F5 Networks F5CAB2 Exam - Topic 1 Question 1 Discussion

The BIG-IP system uses a specific precedence algorithm to determine which virtual server (listener) should process an incoming packet when multiple virtual servers might match the criteria. Since BIG-IP version 11.3.0, the system evaluates three primary factors in a fixed order of importance:

Destination Address: The system first looks for the most specific destination match. A 'Host' address (mask /32) is preferred over a 'Network' address (mask /24, /16, etc.), which is preferred over a 'Wildcard' (0.0.0.0/0).

Source Address: If multiple virtual servers have identical destination masks, the system then evaluates the source address criteria. Again, a specific source host match is preferred over a source network or a wildcard source.

Service Port: Finally, if both destination and source specifications are equal, the system checks the port. A specific port match (e.g., 80) is preferred over a wildcard port (e.g., or 0).

Following this logic, a virtual server configured with a specific destination host, a specific source host, and a specific service port represents the highest level of specificity and thus the highest preference.