On this Internet if you don't trust third parties to route all of your traffic through and peers are behind NAT or CGNATs. Or imagine a mixed network with some peers on https://en.wikipedia.org/wiki/Wireless_ad_hoc_network (s), possibly with some connected to the Internet. The key assumption we have (for the random walk to work) is that it must be a small-world network (https://en.wikipedia.org/wiki/Small-world_network) and network topologies surprisingly often are.