This defines how many consecutive Hello intervals can pass without receiving a valid Hello from the neighbor before this device declares the Hello session on this interface timed out. This is a direct trade-off between fast fault detection and false-positive resilience to occasional lost Hello packets; a tolerance of 1 means a single missed Hello immediately tears down the adjacency, while a higher tolerance rides out brief packet loss at the cost of slower genuine-failure detection. For example, a tolerance of 3 with a 3-second Hello interval means the neighbor relationship survives up to two consecutive missed Hellos but is declared down after the third, roughly a 9-second detection window.