We present a probabilistic model of the stability of a virtual backbone in ad hoc networks. The model allows the computation of several metrics characterizing the dynamics of a node's random movement: (1) average time for the number of link changes of the node (i.e., instances of link creation and failure) or just failures to either drop below or exceed a given threshold, and, analogously, (2) average time for the number of active links of the node to either drop below or exceed a given threshold. The former defines the stability of the node's links and the latter is the node's degree (the number of active neighbors). Besides the stability of a virtual backbone, our model will help analyze the performance of various paradigms that rely on such link-based mobility metrics; including some backbone- or cluster-assisted routing protocols and service discovery architectures