  The Bitcoin P2P network is at the core of all communications between clients.
The reachable part of this network has been explored and analyzed by numerous
studies. Unreachable nodes, however, are, in most part, overlooked.
Nonetheless, they are a relevant part of the network and play an essential role
in the propagation of messages. In this paper, we focus on transaction
propagation and show that increasing the participation of unreachable nodes can
potentially improve the robustness and efficiency of the network. In order to
do that, we propose a few changes to the network protocol. Additionally, we
design a novel transaction propagation protocol that explicitly involves
unreachable nodes to provide better protection against deanonymization attacks.
Our solutions are simple to implement and can effectively bring immediate
benefits to the Bitcoin network.
