Assuming you are running Mongo in a VM for testing, it's handy for MongoDB to listen on all interfaces. This allows the host or other VMs to access the database. Assuming you are using a bridged network interface, you can just change bindIp: to bindIpAll: true in /etc/mongod.conf.

If you are using NAT, it will also be necessary to map a port on the host to port 27017 in the guest. To expose it for a single host, you can map a port on localhost to the guest. For instance:

Name Protoco Host IP Host Port Guest IP Guest Port
Mongo TCP 127.0.01 27017 27017

localhost:27017 is the default database address used by the mongo client, so no changes are needed. If you do change the port, the host and port must be supplied on the command line.

This article on Stack Overflow has more information: