doc: add BFD passive mode documentation

Let the user know what the new command does.

Signed-off-by: Rafael Zalamena <rzalamena@opensourcerouting.org>

diff --git a/doc/user/bfd.rst b/doc/user/bfd.rst
index 47792317ad526f256550348d4173f40f5b71fcf6..3b49a53793b07a5f390fddb1ec286a5a0712bf6a 100644 (file)
--- a/doc/user/bfd.rst
+++ b/doc/user/bfd.rst
@@ -171,6 +171,20 @@ BFD peers and profiles share the same BFD session configuration commands.
    'administrative down' message is sent to the remote peer.
 
 
+.. index:: [no] passive-mode
+.. clicmd:: [no] passive-mode
+
+   Mark session as passive: a passive session will not attempt to start
+   the connection and will wait for control packets from peer before it
+   begins replying.
+
+   This feature is useful when you have a router that acts as the
+   central node of a star network and you want to avoid sending BFD
+   control packets you don't need to.
+
+   The default is active-mode (or ``no passive-mode``).
+
+
 BFD Peer Specific Commands
 --------------------------