Enable DHCP server in VirtualBox

VirtualBox provides a built in default dhcp server, which will dynamically assign IP address for the guest OS (when guest OS uses NAT mode).
the default NAT engine uses 10.0.2.0 as the gateway/DNS, so Guest OS will usually get 10.0.2.15 as the IP address.

Beside that, VirtualBox also provides a way for use to manually config the dhcp server for Nat Network and Host-Only mode.
We can use below command in Windows command line to list the dhcpservers that has already been set:

$ vboxmanage list dhcpservers
NetworkName:    HostInterfaceNetworking-VirtualBox Host-Only Ethernet Adapter
IP:             192.168.56.100
NetworkMask:    255.255.255.0
lowerIPAddress: 192.168.56.101
upperIPAddress: 192.168.56.254
Enabled:        Yes

We can do this using GUI interfaces as well:

File -> Preferences -> Network

Now select the VirtualBox Host-only Ethernet adapter and edit it as shown below, then in the DHCP server tab un-check Enable server.

Now press OK twice and we should theoretically be done, but due to a bug in VBox the DHCP is not truly disabled till the time you restart the host machine (The machine on which VBox is running).

Note:
In Bridge Mode, guest OS usually get its IP addresses from the router of the Host.
If the router is configured to use predefined addresses for known mac addresses, it probably always returned the ip address which is already used by wireless adapter on host computer.