Path information is obtained in a VPLS-based network by generating special
Layer 2 frames (referred to herein as "trace-request frames"), performing
source MAC filtering to identify the trace-request frames, and generating
a special frame (referred to herein as a "trace-reply frame") when the
source MAC filtering identifies a trace-request frame. Upon identifying a
trace-request frame, path information is collected and embedded into the
trace-reply frame. The trace-reply frame is then sent to the originating
node where the path information is used to learn the path that the
trace-request frame traversed. By sending multiple trace-request frames
with different source MAC addresses, path information received from
source MAC filtering at different nodes in the VPLS-based network can be
collected and used to learn an entire path of interest.