We now discuss a few important aspects about Listen and Whisper not covered earlier.
Hijacking unallocated prefixes: With the deployment of Whisper, a malicious adversary can still claim ownership over unallocated address spaces without triggering alarms by propagating bogus announcements. One way of dealing with this problem is to request ICANN [3] to specifically advertise unallocated address spaces with its own corresponding Whisper signatures whenever it notices an advertisement for an unallocated prefix. Additionally, to avoid a DoS attack on ICANN for such prefixes, routers should not maintain forwarding entries for these prefixes.
Route Aggregation: Whenever an AS aggregates several route advertisements into one, it is required to perform one of the following operations to maintain the consistency of the aggregated route: (a) Append the individual signatures corresponding to each advertisement so that an upstream AS can match at least one of the signatures with the whisper signatures for alternate routes to sub-prefixes. (b) If the AS owns the entire aggregated prefix (common form of aggregation in BGP), ignore the whisper signatures in the sub-prefixes and append its own whisper signature.
Other types of security attacks: Other than propagation of invalid routes, one can imagine other forms of routing attacks or misconfiguration errors which may result in routing loops, persistent route oscillations or convergence problems. Such problems are out of the scope of this paper.