Home > Articles > Certification > Cisco Certification > CCNA

TACACS+ vs. RADIUS: Similarities and Differences

If you're responsible for the security of your organization's network, it's important to examine all the possibilities. Sean Wilkins, co-author of CCNA Routing and Switching 200-120 Network Simulator, examines these two long-time AAA favorites, discussing how they protect your network's vital resources.
Like this article? We recommend

Overview

When building or operating a network (or any system) in an organization, it's important to have close control over who has access. On small networks, very few people (maybe only one person) should have the passwords to access the devices on the network; generally this information is easy to track because the number of users with access is so low. In larger organizations, however, tracking who has access to what devices at what level can quickly become complex. This is where authentication, authorization, and accounting (AAA) solutions come to the rescue. These solutions provide a mechanism to control access to a device and track people who use this access.

In modern networks, the two principal AAA solutions are the Remote Authentication Dial-In User Service (RADIUS) and Cisco's Terminal Access Controller Access-Control System Plus (TACACS+) protocols. This article discusses the services these protocols provide and compares them to each other, to help you decide which solution would be best to use on a particular network.

AAA Basics

Before we get into the specifics of RADIUS and TACACS+, let's define the different parts of AAA solutions. To make this discussion a little clearer, we'll use an access door system as an example. Let's start by examining authentication.

Authentication is the action of ensuring that the person attempting to access the door is who he or she claims to be. A simple authentication mechanism would be a fingerprint scanner; because only one person has that fingerprint, this device verifies that the subject is that specific person. (Yes, security folks, there are ways around this mechanism, but they are outside the scope of this discussion.) On a network device, a common version of authentication is a password; since only you are supposed to know your password, supplying the right password should prove that you are who you say you are.

Authorization is the next step in this process. Relying on successful authentication. authorization involves checking whether you are supposed to have access to that door. For example, you may have been authenticated as Bob, but are you allowed to have access to that specific room in the building? On a network device, are there specific commands that you should be allowed to use and others that you shouldn't? A common example in networks is the difference between a tier 1 and tier 2 engineer in a Network Operations Center (NOC): A tier 1 engineer may need to access the device and have the ability to perform a number of informative show commands, but shouldn't be able to shut down the device or change any specific configuration.

Accounting is a separate step, used to log who attempts to access the door and was or wasn't successful. A network device can log every user who authenticates a device as well as every command the user runs (or attempts to run). This step is important, as it can be used to determine potential security threats and to help find security breaches.

RADIUS Basics

RADIUS has been around for a long time (since the early 1990s) and was originally designed to perform AAA for dial-in modem users. This solution typically took effect when a user would dial into an access server; that server would verify the user and then based on that authentication would send out authorization policy information (addresses to use, duration allowed, and so on). The accounting piece of RADIUS monitored this exchange of information with each connected user. Since the authentication and authorization were so closely tied together, they were delivered with the same packet types (more on this later); whereas accounting was left as a separate process.

Modern RADIUS uses User Datagram Protocol (UDP) ports 1812 (authentication) and 1813 (accounting) for communications, while some older implementations may use ports 1645 (authentication) and 1646 (accounting). UDP is fast, but it has a number of drawbacks that must be considered when implementing it versus other alternatives. For example, when RADIUS was developed, security wasn't as important a consideration as it is today, and therefore RADIUS encrypted only the authentication information (passwords) along the traffic path.

The largest advantage of RADIUS today is that it's vendor-agnostic and supported on almost all modern platforms.

TACACS+ Basics

TACACS+ was Cisco's response to RADIUS (circa 1996), handling what Cisco determined were some shortcomings in the RADIUS assumptions and design. Overall, the purpose of both RADIUS and TACACS+ is the same—performing AAA for a system—but the two solutions deliver this protection a bit differently. TACACS+ uses the Transmission Control Protocol (TCP) rather than UDP, mainly due to the built-in reliability of TCP. Using TCP also makes TACACS+ clients aware of potential server crashes earlier, thanks to the server TCP-RST (Reset) packet.

How RADIUS and TACACS+ Address Security

The principal difference between RADIUS and TACACS+ mostly revolves around the way that TACACS+ both packages and implements AAA. TACACS+ encrypts the entire contents of the packet body, leaving only a simple TACACS+ header. This design prevents potential attackers that might be listening from determining the types of messages being exchanged between devices. TACACS+ also implements authentication, authorization, and accounting separately, which makes it possible for each functionality to be delegated to a different server, and/or even a different type of server (non-TACACS+).

TACACS+ also offers closer integration with Cisco devices, offering granular management of router commands (authorization). With a TACACS+ server, it's possible to implement command control using either access levels (which are further configured on the devices) or using command-by-command authorization based on server users and groups. RADIUS also offers this capability to some extent, but it's not as granular on Cisco devices; on some other vendors, this restriction is less limited.

TACACS+ also supports multiple protocols (other than IP), but this typically isn't a deciding factor in modern networks because the support for AppleTalk, NetBIOS, NetWare Asynchronous Service Interface (NASI), and X.25 that TACACS+ provides is irrelevant in most modern network implementations.

The biggest traditional downside to TACACS+ was that Cisco developed the protocol, and therefore it has only been widely supported on Cisco equipment. This situation is changing as time goes on, however, as certain vendors now fully support TACACS+.

Summary

Deciding which AAA solution to implement in any organization is highly dependent on both the skills of the implementers and the network equipment. Since these solutions can be used across a number of different platforms (networking and otherwise), considering them is part of your due diligence as you attempt to determine interoperability between all existing and proposed solutions.

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.

Overview


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.

Surveys

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.

Newsletters

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.

Security


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

Children


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

Marketing


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.

Choice/Opt-out


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.

Links


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