This value specifies the neighbor router's IP address for a Multi-Chassis APS group where the working and protect circuits live on different routers; a value of 0.0.0.0, the default, means this is instead a Single-Chassis APS group with both circuits on the same router, and the configured route to the neighbor should avoid traversing the MC-APS member circuits themselves. An admin sets this to establish the signaling link used to coordinate protection switching between the two routers hosting the working and protect circuits in an MC-APS deployment. Setting tApsMcNeighborAddr to a specific address like 10.0.0.2 converts this APS group's configuration from Single-Chassis to Multi-Chassis mode, pointing at that address as the peer router.