diff --git a/src/main/java/net/hostsharing/hsadminng/hs/hosting/asset/HsHostingAssetType.java b/src/main/java/net/hostsharing/hsadminng/hs/hosting/asset/HsHostingAssetType.java
index 32388aa0..6a0846a9 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/hosting/asset/HsHostingAssetType.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/hosting/asset/HsHostingAssetType.java
@@ -21,6 +21,9 @@ import static java.util.stream.Collectors.toSet;
 import static net.hostsharing.hsadminng.hs.hosting.asset.EntityTypeRelation.*;
 import static net.hostsharing.hsadminng.hs.hosting.asset.HsHostingAssetType.RelationPolicy.OPTIONAL;
 import static net.hostsharing.hsadminng.hs.hosting.asset.HsHostingAssetType.RelationPolicy.REQUIRED;
+import static net.hostsharing.hsadminng.hs.hosting.asset.HsHostingAssetType.RelationType.ASSIGNED_TO_ASSET;
+import static net.hostsharing.hsadminng.hs.hosting.asset.HsHostingAssetType.RelationType.BOOKING_ITEM;
+import static net.hostsharing.hsadminng.hs.hosting.asset.HsHostingAssetType.RelationType.PARENT_ASSET;
 
 public enum HsHostingAssetType implements Node {
     SAME_TYPE, // pseudo-type for recursive references
@@ -135,43 +138,49 @@ public enum HsHostingAssetType implements Node {
     // TODO.refa: try to get rid of the following similar methods:
 
     public RelationPolicy bookingItemPolicy() {
-        return stream(relations).filter(r -> r.relatedType instanceof HsBookingItemType)
-                .map(r -> r.relationType)
+        return stream(relations)
+                .filter(r -> r.relationType == BOOKING_ITEM)
+                .map(r -> r.relationPolicy)
                 .reduce(HsHostingAssetType::onlyASingleElementExpectedException)
                 .orElse(RelationPolicy.FORBIDDEN);
     }
 
     public HsBookingItemType bookingItemType() {
-        return stream(relations).filter(r -> r.relatedType instanceof HsBookingItemType)
-                .map(r -> HsBookingItemType.valueOf(r.relatedType.toString()))
+        return stream(relations)
+                .filter(r -> r.relationType == BOOKING_ITEM)
+                .map(r -> HsBookingItemType.valueOf(r.relatedType(this).toString()))
                 .reduce(HsHostingAssetType::onlyASingleElementExpectedException)
                 .orElse(null);
     }
 
     public RelationPolicy parentAssetPolicy() {
-        return stream(relations).filter(r -> r.relatedType instanceof HsHostingAssetType)
-                .map(r -> r.relationType)
+        return stream(relations)
+                .filter(r -> r.relationType == PARENT_ASSET)
+                .map(r -> r.relationPolicy)
                 .reduce(HsHostingAssetType::onlyASingleElementExpectedException)
                 .orElse(RelationPolicy.FORBIDDEN);
     }
 
     public HsHostingAssetType parentAssetType() {
-        return stream(relations).filter(r -> r.relatedType instanceof HsHostingAssetType)
-                .map(r -> HsHostingAssetType.valueOf(r.relatedType.toString()))
+        return stream(relations)
+                .filter(r -> r.relationType == PARENT_ASSET)
+                .map(r -> HsHostingAssetType.valueOf(r.relatedType(this).toString()))
                 .reduce(HsHostingAssetType::onlyASingleElementExpectedException)
                 .orElse(null);
     }
 
     public RelationPolicy assignedToAssetPolicy() {
-        return stream(relations).filter(r -> r.relatedType == (Object) HsHostingAssetType.class)
-                .map(r -> r.relationType)
+        return stream(relations)
+                .filter(r -> r.relationType == ASSIGNED_TO_ASSET)
+                .map(r -> r.relationPolicy)
                 .reduce(HsHostingAssetType::onlyASingleElementExpectedException)
                 .orElse(RelationPolicy.FORBIDDEN);
     }
 
     public HsHostingAssetType assignedToAssetType() {
-        return stream(relations).filter(r -> r.relatedType == (Object) HsHostingAssetType.class)
-                .map(r -> HsHostingAssetType.valueOf(r.relatedType.toString()))
+        return stream(relations)
+                .filter(r -> r.relationType == ASSIGNED_TO_ASSET)
+                .map(r -> HsHostingAssetType.valueOf(r.relatedType(this).toString()))
                 .reduce(HsHostingAssetType::onlyASingleElementExpectedException)
                 .orElse(null);
     }
@@ -183,14 +192,10 @@ public enum HsHostingAssetType implements Node {
     @Override
     public List<String> edges() {
         return stream(relations)
-                .map(r -> nodeName() + r.edge + resolveNode(r.relatedType).nodeName())
+                .map(r -> nodeName() + r.edge + r.relatedType(this).nodeName())
                 .toList();
     }
 
-    private Node resolveNode(final Node node) {
-        return node == SAME_TYPE ? this : node;
-    }
-
     @Override
     public String nodeName() {
         return "HA_" + name();
@@ -310,28 +315,41 @@ public enum HsHostingAssetType implements Node {
     public enum RelationPolicy {
         FORBIDDEN, OPTIONAL, REQUIRED
     }
+
+    public enum RelationType {
+        BOOKING_ITEM,
+                PARENT_ASSET,
+                ASSIGNED_TO_ASSET
+    }
 }
 
 @AllArgsConstructor
 class EntityTypeRelation<E, T extends Node> {
-    final HsHostingAssetType.RelationPolicy relationType;
+
+    final HsHostingAssetType.RelationPolicy relationPolicy;
+    final HsHostingAssetType.RelationType relationType;
     final Function<HsHostingAssetEntity, E> getter;
-    final T relatedType;
+    private final T relatedType;
     final String edge;
 
+    public T relatedType(final HsHostingAssetType referringType) {
+        //noinspection unchecked
+        return relatedType == HsHostingAssetType.SAME_TYPE ? (T) referringType : relatedType;
+    }
+
     static EntityTypeRelation<HsBookingItemEntity, HsBookingItemType> requires(final HsBookingItemType bookingItemType) {
-        return new EntityTypeRelation<>(REQUIRED, HsHostingAssetEntity::getBookingItem, bookingItemType, " *==> ");
+        return new EntityTypeRelation<>(REQUIRED, BOOKING_ITEM, HsHostingAssetEntity::getBookingItem, bookingItemType, " *==> ");
     }
 
     static EntityTypeRelation<HsHostingAssetEntity, HsHostingAssetType> optionalParent(final HsHostingAssetType hostingAssetType) {
-        return new EntityTypeRelation<>(OPTIONAL, HsHostingAssetEntity::getParentAsset, hostingAssetType, " o..> ");
+        return new EntityTypeRelation<>(OPTIONAL, PARENT_ASSET, HsHostingAssetEntity::getParentAsset, hostingAssetType, " o..> ");
     }
 
     static EntityTypeRelation<HsHostingAssetEntity, HsHostingAssetType> requiredParent(final HsHostingAssetType hostingAssetType) {
-        return new EntityTypeRelation<>(REQUIRED, HsHostingAssetEntity::getParentAsset, hostingAssetType, " *==> ");
+        return new EntityTypeRelation<>(REQUIRED, PARENT_ASSET, HsHostingAssetEntity::getParentAsset, hostingAssetType, " *==> ");
     }
 
     static EntityTypeRelation<HsHostingAssetEntity, HsHostingAssetType> assignedTo(final HsHostingAssetType hostingAssetType) {
-        return new EntityTypeRelation<>(REQUIRED, HsHostingAssetEntity::getAssignedToAsset, hostingAssetType, " o..> ");
+        return new EntityTypeRelation<>(REQUIRED, ASSIGNED_TO_ASSET, HsHostingAssetEntity::getAssignedToAsset, hostingAssetType, " o..> ");
     }
 }
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsDomainDnsSetupHostingAssetValidator.java b/src/main/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsDomainDnsSetupHostingAssetValidator.java
index eea095fb..c263be60 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsDomainDnsSetupHostingAssetValidator.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsDomainDnsSetupHostingAssetValidator.java
@@ -60,7 +60,7 @@ class HsDomainDnsSetupHostingAssetValidator extends HsHostingAssetEntityValidato
 
     @Override
     protected Pattern identifierPattern(final HsHostingAssetEntity assetEntity) {
-        return  Pattern.compile("^" + assetEntity.getParentAsset().getIdentifier() + IDENTIFIER_SUFFIX + "$");
+        return  Pattern.compile("^" + assetEntity.getParentAsset().getIdentifier() + Pattern.quote(IDENTIFIER_SUFFIX) + "$");
     }
 
     @Override
diff --git a/src/main/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsHostingAssetEntityValidator.java b/src/main/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsHostingAssetEntityValidator.java
index 53858c29..187630fb 100644
--- a/src/main/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsHostingAssetEntityValidator.java
+++ b/src/main/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsHostingAssetEntityValidator.java
@@ -20,9 +20,6 @@ import java.util.stream.Stream;
 import static java.util.Arrays.stream;
 import static java.util.Collections.emptyList;
 import static java.util.Optional.ofNullable;
-import static net.hostsharing.hsadminng.hs.hosting.asset.HsHostingAssetType.RelationPolicy.FORBIDDEN;
-import static net.hostsharing.hsadminng.hs.hosting.asset.HsHostingAssetType.RelationPolicy.OPTIONAL;
-import static net.hostsharing.hsadminng.hs.hosting.asset.HsHostingAssetType.RelationPolicy.REQUIRED;
 
 public abstract class HsHostingAssetEntityValidator extends HsEntityValidator<HsHostingAssetEntity> {
 
@@ -34,7 +31,9 @@ public abstract class HsHostingAssetEntityValidator extends HsEntityValidator<Hs
     private final HsHostingAssetEntityValidator.AlarmContact alarmContactValidation;
 
     HsHostingAssetEntityValidator(
-            final HsHostingAssetType assetType, final AlarmContact alarmContactValidation, final ValidatableProperty<?, ?>... properties) {
+            final HsHostingAssetType assetType,
+            final AlarmContact alarmContactValidation,
+            final ValidatableProperty<?, ?>... properties) {
         super(properties);
         this.bookingItemReferenceValidation = new ReferenceValidator<>(
                 assetType.bookingItemPolicy(),
@@ -73,11 +72,11 @@ public abstract class HsHostingAssetEntityValidator extends HsEntityValidator<Hs
 
     private List<String> validateEntityReferencesAndProperties(final HsHostingAssetEntity assetEntity) {
         return Stream.of(
-                    validateReferencedEntity(assetEntity, "bookingItem", bookingItemReferenceValidation::validate),
-                    validateReferencedEntity(assetEntity, "parentAsset", parentAssetReferenceValidation::validate),
-                    validateReferencedEntity(assetEntity, "assignedToAsset", assignedToAssetReferenceValidation::validate),
-                    validateReferencedEntity(assetEntity, "alarmContact", alarmContactValidation::validate),
-                    validateProperties(assetEntity))
+                        validateReferencedEntity(assetEntity, "bookingItem", bookingItemReferenceValidation::validate),
+                        validateReferencedEntity(assetEntity, "parentAsset", parentAssetReferenceValidation::validate),
+                        validateReferencedEntity(assetEntity, "assignedToAsset", assignedToAssetReferenceValidation::validate),
+                        validateReferencedEntity(assetEntity, "alarmContact", alarmContactValidation::validate),
+                        validateProperties(assetEntity))
                 .filter(Objects::nonNull)
                 .flatMap(List::stream)
                 .filter(Objects::nonNull)
@@ -97,25 +96,28 @@ public abstract class HsHostingAssetEntityValidator extends HsEntityValidator<Hs
 
     private static List<String> optionallyValidate(final HsHostingAssetEntity assetEntity) {
         return assetEntity != null
-                ? enrich(prefix(assetEntity.toShortString(), "parentAsset"),
-                        HsHostingAssetEntityValidatorRegistry.forType(assetEntity.getType()).validateContext(assetEntity))
+                ? enrich(
+                    prefix(assetEntity.toShortString(), "parentAsset"),
+                    HsHostingAssetEntityValidatorRegistry.forType(assetEntity.getType()).validateContext(assetEntity))
                 : emptyList();
     }
 
     private static List<String> optionallyValidate(final HsBookingItemEntity bookingItem) {
         return bookingItem != null
-                ? enrich(prefix(bookingItem.toShortString(), "bookingItem"),
-                    HsBookingItemEntityValidatorRegistry.forType(bookingItem.getType()).validateContext(bookingItem))
+                ? enrich(
+                prefix(bookingItem.toShortString(), "bookingItem"),
+                HsBookingItemEntityValidatorRegistry.forType(bookingItem.getType()).validateContext(bookingItem))
                 : emptyList();
     }
 
     protected List<String> validateAgainstSubEntities(final HsHostingAssetEntity assetEntity) {
-        return enrich(prefix(assetEntity.toShortString(), "config"),
+        return enrich(
+                prefix(assetEntity.toShortString(), "config"),
                 stream(propertyValidators)
-                    .filter(ValidatableProperty::isTotalsValidator)
-                    .map(prop -> validateMaxTotalValue(assetEntity, prop))
-                    .filter(Objects::nonNull)
-                    .toList());
+                        .filter(ValidatableProperty::isTotalsValidator)
+                        .map(prop -> validateMaxTotalValue(assetEntity, prop))
+                        .filter(Objects::nonNull)
+                        .toList());
     }
 
     // TODO.test: check, if there are any hosting assets which need this validation at all
@@ -140,7 +142,9 @@ public abstract class HsHostingAssetEntityValidator extends HsEntityValidator<Hs
         final var expectedIdentifierPattern = identifierPattern(assetEntity);
         if (assetEntity.getIdentifier() == null ||
                 !expectedIdentifierPattern.matcher(assetEntity.getIdentifier()).matches()) {
-            return List.of("'identifier' expected to match '"+expectedIdentifierPattern+"', but is '" + assetEntity.getIdentifier() + "'");
+            return List.of(
+                    "'identifier' expected to match '" + expectedIdentifierPattern + "', but is '" + assetEntity.getIdentifier()
+                            + "'");
         }
         return Collections.emptyList();
     }
@@ -150,42 +154,54 @@ public abstract class HsHostingAssetEntityValidator extends HsEntityValidator<Hs
     static class ReferenceValidator<S, T> {
 
         private final HsHostingAssetType.RelationPolicy policy;
-        private final T subEntityType;
-        private final Function<HsHostingAssetEntity, S> subEntityGetter;
-        private final Function<S,T> subEntityTypeGetter;
+        private final T referencedEntityType;
+        private final Function<HsHostingAssetEntity, S> referencedEntityGetter;
+        private final Function<S, T> referencedEntityTypeGetter;
 
         public ReferenceValidator(
                 final HsHostingAssetType.RelationPolicy policy,
                 final T subEntityType,
-                final Function<HsHostingAssetEntity, S> subEntityGetter,
-                final Function<S, T> subEntityTypeGetter) {
+                final Function<HsHostingAssetEntity, S> referencedEntityGetter,
+                final Function<S, T> referencedEntityTypeGetter) {
             this.policy = policy;
-            this.subEntityType = subEntityType;
-            this.subEntityGetter = subEntityGetter;
-            this.subEntityTypeGetter = subEntityTypeGetter;
+            this.referencedEntityType = subEntityType;
+            this.referencedEntityGetter = referencedEntityGetter;
+            this.referencedEntityTypeGetter = referencedEntityTypeGetter;
         }
 
         public ReferenceValidator(
                 final HsHostingAssetType.RelationPolicy policy,
-                final Function<HsHostingAssetEntity, S> subEntityGetter) {
+                final Function<HsHostingAssetEntity, S> referencedEntityGetter) {
             this.policy = policy;
-            this.subEntityType = null;
-            this.subEntityGetter = subEntityGetter;
-            this.subEntityTypeGetter = e -> null;
+            this.referencedEntityType = null;
+            this.referencedEntityGetter = referencedEntityGetter;
+            this.referencedEntityTypeGetter = e -> null;
         }
 
         List<String> validate(final HsHostingAssetEntity assetEntity, final String referenceFieldName) {
 
-            final var subEntity = subEntityGetter.apply(assetEntity);
-            if (policy == REQUIRED && subEntity == null) {
-                return List.of(referenceFieldName + "' must not be null but is null");
-            }
-            if ((policy == FORBIDDEN) && (subEntity != null)) {
-                return List.of(referenceFieldName + "' must be null but is set to "+ assetEntity.getBookingItem().toShortString());
-            }
-            final var subItemType = subEntity != null ? subEntityTypeGetter.apply(subEntity) : null;
-            if (policy != OPTIONAL && subEntityType != null && subItemType != subEntityType) {
-                return List.of(referenceFieldName + "' must be of type " + subEntityType + " but is of type " + subItemType);
+            final var actualEntity = referencedEntityGetter.apply(assetEntity);
+            final var actualEntityType = actualEntity != null ? referencedEntityTypeGetter.apply(actualEntity) : null;
+
+            switch (policy) {
+            case REQUIRED:
+                if (actualEntityType != referencedEntityType) {
+                    return List.of(actualEntityType == null
+                            ? referenceFieldName + "' must be of type " + referencedEntityType + " but is null"
+                            : referenceFieldName + "' must be of type " + referencedEntityType + " but is of type " + actualEntityType);
+                }
+                break;
+            case OPTIONAL:
+                if (actualEntityType != null && actualEntityType != referencedEntityType) {
+                    return List.of(referenceFieldName + "' must be null or of type " + referencedEntityType + " but is of type "
+                            + actualEntityType);
+                }
+                break;
+            case FORBIDDEN:
+                if (actualEntityType != null) {
+                    return List.of(referenceFieldName + "' must be null but is of type " + actualEntityType);
+                }
+                break;
             }
             return emptyList();
         }
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/HsHostingAssetControllerRestTest.java b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/HsHostingAssetControllerRestTest.java
index 8cd2eb3f..eed85585 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/HsHostingAssetControllerRestTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/HsHostingAssetControllerRestTest.java
@@ -186,6 +186,24 @@ public class HsHostingAssetControllerRestTest {
                         }
                     ]
                 """),
+        DOMAIN_SETUP(
+                List.of(
+                        HsHostingAssetEntity.builder()
+                                .type(HsHostingAssetType.DOMAIN_SETUP)
+                                .identifier("example.org")
+                                .caption("some fake Domain-Setup")
+                                .build()),
+                """
+                    [
+                        {
+                            "type": "DOMAIN_SETUP",
+                            "identifier": "example.org",
+                            "caption": "some fake Domain-Setup",
+                            "alarmContact": null,
+                            "config": {}
+                        }
+                    ]
+                """),
         DOMAIN_DNS_SETUP(
                 List.of(
                         HsHostingAssetEntity.builder()
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsCloudServerHostingAssetValidatorUnitTest.java b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsCloudServerHostingAssetValidatorUnitTest.java
index 69fe01bb..8361c5f4 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsCloudServerHostingAssetValidatorUnitTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsCloudServerHostingAssetValidatorUnitTest.java
@@ -33,7 +33,7 @@ class HsCloudServerHostingAssetValidatorUnitTest {
 
         // then
         assertThat(result).containsExactlyInAnyOrder(
-                "'CLOUD_SERVER:vm1234.bookingItem' must not be null but is null",
+                "'CLOUD_SERVER:vm1234.bookingItem' must be of type CLOUD_SERVER but is null",
                 "'CLOUD_SERVER:vm1234.config.RAM' is not expected but is set to '2000'");
     }
 
@@ -84,14 +84,14 @@ class HsCloudServerHostingAssetValidatorUnitTest {
     }
 
     @Test
-    void validatesParentAndAssignedToAssetMustNotBeSet() {
+    void rejectsInvalidReferencedEntities() {
         // given
         final var mangedServerHostingAssetEntity = HsHostingAssetEntity.builder()
                 .type(CLOUD_SERVER)
-                .identifier("xyz00")
-                .parentAsset(HsHostingAssetEntity.builder().build())
-                .assignedToAsset(HsHostingAssetEntity.builder().build())
+                .identifier("vm1234")
                 .bookingItem(HsBookingItemEntity.builder().type(HsBookingItemType.CLOUD_SERVER).build())
+                .parentAsset(HsHostingAssetEntity.builder().type(MANAGED_SERVER).build())
+                .assignedToAsset(HsHostingAssetEntity.builder().type(CLOUD_SERVER).build())
                 .build();
         final var validator = HsHostingAssetEntityValidatorRegistry.forType(mangedServerHostingAssetEntity.getType());
 
@@ -100,7 +100,7 @@ class HsCloudServerHostingAssetValidatorUnitTest {
 
         // then
         assertThat(result).containsExactlyInAnyOrder(
-                "'CLOUD_SERVER:xyz00.parentAsset' must be null but is set to D-???????-?:null",
-                "'CLOUD_SERVER:xyz00.assignedToAsset' must be null but is set to D-???????-?:null");
+                "'CLOUD_SERVER:vm1234.parentAsset' must be null but is of type MANAGED_SERVER",
+                "'CLOUD_SERVER:vm1234.assignedToAsset' must be null but is of type CLOUD_SERVER");
     }
 }
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsDomainDnsSetupHostingAssetValidatorUnitTest.java b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsDomainDnsSetupHostingAssetValidatorUnitTest.java
index 6a4e1026..681196ae 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsDomainDnsSetupHostingAssetValidatorUnitTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsDomainDnsSetupHostingAssetValidatorUnitTest.java
@@ -95,7 +95,7 @@ class HsDomainDnsSetupHostingAssetValidatorUnitTest {
 
         // then
         assertThat(result).containsExactly(
-                "'identifier' expected to match '^example.org|DNS$', but is 'example.org'"
+                "'identifier' expected to match '^example.org\\Q|DNS\\E$', but is 'example.org'"
         );
     }
 
@@ -113,12 +113,12 @@ class HsDomainDnsSetupHostingAssetValidatorUnitTest {
     }
 
     @Test
-    void validatesReferencedEntities() {
+    void rejectsInvalidReferencedEntities() {
         // given
         final var mangedServerHostingAssetEntity = validEntityBuilder()
-                .parentAsset(HsHostingAssetEntity.builder().build())
-                .assignedToAsset(HsHostingAssetEntity.builder().build())
                 .bookingItem(HsBookingItemEntity.builder().type(HsBookingItemType.CLOUD_SERVER).build())
+                .parentAsset(null)
+                .assignedToAsset(HsHostingAssetEntity.builder().type(DOMAIN_SETUP).build())
                 .build();
         final var validator = HsHostingAssetEntityValidatorRegistry.forType(mangedServerHostingAssetEntity.getType());
 
@@ -127,9 +127,9 @@ class HsDomainDnsSetupHostingAssetValidatorUnitTest {
 
         // then
         assertThat(result).containsExactlyInAnyOrder(
-                "'DOMAIN_DNS_SETUP:example.org|DNS.bookingItem' must be null but is set to D-???????-?:null",
-                "'DOMAIN_DNS_SETUP:example.org|DNS.parentAsset' must be of type DOMAIN_SETUP but is of type null",
-                "'DOMAIN_DNS_SETUP:example.org|DNS.assignedToAsset' must be null but is set to D-???????-?:null");
+                "'DOMAIN_DNS_SETUP:example.org|DNS.bookingItem' must be null but is of type CLOUD_SERVER",
+                "'DOMAIN_DNS_SETUP:example.org|DNS.parentAsset' must be of type DOMAIN_SETUP but is null",
+                "'DOMAIN_DNS_SETUP:example.org|DNS.assignedToAsset' must be null but is of type DOMAIN_SETUP");
     }
 
     @Test
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsDomainSetupHostingAssetValidatorUnitTest.java b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsDomainSetupHostingAssetValidatorUnitTest.java
new file mode 100644
index 00000000..c9b99784
--- /dev/null
+++ b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsDomainSetupHostingAssetValidatorUnitTest.java
@@ -0,0 +1,112 @@
+package net.hostsharing.hsadminng.hs.hosting.asset.validators;
+
+import net.hostsharing.hsadminng.hs.booking.item.HsBookingItemEntity;
+import net.hostsharing.hsadminng.hs.booking.item.HsBookingItemType;
+import net.hostsharing.hsadminng.hs.hosting.asset.HsHostingAssetEntity;
+import net.hostsharing.hsadminng.hs.hosting.asset.HsHostingAssetEntity.HsHostingAssetEntityBuilder;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.EnumSource;
+
+import java.util.Map;
+
+import static net.hostsharing.hsadminng.hs.hosting.asset.HsHostingAssetType.CLOUD_SERVER;
+import static net.hostsharing.hsadminng.hs.hosting.asset.HsHostingAssetType.DOMAIN_SETUP;
+import static net.hostsharing.hsadminng.hs.hosting.asset.HsHostingAssetType.MANAGED_SERVER;
+import static org.assertj.core.api.Assertions.assertThat;
+
+class HsDomainSetupHostingAssetValidatorUnitTest {
+
+    static HsHostingAssetEntityBuilder validEntityBuilder() {
+        return HsHostingAssetEntity.builder()
+                .type(DOMAIN_SETUP)
+                .identifier("example.org");
+    }
+
+    enum InvalidDomainNameIdentifier {
+        EMPTY(""),
+        TOO_LONG("abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz0123456890123456789.de"),
+        DASH_AT_BEGINNING("-example.com"),
+        DOT_AT_BEGINNING(".example.com"),
+        DOT_AT_END("example.com.");
+
+        final String domainName;
+
+        InvalidDomainNameIdentifier(final String domainName) {
+            this.domainName = domainName;
+        }
+    }
+
+    @ParameterizedTest
+    @EnumSource(InvalidDomainNameIdentifier.class)
+    void rejectsInvalidIdentifier(final InvalidDomainNameIdentifier testCase) {
+        // given
+        final var givenEntity = validEntityBuilder().identifier(testCase.domainName).build();
+        final var validator = HsHostingAssetEntityValidatorRegistry.forType(givenEntity.getType());
+
+        // when
+        final var result = validator.validateEntity(givenEntity);
+
+        // then
+        assertThat(result).containsExactly(
+                "'identifier' expected to match '^((?!-)[A-Za-z0-9-]{1,63}(?<!-)\\.)+[A-Za-z]{2,6}', but is '"+testCase.domainName+"'"
+        );
+    }
+
+
+    enum ValidDomainNameIdentifier {
+        SIMPLE("exampe.org"),
+        MAX_LENGTH("abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz01234568901.de"),
+        WITH_DASH("example-test.com"),
+        SUBDOMAIN("test.example.com");
+
+        final String domainName;
+
+        ValidDomainNameIdentifier(final String domainName) {
+            this.domainName = domainName;
+        }
+    }
+
+    @ParameterizedTest
+    @EnumSource(ValidDomainNameIdentifier.class)
+    void acceptsValidIdentifier(final ValidDomainNameIdentifier testCase) {
+        // given
+        final var givenEntity = validEntityBuilder().identifier(testCase.domainName).build();
+        final var validator = HsHostingAssetEntityValidatorRegistry.forType(givenEntity.getType());
+
+        // when
+        final var result = validator.validateEntity(givenEntity);
+
+        // then
+        assertThat(result).isEmpty();
+    }
+
+    @Test
+    void containsNoProperties() {
+        // when
+        final var validator = HsHostingAssetEntityValidatorRegistry.forType(CLOUD_SERVER);
+
+        // then
+        assertThat(validator.properties()).map(Map::toString).isEmpty();
+    }
+
+    @Test
+    void validatesReferencedEntities() {
+        // given
+        final var mangedServerHostingAssetEntity = validEntityBuilder()
+                .parentAsset(HsHostingAssetEntity.builder().type(CLOUD_SERVER).build())
+                .assignedToAsset(HsHostingAssetEntity.builder().type(MANAGED_SERVER).build())
+                .bookingItem(HsBookingItemEntity.builder().type(HsBookingItemType.CLOUD_SERVER).build())
+                .build();
+        final var validator = HsHostingAssetEntityValidatorRegistry.forType(mangedServerHostingAssetEntity.getType());
+
+        // when
+        final var result = validator.validateEntity(mangedServerHostingAssetEntity);
+
+        // then
+        assertThat(result).containsExactlyInAnyOrder(
+                "'DOMAIN_SETUP:example.org.bookingItem' must be null but is of type CLOUD_SERVER",
+                "'DOMAIN_SETUP:example.org.parentAsset' must be null or of type DOMAIN_SETUP but is of type CLOUD_SERVER",
+                "'DOMAIN_SETUP:example.org.assignedToAsset' must be null but is of type MANAGED_SERVER");
+    }
+}
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsEMailAliasHostingAssetValidatorUnitTest.java b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsEMailAliasHostingAssetValidatorUnitTest.java
index 6c35078b..38e7564e 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsEMailAliasHostingAssetValidatorUnitTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsEMailAliasHostingAssetValidatorUnitTest.java
@@ -107,8 +107,8 @@ class HsEMailAliasHostingAssetValidatorUnitTest {
 
         // then
         assertThat(result).containsExactlyInAnyOrder(
-                "'EMAIL_ALIAS:abc00-office.bookingItem' must be null but is set to D-1234500:test project:test project booking item",
+                "'EMAIL_ALIAS:abc00-office.bookingItem' must be null but is of type MANAGED_SERVER",
                 "'EMAIL_ALIAS:abc00-office.parentAsset' must be of type MANAGED_WEBSPACE but is of type MANAGED_SERVER",
-                "'EMAIL_ALIAS:abc00-office.assignedToAsset' must be null but is set to D-1234500:test project:test project booking item");
+                "'EMAIL_ALIAS:abc00-office.assignedToAsset' must be null but is of type MANAGED_SERVER");
     }
 }
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsManagedServerHostingAssetValidatorUnitTest.java b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsManagedServerHostingAssetValidatorUnitTest.java
index fd8d4800..15b2ca97 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsManagedServerHostingAssetValidatorUnitTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsManagedServerHostingAssetValidatorUnitTest.java
@@ -10,6 +10,7 @@ import java.util.Map;
 import static java.util.Map.entry;
 import static net.hostsharing.hsadminng.hs.booking.item.TestHsBookingItem.TEST_CLOUD_SERVER_BOOKING_ITEM;
 import static net.hostsharing.hsadminng.hs.booking.item.TestHsBookingItem.TEST_MANAGED_SERVER_BOOKING_ITEM;
+import static net.hostsharing.hsadminng.hs.hosting.asset.HsHostingAssetType.CLOUD_SERVER;
 import static net.hostsharing.hsadminng.hs.hosting.asset.HsHostingAssetType.MANAGED_SERVER;
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -22,8 +23,8 @@ class HsManagedServerHostingAssetValidatorUnitTest {
                 .type(MANAGED_SERVER)
                 .identifier("vm1234")
                 .bookingItem(TEST_MANAGED_SERVER_BOOKING_ITEM)
-                .parentAsset(HsHostingAssetEntity.builder().build())
-                .assignedToAsset(HsHostingAssetEntity.builder().build())
+                .parentAsset(HsHostingAssetEntity.builder().type(CLOUD_SERVER).build())
+                .assignedToAsset(HsHostingAssetEntity.builder().type(CLOUD_SERVER).build())
                 .config(Map.ofEntries(
                         entry("monit_max_hdd_usage", "90"),
                         entry("monit_max_cpu_usage", 2),
@@ -37,8 +38,8 @@ class HsManagedServerHostingAssetValidatorUnitTest {
 
         // then
         assertThat(result).containsExactlyInAnyOrder(
-                "'MANAGED_SERVER:vm1234.parentAsset' must be null but is set to D-1234500:test project:test project booking item",
-                "'MANAGED_SERVER:vm1234.assignedToAsset' must be null but is set to D-1234500:test project:test project booking item",
+                "'MANAGED_SERVER:vm1234.parentAsset' must be null but is of type CLOUD_SERVER",
+                "'MANAGED_SERVER:vm1234.assignedToAsset' must be null but is of type CLOUD_SERVER",
                 "'MANAGED_SERVER:vm1234.config.monit_max_cpu_usage' is expected to be at least 10 but is 2",
                 "'MANAGED_SERVER:vm1234.config.monit_max_ram_usage' is expected to be at most 100 but is 101",
                 "'MANAGED_SERVER:vm1234.config.monit_max_hdd_usage' is expected to be of type class java.lang.Integer, but is of type 'String'");
@@ -63,14 +64,14 @@ class HsManagedServerHostingAssetValidatorUnitTest {
     }
 
     @Test
-    void validatesParentAndAssignedToAssetMustNotBeSet() {
+    void rejectsInvalidReferencedEntities() {
         // given
         final var mangedServerHostingAssetEntity = HsHostingAssetEntity.builder()
                 .type(MANAGED_SERVER)
                 .identifier("xyz00")
-                .parentAsset(HsHostingAssetEntity.builder().build())
-                .assignedToAsset(HsHostingAssetEntity.builder().build())
                 .bookingItem(TEST_CLOUD_SERVER_BOOKING_ITEM)
+                .parentAsset(HsHostingAssetEntity.builder().type(CLOUD_SERVER).build())
+                .assignedToAsset(HsHostingAssetEntity.builder().type(MANAGED_SERVER).build())
                 .build();
         final var validator = HsHostingAssetEntityValidatorRegistry.forType(mangedServerHostingAssetEntity.getType());
 
@@ -80,7 +81,7 @@ class HsManagedServerHostingAssetValidatorUnitTest {
         // then
         assertThat(result).containsExactlyInAnyOrder(
                 "'MANAGED_SERVER:xyz00.bookingItem' must be of type MANAGED_SERVER but is of type CLOUD_SERVER",
-                "'MANAGED_SERVER:xyz00.parentAsset' must be null but is set to D-1234500:test project:test cloud server booking item",
-                "'MANAGED_SERVER:xyz00.assignedToAsset' must be null but is set to D-1234500:test project:test cloud server booking item");
+                "'MANAGED_SERVER:xyz00.parentAsset' must be null but is of type CLOUD_SERVER",
+                "'MANAGED_SERVER:xyz00.assignedToAsset' must be null but is of type MANAGED_SERVER");
     }
 }
diff --git a/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsManagedWebspaceHostingAssetValidatorUnitTest.java b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsManagedWebspaceHostingAssetValidatorUnitTest.java
index 1d2c6d24..7e353147 100644
--- a/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsManagedWebspaceHostingAssetValidatorUnitTest.java
+++ b/src/test/java/net/hostsharing/hsadminng/hs/hosting/asset/validators/HsManagedWebspaceHostingAssetValidatorUnitTest.java
@@ -10,6 +10,7 @@ import java.util.Map;
 import java.util.stream.Stream;
 
 import static java.util.Map.entry;
+import static net.hostsharing.hsadminng.hs.hosting.asset.HsHostingAssetType.CLOUD_SERVER;
 import static net.hostsharing.hsadminng.hs.hosting.asset.HsHostingAssetType.MANAGED_WEBSPACE;
 import static org.assertj.core.api.Assertions.assertThat;
 import static net.hostsharing.hsadminng.hs.booking.project.TestHsBookingProject.TEST_PROJECT;
@@ -142,7 +143,7 @@ class HsManagedWebspaceHostingAssetValidatorUnitTest {
     }
 
     @Test
-    void validatesEntityReferences() {
+    void rejectsInvalidEntityReferences() {
         // given
         final var validator = HsHostingAssetEntityValidatorRegistry.forType(MANAGED_WEBSPACE);
         final var mangedWebspaceHostingAssetEntity = HsHostingAssetEntity.builder()
@@ -153,7 +154,7 @@ class HsManagedWebspaceHostingAssetValidatorUnitTest {
                         .resources(Map.ofEntries(entry("SSD", 25), entry("Traffic", 250)))
                         .build())
                 .parentAsset(cloudServerAssetEntity)
-                .assignedToAsset(HsHostingAssetEntity.builder().build())
+                .assignedToAsset(HsHostingAssetEntity.builder().type(CLOUD_SERVER).build())
                 .identifier("abc00")
                 .build();
 
@@ -163,7 +164,7 @@ class HsManagedWebspaceHostingAssetValidatorUnitTest {
         // then
         assertThat(result).containsExactly(
                 "'MANAGED_WEBSPACE:abc00.bookingItem' must be of type MANAGED_WEBSPACE but is of type MANAGED_SERVER",
-                "'MANAGED_WEBSPACE:abc00.parentAsset' must be of type MANAGED_SERVER but is of type CLOUD_SERVER",
-                "'MANAGED_WEBSPACE:abc00.assignedToAsset' must be null but is set to D-???????-?:some ManagedServer");
+                "'MANAGED_WEBSPACE:abc00.parentAsset' must be null or of type MANAGED_SERVER but is of type CLOUD_SERVER",
+                "'MANAGED_WEBSPACE:abc00.assignedToAsset' must be null but is of type CLOUD_SERVER");
     }
 }
diff --git a/src/test/java/net/hostsharing/hsadminng/rbac/test/ContextBasedTestWithCleanup.java b/src/test/java/net/hostsharing/hsadminng/rbac/test/ContextBasedTestWithCleanup.java
index 14e8619a..5e9d8347 100644
--- a/src/test/java/net/hostsharing/hsadminng/rbac/test/ContextBasedTestWithCleanup.java
+++ b/src/test/java/net/hostsharing/hsadminng/rbac/test/ContextBasedTestWithCleanup.java
@@ -8,6 +8,7 @@ import net.hostsharing.hsadminng.rbac.rbacgrant.RbacGrantsDiagramService;
 import net.hostsharing.hsadminng.rbac.rbacrole.RbacRoleEntity;
 import net.hostsharing.hsadminng.rbac.rbacrole.RbacRoleRepository;
 import org.jetbrains.annotations.NotNull;
+import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.TestInfo;
 import org.springframework.beans.factory.annotation.Autowired;
@@ -170,7 +171,7 @@ public abstract class ContextBasedTestWithCleanup extends ContextBasedTest {
         this.testInfo = testInfo;
     }
 
-    //@AfterEach
+    @AfterEach
     void cleanupAndCheckCleanup(final TestInfo testInfo) {
         // If the whole test method has its own transaction, cleanup makes no sense.
         // If that transaction even failed, cleaunup would cause an exception.