Basic :dhcp configuration works.

lib/vagrant/action/vm/network.rb

@@ -155,7 +155,14 @@ module Vagrant
           ip      = args[0]
           options = args[1] || {}
 
+          # Determine if we're dealing with a static IP or a DHCP-served IP.
+          type    = ip == :dhcp ? :dhcp : :static
+
+          # Default IP is in the 20-bit private network block for DHCP based networks
+          ip = "172.28.128.1" if type == :dhcp
+
           options = {
+            :type    => type,
             :ip      => ip,
             :netmask => "255.255.255.0",
             :adapter => nil,
@@ -167,6 +174,34 @@ module Vagrant
           # bridged interfaces
           verify_no_bridge_collision(options)
 
+          # Get the network address and IP parts which are used for many
+          # default calculations
+          netaddr  = network_address(options[:ip], options[:netmask])
+          ip_parts = netaddr.split(".").map { |i| i.to_i }
+
+          # Calculate the adapter IP, which we assume is the IP ".1" at the
+          # end usually.
+          adapter_ip    = ip_parts.dup
+          adapter_ip[3] += 1
+          options[:adapter_ip] ||= adapter_ip.join(".")
+
+          if type == :dhcp
+            # Calculate the DHCP server IP, which is the network address
+            # with the final octet + 2. So "172.28.0.0" turns into "172.28.0.2"
+            dhcp_ip    = ip_parts.dup
+            dhcp_ip[3] += 2
+            options[:dhcp_ip] ||= dhcp_ip.join(".")
+
+            # Calculate the lower and upper bound for the DHCP server
+            dhcp_lower    = ip_parts.dup
+            dhcp_lower[3] += 3
+            options[:dhcp_lower] ||= dhcp_lower.join(".")
+
+            dhcp_upper    = ip_parts.dup
+            dhcp_upper[3] = 254
+            options[:dhcp_upper] ||= dhcp_upper.join(".")
+          end
+
           # Return the hostonly network configuration
           return options
         end
@@ -191,6 +226,15 @@ module Vagrant
             @logger.debug("Created network: #{interface[:name]}")
           end
 
+          if config[:type] == :dhcp
+            # TODO: Check that there isn't another DHCP server on this network
+            # that is different.
+
+            # Configure the DHCP server for the network.
+            @logger.debug("Creating a DHCP server...")
+            @env[:vm].driver.create_dhcp_server(interface[:name], config)
+          end
+
           return {
             :adapter     => config[:adapter],
             :type        => :hostonly,
@@ -201,7 +245,7 @@ module Vagrant
 
         def hostonly_network_config(config)
           return {
-            :type    => :static,
+            :type    => config[:type],
             :ip      => config[:ip],
             :netmask => config[:netmask]
           }
@@ -210,18 +254,10 @@ module Vagrant
         # Creates a new hostonly network that matches the network requested
         # by the given host-only network configuration.
         def create_hostonly_network(config)
-          # First we need to determine a good IP for the host machine
-          # of this interface. We choose to use the network address
-          # plus 1, which is usually what is expected.
-          netaddr = network_address(config[:ip], config[:netmask])
-          parts   = netaddr.split(".").map { |i| i.to_i }
-          parts[3] += 1
-          ip      = parts.join(".")
-
           # Create the options that are going to be used to create our
           # new network.
           options = config.dup
-          options[:ip] = ip
+          options[:ip] = options[:adapter_ip]
 
           @env[:vm].driver.create_host_only_network(options)
         end

lib/vagrant/config/vm.rb

@@ -157,7 +157,9 @@ do before is certainly still possible with `VBoxManage` as well.
         # providers other than VirtualBox will not be able to satisfy
         # all types of networks.
         networks.each do |type, args|
-          if type == :hostonly
+          if type == :hostonly && args[0] == :dhcp
+            # Valid. There is no real way this can be invalid at the moment.
+          elsif type == :hostonly
             # Validate the host-only network
             ip      = args[0]
             options = args[1] || {}

lib/vagrant/driver/virtualbox.rb

@@ -72,6 +72,7 @@ module Vagrant
 
       def_delegators :@driver, :clear_forwarded_ports,
                                :clear_shared_folders,
+                               :create_dhcp_server,
                                :create_host_only_network,
                                :delete,
                                :delete_unused_host_only_networks,

lib/vagrant/driver/virtualbox_4_0.rb

@@ -9,7 +9,7 @@ module Vagrant
       def initialize(uuid)
         super()
 
-        @logger = Log4r::Logger.new("vagrant::driver::virtualbox_4_0")
+        @logger = Log4r::Logger.new("vagrant::driver::virtualbox_4_1")
         @uuid = uuid
       end
 
@@ -30,6 +30,15 @@ module Vagrant
         end
       end
 
+      def create_dhcp_server(network, options)
+        execute("dhcpserver", "add", "--ifname", network,
+                "--ip", options[:dhcp_ip],
+                "--netmask", options[:netmask],
+                "--lowerip", options[:dhcp_lower],
+                "--upperip", options[:dhcp_upper],
+                "--enable")
+      end
+
       def create_host_only_network(options)
         # Create the interface
         execute("hostonlyif", "create") =~ /^Interface '(.+?)' was successfully created$/
@@ -37,13 +46,13 @@ module Vagrant
 
         # Configure it
         execute("hostonlyif", "ipconfig", name,
-                "--ip", options[:ip],
+                "--ip", options[:adapter_ip],
                 "--netmask", options[:netmask])
 
         # Return the details
         return {
           :name => name,
-          :ip   => options[:ip],
+          :ip   => options[:adapter_ip],
           :netmask => options[:netmask]
         }
       end
@@ -69,6 +78,12 @@ module Vagrant
         end
 
         networks.each do |name|
+          # First try to remove any DHCP servers attached. We use `raw` because
+          # it is okay if this fails. It usually means that a DHCP server was
+          # never attached.
+          raw("dhcpserver", "remove", "--ifname", name)
+
+          # Delete the actual host only network interface.
           execute("hostonlyif", "remove", name)
         end
       end

lib/vagrant/driver/virtualbox_4_1.rb

@@ -30,6 +30,15 @@ module Vagrant
         end
       end
 
+      def create_dhcp_server(network, options)
+        execute("dhcpserver", "add", "--ifname", network,
+                "--ip", options[:dhcp_ip],
+                "--netmask", options[:netmask],
+                "--lowerip", options[:dhcp_lower],
+                "--upperip", options[:dhcp_upper],
+                "--enable")
+      end
+
       def create_host_only_network(options)
         # Create the interface
         execute("hostonlyif", "create") =~ /^Interface '(.+?)' was successfully created$/
@@ -37,13 +46,13 @@ module Vagrant
 
         # Configure it
         execute("hostonlyif", "ipconfig", name,
-                "--ip", options[:ip],
+                "--ip", options[:adapter_ip],
                 "--netmask", options[:netmask])
 
         # Return the details
         return {
           :name => name,
-          :ip   => options[:ip],
+          :ip   => options[:adapter_ip],
           :netmask => options[:netmask]
         }
       end
@@ -69,6 +78,12 @@ module Vagrant
         end
 
         networks.each do |name|
+          # First try to remove any DHCP servers attached. We use `raw` because
+          # it is okay if this fails. It usually means that a DHCP server was
+          # never attached.
+          raw("dhcpserver", "remove", "--ifname", name)
+
+          # Delete the actual host only network interface.
           execute("hostonlyif", "remove", name)
         end
       end

lib/vagrant/driver/virtualbox_base.rb

@@ -47,6 +47,13 @@ module Vagrant
       def clear_shared_folders
       end
 
+      # Creates a DHCP server for a host only network.
+      #
+      # @param [String] network Name of the host-only network.
+      # @param [Hash] options Options for the DHCP server.
+      def create_dhcp_server(network, options)
+      end
+
       # Creates a host only network with the given options.
       #
       # @param [Hash] options Options to create the host only network.