diff --git a/networks/tests/test_dhcp_range.py b/networks/tests/test_dhcp_range.py
new file mode 100644
index 00000000..42e07690
--- /dev/null
+++ b/networks/tests/test_dhcp_range.py
@@ -0,0 +1,64 @@
+"""A network's DHCP range is changed while the network is stopped, and the
+page says so only when it was: a running network, a network without a
+range or an unknown address family is refused with the reason. Runs on a
+private libvirt test driver: "test:///default" is shared by the whole
+process."""
+
+import tempfile
+from unittest.mock import patch
+
+import libvirt
+from computes.models import Compute
+from django.contrib.auth import get_user_model
+from django.contrib.messages import get_messages
+from django.test import TestCase
+from django.urls import reverse
+from lxml import etree
+
+NODE = """<node>
+  <network><name>lab</name><bridge name='virbr9'/>
+    <ip address='192.0.2.1' netmask='255.255.255.0'><dhcp><range start='192.0.2.10' end='192.0.2.20'/></dhcp></ip>
+  </network>
+  <network><name>plain</name><bridge name='virbr8'/><ip address='198.51.100.1' netmask='255.255.255.0'/></network>
+</node>"""
+
+
+class DhcpRangeTests(TestCase):
+    def setUp(self):
+        node = tempfile.NamedTemporaryFile("w", suffix=".xml")
+        self.addCleanup(node.close)
+        node.write(NODE)
+        node.flush()
+        self.conn = libvirt.open(f"test://{node.name}")
+        self.addCleanup(self.conn.close)
+        patcher = patch("vrtManager.connection.connection_manager.get_connection", return_value=self.conn)
+        patcher.start()
+        self.addCleanup(patcher.stop)
+        self.compute = Compute.objects.create(name="dhcp", hostname="localhost", login="", password="", type=4)
+        self.client.force_login(get_user_model().objects.create_superuser("dhcp", "dhcp@example.com", "pw"))
+
+    def change(self, network, family="ipv4"):
+        response = self.client.post(reverse("network", args=[self.compute.id, network]), {
+            "modify_dhcp_range": "", "range_start": "192.0.2.30", "range_end": "192.0.2.40", "family": family})
+        return [str(m) for m in get_messages(response.wsgi_request)]
+
+    def dhcp_range(self, network):
+        xml = etree.fromstring(self.conn.networkLookupByName(network).XMLDesc(0))
+        return xml.xpath("ip/dhcp/range/@start|ip/dhcp/range/@end")
+
+    def test_a_stopped_network_gets_the_new_range(self):
+        self.conn.networkLookupByName("lab").destroy()
+        self.assertEqual(self.change("lab"), ["IPV4 DHCP Range is Changed."])
+        self.assertEqual(self.dhcp_range("lab"), ["192.0.2.30", "192.0.2.40"])
+
+    def test_a_running_network_is_refused(self):
+        messages = self.change("lab")
+        self.assertEqual(messages, ["Stop network lab to change its DHCP range"])
+        self.assertEqual(self.dhcp_range("lab"), ["192.0.2.10", "192.0.2.20"])
+
+    def test_a_network_without_a_range_or_an_unknown_family_is_refused(self):
+        self.conn.networkLookupByName("lab").destroy()
+        self.conn.networkLookupByName("plain").destroy()
+        self.assertEqual(self.change("plain"), ["Network plain has no ipv4 DHCP range"])
+        self.assertEqual(self.change("lab", family="ipx"), ["Network lab has no ipx DHCP range"])
+        self.assertEqual(self.dhcp_range("lab"), ["192.0.2.10", "192.0.2.20"])
diff --git a/vrtManager/network.py b/vrtManager/network.py
index 646333e7..0044b7c1 100644
--- a/vrtManager/network.py
+++ b/vrtManager/network.py
@@ -267,15 +267,17 @@ class wvmNetwork(wvmConnect):
                 return result
 
     def modify_dhcp_range(self, range_start, range_end, family="ipv4"):
-        if not self.is_active():
-            tree = etree.fromstring(self._XMLDesc(0))
-            if family == "ipv4":
-                dhcp_range = tree.xpath("./ip[not(@family='ipv6')]/dhcp/range")
-            if family == "ipv6":
-                dhcp_range = tree.xpath("./ip[@family='ipv6']/dhcp/range")
-            dhcp_range[0].set("start", range_start)
-            dhcp_range[0].set("end", range_end)
-            self.wvm.networkDefineXML(etree.tostring(tree).decode())
+        """Refused while the network runs: the running network would keep the old range."""
+        if self.is_active():
+            raise util.OperationError(f"Stop network {self.net.name()} to change its DHCP range")
+        tree = etree.fromstring(self._XMLDesc(0))
+        ip = {"ipv4": "ip[not(@family='ipv6')]", "ipv6": "ip[@family='ipv6']"}.get(family)
+        dhcp_range = tree.xpath(f"{ip}/dhcp/range") if ip else []
+        if not dhcp_range:
+            raise util.OperationError(f"Network {self.net.name()} has no {family} DHCP range")
+        dhcp_range[0].set("start", range_start)
+        dhcp_range[0].set("end", range_end)
+        self.wvm.networkDefineXML(etree.tostring(tree).decode())
 
     def delete_fixed_address(self, ip, family="ipv4"):
         tree = etree.fromstring(self._XMLDesc(0))