"Bidirectional Forwarding Detection (BFD) requires that messages be transmitted at regular intervals and provides a way to negotiate the interval used by BFD peers. Some BFD implementations may be restricted to only support several interval values. When such BFD implementations speak to each other@ there is a possibility of two sides not being able to find a common value for the interval to run BFD sessions. This document updates RFC 5880 by defining a small set of interval values for BFD that we call ""Common Intervals"" and recommends implementations to support the defined intervals. This solves the problem of finding an interval value that both BFD speakers can support while allowing a simplified implementation as seen for hardware-based BFD. It does not restrict an implementation from supporting more intervals in addition to the Common Intervals."