA for issues like VPN authentication, community entry with 802.1x, or different platforms like ASA firewalls?

There are such a lot of extra prospects for me to discover in later weblog posts. Would you wish to see extra on AAA from me? Let me know within the feedback.

Till subsequent time!

Sources

 

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