diff --git a/de/heat-templates/top.yaml b/de/heat-templates/top.yaml
index 9127301..4f555c8 100644
--- a/de/heat-templates/top.yaml
+++ b/de/heat-templates/top.yaml
@@ -153,6 +153,13 @@
   tun_network_cidr:
     type: string
     default: '10.15.0.0/24'
+  # When tun interface is added to ovs bridge inside vm,
+  # and arp responder is enabled on undercloud,
+  # ip adresses from tun network pool can't be used for
+  # configuring vxlan tunnels through ovs bridge (https://mirantis.jira.com/browse/PRODX-9337).
+  # Ip addresses unknown for arp responder should be used.
+  # In deployment pipeline addresses assigned by openstack to advanced compute nodes
+  # are changed inside instance to 10.15.0.1XX for this case.
   tun_network_pool_start:
     type: string
     default: '10.15.0.2'