diff --git a/network/ports/net_vip_map_external.j2.yaml b/network/ports/net_vip_map_external.j2.yaml
index 056909e59e..0833487ce4 100644
--- a/network/ports/net_vip_map_external.j2.yaml
+++ b/network/ports/net_vip_map_external.j2.yaml
@@ -14,6 +14,12 @@ parameters:
   ControlPlaneIp:
     default: ''
     type: string
+  ControlPlaneSubnetCidr: # Here for compatibility with ctlplane_vip.yaml
+    default: ''
+    description: >
+      The subnet CIDR of the control plane network. (The parameter is
+      automatically resolved from the ctlplane subnet's cidr attribute.)
+    type: string
 {%- for network in networks if network.vip|default(false) and network.enabled|default(true) %}
   {{network.name}}Ip:
     default: ''
diff --git a/network/ports/net_vip_map_external_v6.j2.yaml b/network/ports/net_vip_map_external_v6.j2.yaml
index 935c2b845f..f28786c198 100644
--- a/network/ports/net_vip_map_external_v6.j2.yaml
+++ b/network/ports/net_vip_map_external_v6.j2.yaml
@@ -14,6 +14,12 @@ parameters:
   ControlPlaneIp:
     default: ''
     type: string
+  ControlPlaneSubnetCidr: # Here for compatibility with ctlplane_vip.yaml
+    default: ''
+    description: >
+      The subnet CIDR of the control plane network. (The parameter is
+      automatically resolved from the ctlplane subnet's cidr attribute.)
+    type: string
 {%- for network in networks if network.vip|default(false) and network.enabled|default(true) %}
   {{network.name}}Ip:
     default: ''
diff --git a/releasenotes/notes/add-ControlPlaneSubnetCidr-to-net_vip_map_external-c2c83431feaf7f35.yaml b/releasenotes/notes/add-ControlPlaneSubnetCidr-to-net_vip_map_external-c2c83431feaf7f35.yaml
new file mode 100644
index 0000000000..39e033ed89
--- /dev/null
+++ b/releasenotes/notes/add-ControlPlaneSubnetCidr-to-net_vip_map_external-c2c83431feaf7f35.yaml
@@ -0,0 +1,10 @@
+---
+fixes:
+  - |
+    The parameter ``ControlPlaneSubnetCidr`` was missing in the
+    ``network/ports/net_vip_map_external.j2.yaml`` and
+    ``network/ports/net_vip_map_external_v6.j2.yaml`` template files. This
+    caused deployment failure since the ``VipMap`` resource pass this
+    property. (See Bug: 
+    `#1864912 <https://bugs.launchpad.net/tripleo/+bug/1864912>`_)
+