diff --git a/doc/bird.sgml b/doc/bird.sgml
index b4e5d176..e531da40 100644
--- a/doc/bird.sgml
+++ b/doc/bird.sgml
@@ -3491,6 +3491,11 @@ protocol ospf [v2|v3] <name> {
Specifies interval in seconds between retransmissions of unacknowledged
updates. Default value is 5.
+
+ Specifies estimated transmission delay of link state updates send over
+ the interface. The value is added to LSA age of LSAs propagated through
+ it. Default value is 1.
+
On every multiple access network (e.g., the Ethernet) Designated Router
and Backup Designated router are elected. These routers have some special