diff --git a/doc/uncloud-manual-2020-08-01.org b/doc/uncloud-manual-2020-08-01.org
index 78dd900..6dd8fb2 100644
--- a/doc/uncloud-manual-2020-08-01.org
+++ b/doc/uncloud-manual-2020-08-01.org
@@ -236,7 +236,8 @@ VPNNetworks can be managed by all authenticated users.
 
 ** Milestones                                                       :uncloud:
 *** 1.1 (cleanup 1)
-****
+**** TODO Unify ValidationError, FieldError - define proper Exception
+     - What do we use for model errors
 *** 1.0 (initial release)
 **** TODO Initial Generic product support
      - Product
diff --git a/uncloud_net/admin.py b/uncloud_net/admin.py
index dec357a..5dad27b 100644
--- a/uncloud_net/admin.py
+++ b/uncloud_net/admin.py
@@ -1,5 +1,6 @@
 from django.contrib import admin
+from .models import ReverseDNSEntry
 
 
-# for m in [ UncloudNetwork ]:
-#     admin.site.register(m)
+for m in [ ReverseDNSEntry ]:
+    admin.site.register(m)
diff --git a/uncloud_net/models.py b/uncloud_net/models.py
index afd5004..c9c8bc3 100644
--- a/uncloud_net/models.py
+++ b/uncloud_net/models.py
@@ -4,8 +4,9 @@ import ipaddress
 from django.db import models
 from django.contrib.auth import get_user_model
 from django.core.validators import MinValueValidator, MaxValueValidator
-from django.core.exceptions import FieldError
+from django.core.exceptions import FieldError, ValidationError
 
+from uncloud_pay.models import Order
 
 class MACAdress(models.Model):
     default_prefix = 0x420000000000
@@ -194,3 +195,30 @@ class ReverseDNSEntry(models.Model):
     ip_address = models.GenericIPAddressField(null=False, unique=True)
 
     name = models.CharField(max_length=253, null=False)
+
+    def save(self, *args, **kwargs):
+        # Product.objects.filter(config__parameters__contains='reverse_dns_network')
+        # FIXME: check if order is still active / not replaced
+
+        allowed = False
+
+        for order in Order.objects.filter(config__parameters__reverse_dns_network__isnull=False,
+                             owner=self.owner):
+            network = order.config['parameters']['reverse_dns_network']
+
+            net = ipaddress.ip_network(network)
+            addr = ipaddress.ip_address(self.ip_address)
+
+            if addr in net:
+                allowed = True
+                break
+
+
+        if not allowed:
+            raise ValidationError(f"User {self.owner} does not have the right to create reverse DNS entry for {self.ip_address}")
+
+        super().save(*args, **kwargs)
+
+
+    def __str__(self):
+        return f"{self.ip_address} - {self.name}"
diff --git a/uncloud_pay/models.py b/uncloud_pay/models.py
index 00163b6..353ab94 100644
--- a/uncloud_pay/models.py
+++ b/uncloud_pay/models.py
@@ -454,6 +454,16 @@ class Product(models.Model):
 
         obj.recurring_periods.add(recurring_period, through_defaults= { 'is_default': True })
 
+        obj, created = cls.objects.get_or_create(name="reverse DNS",
+                                                 description="Reverse DNS network",
+                                                 currency=Currency.CHF,
+                                                 config={
+                                                     'parameters': [
+                                                         'network'
+                                                     ]
+                                                 })
+        obj.recurring_periods.add(recurring_period, through_defaults= { 'is_default': True })
+
 
     def __str__(self):
         return f"{self.name} - {self.description}"
@@ -968,6 +978,13 @@ class Order(models.Model):
 
         return (one_time_price, recurring_price, config)
 
+    def check_parameters(self):
+        if 'parameters' in self.product.config:
+            for parameter in self.product.config['parameters']:
+                if not parameter in self.config['parameters']:
+                    raise ValidationError(f"Required parameter '{parameter}' is missing.")
+
+
     def save(self, *args, **kwargs):
         # Calculate the price of the order when we create it
         # IMMUTABLE fields -- need to create new order to modify them
@@ -983,11 +1000,12 @@ class Order(models.Model):
             except ObjectDoesNotExist:
                 raise ValidationError(f"Recurring Period {self.recurring_period} not allowed for product {self.product}")
 
+        self.check_parameters()
+
         if self.ending_date and self.ending_date < self.starting_date:
             raise ValidationError("End date cannot be before starting date")
 
 
-
         super().save(*args, **kwargs)