This paper studies the effects of Single and Dual physical link failures to the stability of WDM networks when deployed as regular 3-degree structures. The failure impact on the source-destination pair connections is evaluated for the different topology scenarios. In this way it is possible to provide an overview of the failure effects and their relation to network metrics such as availability or cost. The results quantify how much the different network interconnection designs are affected by Single and Dual Physical link failures. The case study treats a realistic scenario, the interconnection of the NSFNET topology nodes. The main conclusions show that, when networks are designed under the same conditions, there is a linear relation between average downtime and ratio of connections affected by failures. Moreover, the most expensive optimized topologies to deploy provide higher availability.