F5 LTM (ADC) question

AhmedMS In your screenshots I only see that you are comparing service port (SP) in the pool at the Virtual Server (VS) which has no distinction other than one is in the pool and the other is in the VS. The SP is the port in which you want that configuration to listen on, so in the VS this is the port the VS will listen on and receive traffic with the specific perameters of source address, destination address, service port, and protocol. Typically you match the SP in the VS to the same SP for the pool members (PM) in the pool but you can mismatch then as you mentioned above. One of the reasons you might mismatch would be a common one where the VS listens on 443 and decrypts SSL for HTTPS traffic and then passes that decrypted traffic to the pool member on 81 so that those individuals who manage the website can differentiate between HTTP traffic on 80 and HTTPS traffic received on port 81. Again ultimately the ports not matching is completely up to the individuals who use that particular virtual server and who manage the servers that you are balancing to.

This second piece, the alias port in the health monitor is a way to force the health monitor to check a different port than what the PM is listening on with its configured SP. By default if your PM is configured to listen on port 80 then the health check without an alias port will send the health check to port 80 as well. So the PM could be listening on 81 but you want to health check on 8080 to validate something else that the server is doing that could be a dependancy for the website working that port 81 couldn't validate properly. Hopefully this is what you were looking for but if you require additional information please let us know and we can hopefully assist with that.

Hi AhmedMS , 
Virtual server port : is the port that you assign to the virtual server to listen on , for EX: you need to publish a { http } Application , so you shoud create a virtual server ip with the proper service port { 80 for http } to map all connections which destinated to your http application via this virtual server. 
NOTE : you do not have to assign port 80 for http traffic you can use any custom port , I use it for simplicity. 

The Alias service port in Monitors : from its name it is a monitoring related , you want to create a custom monitor to check the availability if this application runs this port properly or not. 
For Example : you have a application server listens on port 777 and you need to check if this service port up and available or not in this case , you do not only assign a normal tcp monitor which perform only {SYN , SYN-ACK , ACK} you need to be more specific and check the service itself up and running or not , so when you create an Alias with service port "777" it will go to check the service itself periodically it will ask for "777" I want to say that.

this is widely used when you want to monitor the Backend servers which listen on differnet ports other than the pool members service ports. 

I hope you find this answer insightful.

Dear Mohamed, Mike, Paulius 

Many thanks for your support, your time, and your efforts. You all made my point, and I appreciate that very much. 

Kind Regards,