diff -u -r1.3.2.6 cluster_config-macros
--- a/luci/cluster/cluster_config-macros	21 May 2009 13:32:03 -0000	1.3.2.6
+++ b/luci/cluster/cluster_config-macros	5 Aug 2010 17:59:16 -0000
@@ -621,10 +621,10 @@
 								value clusterinfo/mcast_addr |nothing" />
 					</td>
 				</tr>
+
+				<tal:block tal:condition="python:os_version == 'rhel4'">
 				<tr class="systemsTable">
-					<td class="systemsTable">
-						Multicast network interface <span tal:condition="python:os_version != 'rhel4'">(optional)</span>
-					</td>
+					<td class="systemsTable">Multicast network interface</td>
 					<td class="systemsTable">
 						<input type="text"
 							name="mcast_interface" id="mcast_interface"
@@ -633,6 +633,7 @@
 								value clusterinfo/mcast_interface |nothing" />
 					</td>
 				</tr>
+				</tal:block>
 			</tbody>
 
 			<tfoot class="systemsTable">
Index: luci/cluster/validate_config_multicast.js
===================================================================
RCS file: /cvs/cluster/conga/luci/cluster/validate_config_multicast.js,v
retrieving revision 1.3.2.4
diff -u -r1.3.2.4 validate_config_multicast.js
--- a/luci/cluster/validate_config_multicast.js	7 Feb 2008 06:52:55 -0000	1.3.2.4
+++ b/luci/cluster/validate_config_multicast.js	5 Aug 2010 17:59:16 -0000
@@ -66,7 +66,9 @@
 		clr_form_err(form.mcast[0]);
 		clr_form_err(form.mcast[1]);
 		clr_form_err(form.mcast_address);
-		clr_form_err(form.mcast_interface);
+		if (form.cluster_version && form.cluster_version.value == 'rhel4') {
+			clr_form_err(form.mcast_interface);
+		}
 	}
 
 	if (mcast == 1) {