diff --git a/README.md b/README.md
index 5da7256..8a717d2 100644
--- a/README.md
+++ b/README.md
@@ -6,11 +6,11 @@ A small, lightweight and extensible DynDNS server written with Ruby and Rack.
 
 ## Description
 
-dyndnsd.rb is aimed to implement a small [DynDNS-compliant](http://dyn.com/support/developers/api/) server in Ruby. It has an integrated user and hostname database in it's configuration file that is used for authentication and authorization. Besides talking the DynDNS protocol it is able to invoke an so-called *updater*, a small Ruby module that takes care of supplying the current host => ip mapping to a DNS server.
+dyndnsd.rb aims to implement a small [DynDNS-compliant](http://dyn.com/support/developers/api/) server in Ruby supporting IPv4 and IPv6 addresses. It has an integrated user and hostname database in it's configuration file that is used for authentication and authorization. Besides talking the DynDNS protocol it is able to invoke an so-called *updater*, a small Ruby module that takes care of supplying the current host => ip mapping to a DNS server.
 
-The is currently one updater shipped with dyndnsd.rb `command_with_bind_zone` that writes out a zone file in BIND syntax onto the current system and invokes a user-supplied command afterwards that is assumed to trigger the DNS server (not necessarily BIND since it's zone files are read by other DNS servers too) to reload it's zone configuration.
+There is currently one updater shipped with dyndnsd.rb `command_with_bind_zone` that writes out a zone file in BIND syntax onto the current system and invokes a user-supplied command afterwards that is assumed to trigger the DNS server (not necessarily BIND since it's zone files are read by other DNS servers too) to reload it's zone configuration.
 
-Because of the mechanisms used dyndnsd.rb is known to work only on *nix systems.
+Because of the mechanisms used dyndnsd.rb is known to work only on \*nix systems.
 
 ## General Usage
 
@@ -112,6 +112,14 @@ where:
 * HOSTNAMES is a required list of comma separated FQDNs (they all have to end with your config.yaml domain) the user wants to update
 * MYIP is optional and the HTTP client's address will be used if missing
 
+### IP address determination
+
+The following rules apply:
+
+* use any IP address provided via the myip parameter when present, or
+* use any IP address provided via the X-Real-IP header e.g. when used behind HTTP reverse proxy such as nginx, or
+* use any IP address used by the connecting HTTP client
+
 ### SSL, multiple listen ports
 
 Use a webserver as a proxy to handle SSL and/or multiple listen addresses and ports. DynDNS.com provides HTTP on port 80 and 8245 and HTTPS on port 443.
diff --git a/lib/dyndnsd.rb b/lib/dyndnsd.rb
index 163d4ce..c836aea 100644
--- a/lib/dyndnsd.rb
+++ b/lib/dyndnsd.rb
@@ -44,11 +44,11 @@ module Dyndnsd
       @db['hosts'] ||= {}
       (@db.save; update) if @db.changed?
     end
-    
+
     def update
       @updater.update(@db)
     end
-    
+
     def is_fqdn_valid?(hostname)
       return false if hostname.length < @domain.length + 2
       return false if not hostname.end_with?(@domain)
@@ -56,45 +56,52 @@ module Dyndnsd
       return false if not name.match(/^[a-zA-Z0-9_-]+\.$/)
       true
     end
-    
+
     def call(env)
       return @responder.response_for_error(:method_forbidden) if env["REQUEST_METHOD"] != "GET"
       return @responder.response_for_error(:not_found) if env["PATH_INFO"] != "/nic/update"
-      
+
       params = Rack::Utils.parse_query(env["QUERY_STRING"])
-      
+
       return @responder.response_for_error(:hostname_missing) if not params["hostname"]
-      
+
       hostnames = params["hostname"].split(',')
-      
+
       # Check if hostname match rules
       hostnames.each do |hostname|
         return @responder.response_for_error(:hostname_malformed) if not is_fqdn_valid?(hostname)
       end
-      
+
       user = env["REMOTE_USER"]
-      
+
       hostnames.each do |hostname|
         return @responder.response_for_error(:host_forbidden) if not @users[user]['hosts'].include? hostname
       end
 
-      # no myip?
-      if not params["myip"]
-        params["myip"] = env["REMOTE_ADDR"]
+      # fallback value, always present
+      myip = env["REMOTE_ADDR"]
+
+      # check whether X-Real-IP header has valid IPAddr
+      if env.has_key?("HTTP_X_REAL_IP")
+        begin
+          IPAddr.new(env["HTTP_X_REAL_IP"])
+          myip = env["HTTP_X_REAL_IP"]
+        rescue ArgumentError
+        end
       end
-      
-      # malformed myip?
-      begin
-        IPAddr.new(params["myip"])
-      rescue ArgumentError
-        params["myip"] = env["REMOTE_ADDR"]
+
+      # check whether myip parameter has valid IPAddr
+      if params.has_key?("myip")
+        begin
+          IPAddr.new(params["myip"])
+          myip = params["myip"]
+        rescue ArgumentError
+        end
       end
-      
-      myip = params["myip"]
-      
+
       Metriks.meter('requests.valid').mark
       Dyndnsd.logger.info "Request to update #{hostnames} to #{myip} for user #{user}"
-      
+
       changes = []
       hostnames.each do |hostname|
         if (not @db['hosts'].include? hostname) or (@db['hosts'][hostname] != myip)
@@ -106,7 +113,7 @@ module Dyndnsd
           Metriks.meter('requests.nochg').mark
         end
       end
-      
+
       if @db.changed?
         @db['serial'] += 1
         Dyndnsd.logger.info "Committing update ##{@db['serial']}"
@@ -114,7 +121,7 @@ module Dyndnsd
         update
         Metriks.meter('updates.committed').mark
       end
-      
+
       @responder.response_for_changes(changes, myip)
     end
 
@@ -130,23 +137,23 @@ module Dyndnsd
         puts "Config file not found!"
         exit 1
       end
-      
+
       puts "DynDNSd version #{Dyndnsd::VERSION}"
       puts "Using config file #{config_file}"
 
       config = YAML::load(File.open(config_file, 'r') { |f| f.read })
-      
+
       if config['logfile']
         Dyndnsd.logger = Logger.new(config['logfile'])
       else
         Dyndnsd.logger = Logger.new(STDOUT)
       end
-      
+
       Dyndnsd.logger.progname = "dyndnsd"
       Dyndnsd.logger.formatter = LogFormatter.new
 
       Dyndnsd.logger.info "Starting..."
-      
+
       # drop privs (first change group than user)
       Process::Sys.setgid(Etc.getgrnam(config['group']).gid) if config['group']
       Process::Sys.setuid(Etc.getpwnam(config['user']).uid) if config['user']
@@ -174,7 +181,7 @@ module Dyndnsd
       db = Database.new(config['db'])
       updater = Updater::CommandWithBindZone.new(config['domain'], config['updater']['params']) if config['updater']['name'] == 'command_with_bind_zone'
       responder = Responder::DynDNSStyle.new
-      
+
       # configure rack
       app = Daemon.new(config, db, updater, responder)
       app = Rack::Auth::Basic.new(app, "DynDNS") do |user,pass|
diff --git a/spec/daemon_spec.rb b/spec/daemon_spec.rb
index 1b9385e..06fc743 100644
--- a/spec/daemon_spec.rb
+++ b/spec/daemon_spec.rb
@@ -166,4 +166,11 @@ describe Dyndnsd::Daemon do
     last_response.should be_ok
     last_response.body.should == 'good 127.0.0.1'
   end
+
+  it 'uses clients remote IP address from X-Real-IP header if behind proxy' do
+    authorize 'test', 'secret'
+    get '/nic/update?hostname=foo.example.org', '', 'HTTP_X_REAL_IP' => '10.0.0.1'
+    last_response.should be_ok
+    last_response.body.should == 'good 10.0.0.1'
+  end
 end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index e766e4f..1d6a8ce 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -6,3 +6,7 @@ require 'rack/test'
 require 'dyndnsd'
 require 'support/dummy_database'
 require 'support/dummy_updater'
+
+RSpec.configure do |config|
+  config.expect_with(:rspec) { |c| c.syntax = :should }
+end