Exploring AAA and TACAS Configuration with Cisco Modeling Labs

I’ll admit to not having carried out a radical verification. Nonetheless, I’d nonetheless guess cash that AAA/RBAC providers are extra ceaselessly talked about on Cisco certification blueprints than another networking matter. From the CCNA to the Skilled degree, you’ll discover AAA, TACACS+, RADIUS, and RBAC listed on the examination matters.

Here’s a handful of examples when 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 reminiscent of TACACS+ and RADIUS
• 300-715 SISE
  • 7.0 Community Entry System 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 totally different certifications from Affiliate to Skilled the place these matters 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 missed to date.)

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

Okay… it’s positively necessary… however what is AAA?

AAA is a vital matter, however it’s one which even long-time community engineers might 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 the complete AAA course of:

• The primary “A” stands for Authentication. We see this represented when Carl is prompted to confirm his identification 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 identification, he has to examine whether or not he has the proper(s) to make this alteration, based mostly on which rights he has been granted on the community.
• And the third and last “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 assist 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 effectively 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 gadgets and servers use to speak and deal with every of the “A’s.” A “TACACS Server” is a software program software that helps the TACACS protocol.

Can we get to the Exploration, already?!

Now that we perceive the crucial function that AAA performs in a community (and that it’s a necessary matter throughout many certifications), I’d like to point out you learn how to examine and put together for it utilizing my favourite community simulation/virtualization device: 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 information heart platforms as effectively. So, after you’ve learn this weblog submit, positively obtain the topologies and discover them your self.

run a TACACS Server in Cisco Modeling Labs

Earlier than you’ll be able to configure TACACS on a swap or router, it’s essential to have a TACACS server out there within the community. A standard TACACS server for a manufacturing community is Cisco ISE, a full “identification providers engine” for machine administration, community entry, wi-fi safety, VPN entry, and extra.

Cisco ISE is a vital product and matter for community engineers. In reality, now we have a certification examination devoted to it. And when you can add Cisco ISE to a CML node library utilizing the node definition out there on the CML-Group, 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 alternate options. My go-to possibility is the open-source “tac_plus” software that has been out there for a few years. Tac_plus is a fundamental Linux software that may be downloaded and put in on most Linux distributions. Whereas energetic growth of the mission appears to have stalled, it really works nice and continues to be a superb possibility for circumstances reminiscent of this.

In case you take a look at the picture of the CML topology, you’ll see “aaa-server” on the left-hand facet of the diagram. It is a normal 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 below 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 software 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 many others/systemd/system/tac_plus.service; enabled; vendor pres>
     Lively: energetic (operating) since Mon 2024-10-14 19:16:37 UTC; 2s in the past
   Principal 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 many others/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>

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 modifications in how authentication and authorization are dealt with.

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

aaa new-model

Subsequent, we need to create a neighborhood person account that may entry and administer the machine if the TACACS server turns into unreachable. You may also need to use a neighborhood 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 alternative, however that is only a lab.) The “privilege 15” a part of the command signifies that this person will probably be assigned an “administrator” function. Privilege 15 is the best degree on an IOS machine and permits the person 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 facet in addition to on the shopper.

# 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” possibility 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 bunch of servers that the router can use for AAA service.

tacacs server aaa-server
 handle ipv4 192.168.0.10
 key tacacs123

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

I’m at all times a fan of testing that one thing will (or probably 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 
Making an attempt 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 effectively.

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 robust sense of confidence, let’s see if it really works. Finish/exit on the router till it’s essential log again in.

ios01 con0 is now out there

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! Verify the logs on the server, and you need to 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: person="iosadmin"
Oct 14 20:05:03 aaa-server tac_plus[6493]: person '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, displaying that they honestly are two totally different phases.

However what in regards to the last “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’s best to see a message just like the above displaying the “begin” of the session on the router. Return to the router and run “write mem” to save lots of the configuration modifications 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 log off. A brand new message ought to seem as effectively:

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 might be 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 by another necessary AAA matters, reminiscent of utilizing native accounts on the console/serial line for IOS and configuring TACACS on Nexus gadgets. Nonetheless, I encourage you to do some unbiased exploration and experiment with issues which can be not within the information:

What occurs when you sort the improper username/password? What occurs if the configured “tacacs key” is improper? What occurs if the TACACS server is unreachable?

Understanding the influence of issues and failures is crucial to a community engineer’s capacity to be snug when one thing goes improper in “actual life.” It’s a lot better to interrupt issues within the lab than look ahead to manufacturing to have points. And there’s no higher device 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 information 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 potentialities 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!

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