A host-only network has a network interface associated with it (vmnet1) that is marked up when the host operating system is booted. Routing server processes that operate on the host operating system automatically discover the host-only network and propagate information on how to reach the network, unless you explicitly configure them not to do so.
If you are running the routed or gated daemon only to receive routing information, the simplest solution is to run the routing configuration with the -q option so that the host-only network receives, but does not supply, routing information.
If you are running routing services to supply routing information, configure the services so that they do not advertise routes to the host-only network. The routed daemon version that is included with many Linux distributions does not support specifying that an interface should not be advertised. See the routed(8) manual page for your system for more information.
If you are using the gated daemon, you must explicitly exclude the vmnet1 interface from any protocol activity. If you need to run virtual machines on a host-only network on a multihomed system where gated is used and you experience problems, contact VMware technical support.