The periodic path exercising capability of the LDP tree trace feature runs in the background to test the LDP ECMP paths discovered by the tree building capability. The probe used is an LSP ping message with an IP address drawn from the sub-range of 127/8 addresses indicated by the output of the tree trace for this FEC.
The periodic LSP ping messages continuously probes an ECMP path at a user configurable rate of at least 1 message per minute. This is the minimum and default value. The increment is 1 minute. If an interface is down on a router LER, then LSP ping probes that normally go out this interface are not sent.
The LSP ping routine updates the content of the MPLS echo request message, specifically the IP address, as soon as the LDP ECMP tree trace has output the results of a new computation for the path in question.