diff --git a/source/manual/how-tos/carp.rst b/source/manual/how-tos/carp.rst
index de3570a9..b223974a 100644
--- a/source/manual/how-tos/carp.rst
+++ b/source/manual/how-tos/carp.rst
@@ -66,6 +66,12 @@ can be found under System -> High Availability.
 Setup interfaces & basic firewall rules
 -----------------------------------------
 
+.. Warning::
+    Make sure the interface assignments on both systems are identical!
+    Via **Interfaces->Overview** you can check if e.g. DMZ is opt1 on 
+    both machines. When the assigments differ you will have mixed 
+    Master and Backup IPs on both machines.
+
 Our example uses three interfaces, which all have a rather basic setup.
 
 .. rubric:: Master