Can you use a self signed certificate on an external Edge Server interface?

Question

Hi,
I have a small lab deployment for evaluation purposes. The Lync FE server works great for internal users. I have now added an Edge server. For the internal interface, I have a self signed certificate from our internal CA. (no problem there) For the external
interface, I have a self signed certificate from our own external CA. I have installed the cert on the client machine of the external user and installed it for trusted operation. I have used the RUCT and digicert tools to prove that the external self signed
cert is valid (root and intermediate have been checked for validity).
At first, when logging in from the Lync 2013 client on the external users machine, I would get an error from Lync about the cert being untrusted. I have now fixed that error by adding it as trusted. At this point, there are no errors or warnings in the Event
Viewer (in the application or system logs) However, I receive the following error from the Lync client, "Were having trouble connecting to the server... blah, blah".
Here is my question. Does the Microsoft Lync 2013 client and/or the "testconnectivity.microsoft.com" tool specifically prevent or forbid the use of self signed certificates on the external interface of an Edge server? They seem too.
I can tell if the certificate is my problem or something else. Any ideas on how to trouble shoot this?
Thx

Answer 1

Drago,
Thanks for all your help. I got it working.
My problem with the Lync client error, "Were having trouble connecting to the server... blah, blah", was NOT a certificate error. It was a problem with my Lync Server Topology. (My sip default domain needed to match my user login domain.)
Let me update everyone about self-signed certificates:
YES, you can self-sign a certificate on your external edge server. It is a pain, but possible.
I have a self signed certificate from our own external CA. I have installed the cert on the client machine of the external user for trusted operation. I have used the RUCT and digicert tools to prove that the external self signed cert is valid (root and
intermediate have been checked for validity).
Here are my notes:
Create/enable your own external Certificate Authority (CA) running on a server with internet access. 
On the Lync Edge Server, run the "Lync Server 2013 - Development Wizard".
Click "Install or Update Lync Server System". (Lync will automatically determine its deployment state)
You should have already completed: Step1 and Step 2.
Run or Run Again "Step 3: Request, Install or Assign Certificates".
Install the "Edge internal" certificate.
Click "Request" button to run the "Certificate Request" wizard.
You use can "Send the request immediately to an online certificate authority" option to connect to your internal CA, and create the certificate.
Once the certificate has been created, use "Import Certificate" to import it.
Once imported, on the Edge Server, go to: (Control Panel -> Administrative Tools -> Internet Information Services (ISS) Manager -> Server Certificates -> Complete Certificate Request...
In the Lync deployment wizard - Certificate Wizard, "Assign the newly imported "edge internal" certificate.
Install the "Edge External" certificate (public Internet).
Click the "Request" button to run the "Certificate Request" wizard.
Press "next"
Select "Prepare the request now, but send it later (offline certificate request).
Supply the "Certificate Request File" name and location. (You will need the file later. It should have the file extension ".req").
Click next on the "Specify Alternate Certificate Template". (which means you are using the default options)
Give it a Friendly Name. Bit Length = 2048. I selected "Mark the certificate's private key as exportable" option.
Fill in the organization info.
Fill in the Geographical Information.
The wizard should automatically fill-in the "Subject name:" and "subject alternative name:' fields.
Select your "Configured SIP domains"
"Configure Additional Subject Alternative Names" if you want. Otherwise, next.
Verify the "certificate Request Summary". Click next.
Run the wizard script to "Complete". The wizard will create a file containing the certificate request with the file extension ".req". (Let's assume the file name is "myCert.req")
 Move your myCert.req file to your external CA. Have your CA issue the cert (based on myCert.req) and export the new cert to a file. I save it as a P7B certificate. (Let's call it "ExternalCert.p7b")
In the Lync Deployment wizard - Certificate Wizard, click on "Import Certificate" for ExternalCert.p7b.
Once imported, on the Edge Server, go to: (Control Panel -> Administrative Tools -> Internet Information Services (ISS) Manager -> Server Certificates -> Complete Certificate Request... (assign it a friendly name. Let's say "EXTERNAL-EDGE")
For the "External Edge certificate (public Internet), click "Assign".
The "Certificate Assignment" wizard will run.
Click next.
From the list, select your cert "EXTERNAL-EDGE".
Finish the wizard to "complete".
You are finished on the server.
Move the "ExternalCert.p7b" file to the machine running the lync client. Install the cert via the "Certificate Import Wizard".
When installing it to a particular Certificate Store, select the "Place all certificates in the following store" option.
Browse
Select "Trusted Root Certification Authorities"
Finish the wizard.