Cisco Identity Services Engine – Part 1 – Overview

What is the Cisco Identity Services Engine?

Today’s enterprise network is rapidly changing, especially when it comes to employee mobility. Employees are no longer tethered to desktop workstations, but instead access enterprise resources via a variety of devices: tablets, smartphones, and personal laptops, just to name a few. Being able to access resources from anywhere greatly increases productivity, but it also increases the probability of data breaches and security threats because you may not control the security posture of devices accessing the network. Keeping track of all devices accessing the network is a huge task in itself, and as the need for more access arises, the more unsustainable it becomes to manage.

The Cisco Identity Services Engine (ISE) is an identity-based network access control and policy enforcement system. ISE allows a network administrator to centrally control access policies for wired and wireless endpoints based on information gathered via RADIUS messages passed between the device and the ISE node, also known as profiling. The profiling database is updated on a regular basis to keep up with the latest and greatest devices so there are no gaps in device visibility.

Essentially, ISE attaches an identity to a device based on user, function, or other attributes to provide policy enforcement and security compliance before the device is authorized to access the network. Based on the results from a variety of variables, an endpoint can be allowed onto the network with a specific set of access rules applied to the interface it is connected to, else it can be completely denied or given guest access based on your specific company guidelines.

Let’s analogize LOTR-style for clarification: ISE is Gandalf, and the end-user device is the pursuing Balrog. I think you know where this is going.


ISE an automated policy enforcement engine that takes care of the mundane day-to-day tasks like BYOD device onboarding, guest onboarding, switchport VLAN changes for end-users, access list management, and many others, so a network administrator can focus on other important tasks (and cool projects!).

ISE Basics

The ISE platform is typically a distributed deployment of nodes made up of three different personas: Policy Administration Node (PAN), Monitoring and Troubleshooting Node (MnT), and Policy Services Node (PSN). All three roles are required for ISE to function.

Policy Administration Node (PAN)

The PAN persona is the interface an administrator logs into in order to configure policies. It is the control center of the deployment. This node allows an administrator to make changes to the entire ISE topology, and those changes are pushed out from the admin node to the Policy Services Nodes (PSN).

Policy Services Node (PSN)

The PSN persona is where policy decisions are made. These are the nodes where network enforcement devices send all network messaging to; RADIUS messaging is an example of what is sent to the PSNs. The messages are processed and the PSN gives the go/no-go for access to the network.

Monitoring and Troubleshooting Node (MnT)

The MnT persona is where logging occurs and reports are generated. All logs are sent to this node and it sorts through them so it can assemble them in a legible format. It is also used to generate various reports so you can make management happy with pretty pictures and numbers (*wink wink*) as well as notify you of any alarms for ISE.

How ISE Works

Now that you know what each persona does, let’s take a look at how everything fits together as a complete system. The diagram shows a logical representation of ISE, because the personas may be distributed across many different appliances. Familiarize yourself with the figure below, and I will explain what each piece is doing:
ISE Communication Model

The figure above is from the Cisco Trustsec How-To Guide: ISE Deployment Types and Guidelines. If you’re considering deploying ISE, I really recommend reading all ISE Design Guides before you plan your implementation.

  1. Communication starts with the endpoint. This could be a laptop, smartphone, tablet, security camera, videoconferencing system — anything that requires network access.
  2. The client must connect through a network access device — a switch, a wireless LAN controller, or a VPN concentrator — in order to gain access to the network. This is where enforcement of all policies takes place.
  3. The endpoint is asked for authentication via an 802.1X request, and that request is sent to the Policy Services Node.
  4. At this point, the PSN has already been given a specific configuration from the Admin node. The PSN will process the credentials (it may need to query an external database for this; LDAP or Active Directory, for example), and based on the configuration set the PSN will make an authorization decision.
  5. The PSN sends the decision back to the network access device so it can enforce the decision. The network access device is sent specific actions to take for the session. Many actions can be taken at this point depending on the policy, but a few common features are dynamic access lists, change of authorization (to switch VLANs, for example), and Security Group Tags (part of the Cisco TrustSec solution).
  6. Now the client can access specific resources based on what the PSN has sent back as a rule set. Alternatively, the client can be redirected to the guest login page or completely denied access to the network.
  7. All of these messages passed back and forth are all logged to the monitoring node, where they can be viewed from the admin node in an organized format.

This is definitely a complex beast with a lot of moving parts, but as long as you keep the fundamentals in mind and break it down into different parts, it’s not too tough to implement and troubleshoot. The most time-consuming part of a deployment is figuring out your policies for authorization. Once you have standard policies across the board, enforcing those policies is a breeze with ISE. I will go into policies in my next post, but let’s move onto the last topic for the overview: Deployment Topologies and Licensing.

Physical Deployment Examples

What I’m about to say here is probably the most important part of a deployment: DO NOT TRY TO SAVE MONEY BY GIVING UP HIGH AVAILABILITY! These nodes control access to your entire network. If these nodes go down, you might as well have a total network failure because nobody will get authenticated or authorized. Design ISE with as much high availability as you can afford. The only time a standalone deployment is acceptable is if you are doing a very small proof-of-concept which does not effect production end-users.

The other important part of a deployment is the hardware chosen to implement ISE on. Now, Cisco does offer an ESX/ESXi option, however, I don’t recommend that for a few reasons. First and foremost, the appliance option is tested and rated to scale to a certain number of endpoints. If you use the ESX/ESXi option, you are losing a little bit of that predictability. I said it before and I will say it again, these nodes control access to your entire network, so if you have unpredictable performance, then you will have unpredictable issues. The other thing I don’t like about an ESX/ESXi option is troubleshooting. If you do have an issue with ISE, you really want it resolved quickly. If you’re using the VM deployment and something goes wrong, you have to open tickets with Cisco, your server manufacturer, VMWare, and anything else that may be tied to your deployment. That’s not incredibly efficient, and you’re likely to run into a lot of vendor finger-pointing before you finally get the issue resolved. If you go with the Cisco appliance route, you open a ticket with Cisco, and that’s it! Smartnet covers the software and the hardware, so it makes the issue resolution process much simpler. I will say it one last time: These nodes control access to your entire network!

With that said, let’s get into the actual deployment options:

  • Standalone
    • One node running all three personas (PAN, MnT, PSN).
    • No redundancy.
    • Limited to a maximum of 2000 endpoints, regardless of hardware type.
  • Two-Node Deployment
    • Two nodes running all three personas (PAN, MnT, PSN).
    • Simple redundancy – one node is assigned the primary admin role and secondary monitoring role, and the other node is assigned the secondary admin role and primary monitoring role. They both run the policy services node, and network access devices are configured to use both PSNs.
    • Still limited to a maximum of 2000 endpoints.
  • Mid-sized Deployment – Separate Policy Services Nodes
    • Two nodes taking on the admin and monitoring persona, but no policy service persona.
    • Policy service nodes are standalone boxes. You can have up to 5 PSNs in a deployment where the PAN and MnT are collocated.
    • Limited to a maximum of 10000 endpoints regardless of hardware capacity.
  • Large Deployment
    • Every persona has its own dedicated node. You have a primary admin node, a secondary admin node, a primary monitoring node, a secondary monitoring node, and up to 40 policy services nodes. This deployment is so large that you will likely need load balancers to serve virtual IPs with a group of PSNs sitting behind it.
    • The endpoint capacity is based on the hardware of nodes. Prior to ISE version 1.2, the maximum capacity was 100000 endpoints. In version 1.2, that limitation was increased to 250000 endpoints.

If you’re looking for the performance metrics for each appliance, take a look at the design guides I linked to above. There are plenty of charts and other goodies to explain everything.

Got it? Good! Onto licensing this bad boy!


ISE is offered in a few different flavors of licensing: functionality-based or deployment-based.

Functionality-based is the “full-steam ahead” type of licensing where all network access devices are supported and feature-sets are licensed. You can choose from the Base License or Base + Advanced License. The Base License is for deployments that only need to authenticate and authorize users and devices, provision guest users, access reporting features, and monitor and troubleshoot access to the network. The base license is perpetual (it has no term subscription limit). The Advanced License expands on the base license and enables organizations to make more advanced decisions (it has all of the cool features that you really want in a deployment). The features include device onboarding and provisioning, device profiling and feed service, posture services, mobile device management integration, and security group access capabilities. This license is term-based with a choice of 3- or 5-year term subscriptions. The base license is a prerequisite for the advanced license.

Deployment-based licensing is the slow, phased approach to deploying ISE. This type of licensing allows you to start with wireless endpoints only and expand to wired and VPN later when your organization is ready. Due to the complexity of ISE, I recommend using the phased approach and really getting to know the product before rolling it out to the entirety of the network. The Wireless License includes everything that the base + advanced license does, but it only applies to wireless network access devices. The wireless license is term-based with a choice of 3- or 5-year term subscriptions. This license typically satisfies most BYOD (Bring Your Own Device) policies management may be asking for. Once ISE has been proven effective on the wireless front, it’s typically pretty easy to justify rolling it out to wired and VPN devices as well using the Wireless Upgrade License. The wireless upgrade license is the same as wireless, but it expands the functionality of ISE to wired and VPN network access devices. It is also licensed on 3- or 5-year terms.

Along with the term length, each license has an endpoint limit (100, 250, 500, 1000, 1500, and so on). Keep in mind, this is not total endpoints, but simultaneously authorized endpoints. If an endpoint isn’t authorized, it doesn’t increment the license count. If an endpoint is authorized and then leaves the network, the license count decrements because it is de-authorized.

SO! Hopefully this information was helpful. It’s a lot to take in, and there are many nooks and crannies to navigate in order to have a successful ISE deployment. Keep an eye out for Part 2: Wireless ISE Deployment, where I’ll get into the technical details of the deployment type most organizations decide to start with.

As always, leave a comment below or send me an email at with any questions!

16 thoughts on “Cisco Identity Services Engine – Part 1 – Overview

    1. Thank you! I promise it’s coming soon. I’ll be blocking out some time in June to dedicate to building this lab, so expect some more ISE content around mid-to-late June.

  1. what if the MNT and PAN nodes are down for “Mid-sized Deployment – Separate Policy Services Nodes”? The PSN still can function?

    1. That’s correct! The PSNs get their configuration from the PAN node and only gets an updated configuration if it changes. If the PAN and MNT nodes are down, then the PSNs still function with the configuration that has been replicated from the PAN.

      However, you wouldn’t be able to see any logs or make any configuration changes without the PAN up and running. Chances are, both the primary and secondary PAN/MNT nodes won’t be down at the same time. If both the primary and secondary nodes for each role is down, you probably have a bigger problem and ISE is going to be the least of your worries.

  2. I was trying to get some stuff about ISE. It is very informative for me !!!!!!!!!
    Thank you Very much
    i am planning this for my campus network we got a Base+Advanced license is this enough for my wireless and wired clients (with BYOD)

    1. You are very welcome! I need to update my post because Cisco has changed their licensing a bit. Base+Advanced should likely be fine for you. Are you looking to do posture assessment for your hosts as well?

  3. Hello Garret,

    This guide is great.
    I have a little question :
    In large deployment, are there latency requirements between High availability ISE infrastructure?
    For example an ISE in a DC in Paris and another one in a DC in New-York ?
    I’ve read somewhere that the latency should be less than 200ms… But I do not find where I read this :(


    1. Hi Natale,

      As a general rule, deployments should not cross major geographical locations.

      The databases are constantly synchronizing, and all pending updates MUST be completed within one second of the change. Essentially that means:

      1/[(endpoint updates/sec)]

      So, if you have an average of 20 updates per second, you’re limited to a 50ms round-trip latency time. So, as you scale out to a larger deployment, the amount of endpoint updates/second also goes up, which makes that latency even more critical, and the round-trip time has to go down.

      As an example, when we’re talking about US and APAC being ~200 ms apart, you’re limited to 5 endpoint updates per second, which is not very much. Memory and performance would be severely impacted if those updates started to queue up.

      1. lovely answer,, i was looking for that too … and great info to share about ISE and looking foreword for Part 2

  4. Great article, Garret! Thanks a lot. Not to nitpick but you’ve got typo in the following sentence…

    “The wireless upgrade license is the same as wireless”


  5. Esta magnifico este tutorial, le agradeceria enormemente que en algun futuro no muy lejano, nos comparta la parte 2.


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