You must add host information to the /etc/hosts file for each machine in the virtual network. When typing the IP addresses used for the PPP endpoints:
Designate a PPP-specific IP address for its point-to-point link. Note that if the machine was not previously configured in a physical network, you must create an IP address for the PPP link. This address becomes the host's primary network interface.
Create a network number for the virtual network. See "Assigning a Network Number to the PPP Link" for more information.