If you are using a hardware load balancer, it will perform periodic health checks for Lync to make sure it is distributing the load evenly to all servers that are functional. Because of the checks, you may end up with a large number of protocol errors in your FE logs showing a connection error with the VIP IP from the load balancer or one of its SNAT addresses. Here is an example of the error:

Source: LS Protocol Stack
Event ID: 14502
Level: Error
A significant number of connection failures have occurred with remote server IP 10.255.106.202. There have been 120 failures in the last 180 minutes. There have been a total of 291 failures.
The specific failure types and their counts are identified below.
Instance count   - Failure Type
291                 0x80072746(WSAECONNRESET)

This can be due to credential issues, DNS, firewalls or proxies. The specific failure types above should identify the problem.

Notice in the error, the IP of my VIP is listed (10.255.106.202).

Although these are expected, if you have not specified a Hardware Load Balancing (HLB) monitoring port, they certainly cause an awful lot of unwanted noise in the logs. 

To combat the issue, enable an HLB port on your FE servers (or any other pool you are using HLB on) and configure the health checks for the load balancer to use that port instead of the port used for TLS traffic. For more information on this blog, go here.

By Kevin Peters