Add a note on slave domains and bind-dnssec-db

diff --git a/docs/markdown/authoritative/backend-bind.md b/docs/markdown/authoritative/backend-bind.md
index 3c712ade894f3294f898d61abf72c33f9c88a932..3b662e0477bf748af44e0fcb78c5c66f8722b33b 100644 (file)
--- a/docs/markdown/authoritative/backend-bind.md
+++ b/docs/markdown/authoritative/backend-bind.md
@@ -32,6 +32,9 @@ How often to check for zone changes. See 'Operation' section.
 
 ### `bind-dnssec-db`
 Filename to store and access our DNSSEC metadatabase, empty for none.
+To slave DNSSEC-enabled domains (where the RRSIGS are in the AXFR), a
+`bind-dnssec-db` is required. This is because the [PRESIGNED](domainmetadata.md#presigned)
+domain metadata is set during the zonetransfer.
 
 ### `bind-hybrid`
 Store DNSSEC keys and metadata storage in an other backend. See the