This is the number of backup tunnels protecting the specified interface. Because it is indexed per interface, it tells an admin how many distinct bypass tunnels stand ready to take over traffic if that specific link or the node behind it fails, letting them spot an interface with zero protecting tunnels despite an expectation of FRR coverage. For example, an admin auditing a core-facing interface expected to have redundant protection finds this reads 0, revealing that no bypass tunnel was ever actually signaled for that link even though FRR is enabled globally.