1)Loadbalacer teriminates the SSL and send the plain text to CA Gateway.(when LB is not using the message why they need to decrypt it.
Terminating the SSL on LoadBalancer removes the extra CPU intensive jobs from the Gateway
2)Loadbalancer bypass the SSL ,CA gateway takes care of SSL authentication.
Terminating the SSL on the Gateway is needed for particular reasons for e.g if you are using any SOAP Service you want to download a WSDL for that particular Service then you need to Terminate ssl on the Gateway as wsdl which is fetched should have https Connection Endpoint Property in it.
If the SSL is terminated on the LB then you will get a WSDL of http Endpoint as because LB is requesting the Gateway with HTTP Protocol .
So in some scenarios you need to terminate the SSL on the gateway. You can open different ports for different service.
3)Loadbalancer terminates the SSL at their end and agiain there will SSL connection b/w LB and CA API GW.
One Major reason for SSL Termination on the LB is to get the Client IP which would be used for IP Whitelisting.
The Load Balancer can only provide the Client ip only if the SSL is terminated on the LOAD Balancer.
Please correct if i am wrong
Thanks,
Irfan