doc: explain rpf lookup default mode

Reported-by: Alexis Rosen <quagga-users@alexis.users.panix.com>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>

diff --git a/doc/main.texi b/doc/main.texi
index 810866aa16b66a49ca2b66e83a6d48ce6d0fac00..4c11d2440d5614187b31331e51543fe2d89e37e9 100644 (file)
--- a/doc/main.texi
+++ b/doc/main.texi
@@ -224,6 +224,11 @@ with the longer prefix length is used;  if they're equal, the
 Multicast RIB takes precedence.
 @end table
 
+The @code{mrib-then-urib} setting is the default behavior if nothing is
+configured.  If this is the desired behavior, it should be explicitly
+configured to make the configuration immune against possible changes in
+what the default behavior is.
+
 WARNING: Unreachable routes do not receive special treatment and do not
 cause fallback to a second lookup.
 @end deffn