Need suggestion for ISE distributed deployment model in two different data centers along with public certificate for HTTPS

Question

Hi Experts,
I am bit confused about ISE distributed deployment model .
I have two data centers one is DC & other one is as a DR I have  requirement of guest access service implementation using CWA and get public certificate for HTTPS to avoid certificate error on client devices :
how do i deploy ISE persona for HA in this two data centers
After reading cisco doc , understood that we can have two PAN ( Primary in DC  & Secondary in DR ) like wise for MnT (Monitoring will be as same as PAN ) however I can have 5 PSN running in secondary i.e. in DR ISE however I have confusion about HA for PSN .. since we have all PSN in secondary , it would not work for HA if it fails
Can anybody suggest me the best deployment solution for this scenario ?
Another doubt about public certificate :
 Public Certificate: The ISE domain must be a registered or part of a registered domain name on the Internet. for that I need Domain name being used from customer .
Please do correct me if I am wrong about certificate understanding :
since Guest will be the outside users , we can not use certificate from internal CA , we need to get the certificate from service provider and install the same in both the ISE servers
Can anybody explain the procedure to opt the public certificate for HTTPS from service provider ? And how do i install it in both the ISE servers ?

Answer 1

Hi there. Let me try answering your questions:
PSN HA: The PSNs are not configured as "primary" or "secondary" inside your ISE deployment. They are just PSN nodes as far as ISE is concerned. Instead, inside your NADs (In your case WLCs) you can specify which PSN is primary, which one is secondary, etc. You can accomplish this by:
1. Defining all PSN nodes as AAA radius servers inside the WLC
2. Then under the SSID > AAA Servers Tab, you can list the AAA servers in the order that you prefer. As a result, the WLC will always use the first server listed until that server fails/gets reloaded, etc. 
3. As a result, you can have one WLC or SSID prefer PSN server A (located in primary DC) while a second WLC or SSID prefer PSN server B (located in backup DC)
Last but not the least, you could also place PSNs behind a load balancer and that way the traffic would be equally distributed between multiple PSNs. However, the PSN nodes must be Layer 2 adjacent, which is probably not the case if they are located in two different Data Centers
Certificates: Yes, you would want to get a public certificate to service the guest portal. Getting a public/well known certificate would ensure that most devices out there would trust the CA that signed your ISE certificate. For instance, VeriSign, GoDaddy, Entrust are some of the ones out there that would work just fine. On the other hand, if you use a certificate that was signed by your internal CA, then things would be fine for your internal endpoints that trust your internal CA but for any outsiders (Guests, contractors, etc) that do not trust and do not know who your internal CA is would get a certificate error when being redirected to the ISE guest portal. This in general is only a "cosmetic" issue and if the users click "continue" and add your CA as a trusted authority, the guest page would load and the session would work. However, most users out there would not feel safe to proceed and you will most likely get a lot of calls to your helpdesk :)
I hope this helps!
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