diff --git a/source/adminguide/autoscale_with_virtual_router.rst b/source/adminguide/autoscale_with_virtual_router.rst
index 4370fec387..a529860cdc 100644
--- a/source/adminguide/autoscale_with_virtual_router.rst
+++ b/source/adminguide/autoscale_with_virtual_router.rst
@@ -176,6 +176,20 @@ Specify the following:
    <virtual_machines.html#user-data-and-metadata>`_.
 
 
+.. note::
+   Hostnames for instances in an AutoScale Instance Group are automatically
+   generated from the group name and sanitized to meet the OS hostname rules
+   of the template. If the generated name exceeds the allowed limit,
+   it will be trimmed to fit within the limit. The limits are:
+
+   - **Windows templates:** 15 characters (NetBIOS limit).
+   - **Other OS templates:** 63 characters.
+
+   Unsupported characters may be normalized (for example, lower-cased or
+   replaced) to comply with OS constraints.
+
+
+
 AutoScale Policies
 -------------------------------------------------