1. A system for cross-layer troubleshooting of application delivery, comprising: a processor configured to: collect test results from a plurality of distributed agents for a plurality of application delivery layers, wherein each of the plurality of distributed agents performs one or more active measurements for identifying an MultiProtocol Label Switching (MPLS) tunnel and identifying a type of the MPLS tunnel, wherein the type of the MPLS tunnel is selected from one of the following: an explicit MLS tunnel, an implicit MPLS tunnel, an opaque MPLS tunnel, and an invisible MPLS tunnel; and generate a graphical visualization of an application delivery state for the plurality of application delivery layers based on the test results, wherein the graphic visualization includes a link that is determined to be associated with an identified explicit MPLS tunnel, an identified implicit MPLS tunnel, an identified opaque MPLS tunnel, or an identified invisible MPLS tunnel; and a memory coupled to the processor and configured to provide the processor with instructions.