Check for conflicting DHCP servers

lib/vagrant/action/vm/network.rb

@@ -227,12 +227,21 @@ module Vagrant
           end
 
           if config[:type] == :dhcp
-            # TODO: Check that there isn't another DHCP server on this network
-            # that is different.
+            # Check that if there is a DHCP server attached on our interface,
+            # then it is identical. Otherwise, we can't set it.
+            if interface[:dhcp]
+              valid = interface[:dhcp][:ip] == config[:dhcp_ip] &&
+                interface[:dhcp][:lower] == config[:dhcp_lower] &&
+                interface[:dhcp][:upper] == config[:dhcp_upper]
 
-            # Configure the DHCP server for the network.
-            @logger.debug("Creating a DHCP server...")
-            @env[:vm].driver.create_dhcp_server(interface[:name], config)
+              raise Errors::NetworkDHCPAlreadyAttached if !valid
+
+              @logger.debug("DHCP server already properly configured")
+            else
+              # Configure the DHCP server for the network.
+              @logger.debug("Creating a DHCP server...")
+              @env[:vm].driver.create_dhcp_server(interface[:name], config)
+            end
           end
 
           return {

lib/vagrant/driver/virtualbox_4_0.rb

@@ -53,7 +53,8 @@ module Vagrant
         return {
           :name => name,
           :ip   => options[:adapter_ip],
-          :netmask => options[:netmask]
+          :netmask => options[:netmask],
+          :dhcp => nil
         }
       end
 
@@ -235,6 +236,26 @@ module Vagrant
       end
 
       def read_host_only_interfaces
+        dhcp = {}
+        execute("list", "dhcpservers").split("\n\n").each do |block|
+          info = {}
+
+          block.split("\n").each do |line|
+            if line =~ /^NetworkName:\s+HostInterfaceNetworking-(.+?)$/
+              info[:network] = $1.to_s
+            elsif line =~ /^IP:\s+(.+?)$/
+              info[:ip] = $1.to_s
+            elsif line =~ /^lowerIPAddress:\s+(.+?)$/
+              info[:lower] = $1.to_s
+            elsif line =~ /^upperIPAddress:\s+(.+?)$/
+              info[:upper] = $1.to_s
+            end
+          end
+
+          # Set the DHCP info
+          dhcp[info[:network]] = info
+        end
+
         execute("list", "hostonlyifs").split("\n\n").collect do |block|
           info = {}
 
@@ -248,6 +269,9 @@ module Vagrant
             end
           end
 
+          # Set the DHCP info if it exists
+          info[:dhcp] = dhcp[info[:name]] if dhcp[info[:name]]
+
           info
         end
       end

lib/vagrant/driver/virtualbox_4_1.rb

@@ -53,7 +53,8 @@ module Vagrant
         return {
           :name => name,
           :ip   => options[:adapter_ip],
-          :netmask => options[:netmask]
+          :netmask => options[:netmask],
+          :dhcp => nil
         }
       end
 
@@ -235,6 +236,26 @@ module Vagrant
       end
 
       def read_host_only_interfaces
+        dhcp = {}
+        execute("list", "dhcpservers").split("\n\n").each do |block|
+          info = {}
+
+          block.split("\n").each do |line|
+            if line =~ /^NetworkName:\s+HostInterfaceNetworking-(.+?)$/
+              info[:network] = $1.to_s
+            elsif line =~ /^IP:\s+(.+?)$/
+              info[:ip] = $1.to_s
+            elsif line =~ /^lowerIPAddress:\s+(.+?)$/
+              info[:lower] = $1.to_s
+            elsif line =~ /^upperIPAddress:\s+(.+?)$/
+              info[:upper] = $1.to_s
+            end
+          end
+
+          # Set the DHCP info
+          dhcp[info[:network]] = info
+        end
+
         execute("list", "hostonlyifs").split("\n\n").collect do |block|
           info = {}
 
@@ -248,6 +269,9 @@ module Vagrant
             end
           end
 
+          # Set the DHCP info if it exists
+          info[:dhcp] = dhcp[info[:name]] if dhcp[info[:name]]
+
           info
         end
       end

lib/vagrant/errors.rb

@@ -223,6 +223,11 @@ module Vagrant
       error_key(:no_adapters, "vagrant.actions.vm.network")
     end
 
+    class NetworkDHCPAlreadyAttached < VagrantError
+      status_code(68)
+      error_key(:dhcp_already_attached, "vagrant.actions.vm.network")
+    end
+
     class NetworkNotFound < VagrantError
       status_code(30)
       error_key(:not_found, "vagrant.actions.vm.host_only_network")

templates/locales/en.yml

@@ -422,6 +422,14 @@ en:
             overlap.
           configuring: |-
             Configuring and enabling network interfaces...
+          dhcp_already_attached: |-
+            A host only network interface you're attempting to configure via DHCP
+            already has a conflicting host only adapter with DHCP enabled. The
+            DHCP on this adapter is incompatible with the DHCP settings. Two
+            host only network interfaces are not allowed to overlap, and each
+            host only network interface can have only one DHCP server. Please
+            reconfigure your host only network or remove the virtual machine
+            using the other host only network.
           no_adapters: |-
             No available adapters on the virtual machine were found to accomodate
             for all configured networks. VirtualBox virtual machines have 8