Error if forwarded port with same host port is declared multiple times

CHANGELOG.md

@@ -4,6 +4,8 @@ IMPROVEMENTS:
 
   - Don't load plugins on any `vagrant plugin` command, so that errors
     are avoided. [GH-1418]
+  - An error will be shown if you forward a port to the same host port
+    multiple times.
 
 BUG FIXES:
 

plugins/kernel_v2/config/vm.rb

@@ -1,5 +1,6 @@
 require "pathname"
 require "securerandom"
+require "set"
 
 require "vagrant"
 require "vagrant/config/v2/util"
@@ -277,12 +278,23 @@ module VagrantPlugins
 
         # Validate networks
         has_fp_port_error = false
+        fp_host_ports     = Set.new
+
         networks.each do |type, options|
           if type == :forwarded_port
             if !has_fp_port_error && (!options[:guest] || !options[:host])
               errors << I18n.t("vagrant.config.vm.network_fp_requires_ports")
               has_fp_port_error = true
             end
+
+            if options[:host]
+              if fp_host_ports.include?(options[:host])
+                errors << I18n.t("vagrant.config.vm.network_fp_host_not_unique",
+                                :host => options[:host].to_s)
+              end
+
+              fp_host_ports.add(options[:host])
+            end
           end
         end
 

templates/locales/en.yml

@@ -456,6 +456,8 @@ en:
         nfs_requires_host: |-
           Using NFS shared folders requires a host to be specified
           using `config.vagrant.host`.
+        network_fp_host_not_unique: |-
+          Forwarded port '%{host}' (host port) is declared multiple times
         network_fp_requires_ports: |-
           Forwarded port definitions require a "host" and "guest" value
         shared_folder_hostpath_missing: |-