Hold-down is another distance-vector loop-avoidance technique, whereby hosts ignore updates for a period of time until link failure news has had a chance to propagate. Consider the networks in Figure 4.51, where all links have cost 1, except E-D with cost 10. Suppose that the E-A link breaks and B reports its loopforming E route to A immediately afterward (this is the false route, via

A). Specify the details of a hold-down interpretation, and use this to describe the evolution of the routing loop in both networks.

To what extent can hold down prevent the loop in the EAB network without delaying the discovery of the alternative route in the EABD network?

Figure 4.51