  This paper describes a simulation study on security attacks over Distributed
Ledger Technologies (DLTs). We specifically focus on attacks at the underlying
peer-to-peer layer of these systems, that is in charge of disseminating
messages containing data and transaction to be spread among all participants.
In particular, we consider the Sybil attack, according to which a malicious
node creates many Sybils that drop messages coming from a specific attacked
node, or even all messages from honest nodes. Our study shows that the
selection of the specific dissemination protocol, as well as the amount of
connections each peer has, have an influence on the resistance to this attack.
