diff -ur admin.o/handlers/dns/forward_zone.py admin/handlers/dns/forward_zone.py
--- admin.o/handlers/dns/forward_zone.py	2011-10-13 10:12:44.000000000 +0200
+++ admin/handlers/dns/forward_zone.py	2011-10-13 10:13:31.000000000 +0200
@@ -54,7 +54,7 @@
 	'zone': univention.admin.property(
 			short_description=_('Zone name'),
 			long_description='',
-			syntax=univention.admin.syntax.string,
+			syntax=univention.admin.syntax.dnsZone,
 			multivalue=0,
 			options=[],
 			required=1,
diff -ur admin.o/syntax.py admin/syntax.py
--- admin.o/syntax.py	2011-10-13 10:12:44.000000000 +0200
+++ admin/syntax.py	2011-10-13 10:15:47.000000000 +0200
@@ -937,6 +937,21 @@
 			return text
 		raise univention.admin.uexceptions.valueError,_("The name of a reverse zone consists of the reversed subnet address followed by .in-addr.arpa. Example: \"0.168.192.in-addr.arpa\"")
 
+class dnsZone(simple):
+	name='dnsZone'
+        _re = re.compile(r'^[a-zA-Z](:?(:?[a-zA-Z0-9-]{0,63})*\.?)*[a-zA-Z0-9]$')
+
+        def parse(self, text):
+                if text is None:
+                        raise univention.admin.uexceptions.valueError(_("Missing value!"))
+                if len(text) >= 255:
+                        raise univention.admin.uexceptions.valueError(_("Value may not be longer than 255 chars!"))
+                if self._re.match(text) is not None:
+                        return text
+                elif max(map(len, text.split('.'))) >= 63:
+                        raise univention.admin.uexceptions.valueError(_("Value may not longer than 63 chars between dots!"))
+                raise univention.admin.uexceptions.valueError(_("Value may not contain other than numbers, letters and dots and may not end with a dot!"))
+
 class dnsName(simple):
 	name='dnsName'
 	_re = re.compile('^[a-zA-Z0-9][a-zA-Z0-9._-]*[a-zA-Z0-9.]$')