diff --git a/doc/bird.sgml b/doc/bird.sgml
index 7277b2b9..aa8a53ec 100644
--- a/doc/bird.sgml
+++ b/doc/bird.sgml
@@ -470,7 +470,7 @@ to zero to disable it. An empty <cf><m/switch/</cf> is equivalent to <cf/on/
 	works in the direction from the routing table to the protocol.
 	Default: <cf/none/.
 
-	<tag>import keep filtered <m/bool/</tag>
+	<tag>import keep filtered <m/switch/</tag>
 	Usually, if an import filter rejects a route, the route is
 	forgotten. When this option is active, these routes are
 	kept in the routing table, but they are hidden and not
@@ -1966,6 +1966,9 @@ protocol ospf &lt;name&gt; {
 			ptp netmask &lt;switch&gt;;
 			check link &lt;switch&gt;;
 			ecmp weight &lt;num&gt;;
+			ttl security [&lt;switch&gt;; | tx only]
+			tx class|dscp &lt;num&gt;;
+			tx priority &lt;num&gt;;
 			authentication [none|simple|cryptographic];
 			password "&lt;text&gt;";
 			password "&lt;text&gt;" {
@@ -2236,6 +2239,20 @@ protocol ospf &lt;name&gt; {
 	 prefix) is propagated. It is possible that some hardware
 	 drivers or platforms do not implement this feature. Default value is no.
 
+	<tag>ttl security [<m/switch/ | tx only]</tag>
+	 TTL security is a feature that protects routing protocols
+	 from remote spoofed packets by using TTL 255 instead of TTL 1
+	 for protocol packets destined to neighbors. Because TTL is
+	 decremented when packets are forwarded, it is non-trivial to
+	 spoof packets with TTL 255 from remote locations. Note that
+	 this option would interfere with OSPF virtual links.
+
+	 If this option is enabled, the router will send OSPF packets
+	 with TTL 255 and drop received packets with TTL less than
+	 255. If this option si set to <cf/tx only/, TTL 255 is used
+	 for sent packets, but is not checked for received
+	 packets. Default value is no.
+
 	<tag>tx class|dscp|priority <m/num/</tag>
          These options specify the ToS/DiffServ/Traffic class/Priority
          of the outgoing OSPF packets. See <ref id="dsc-prio" name="tx
@@ -2784,6 +2801,26 @@ makes it pretty much obsolete. (It is still usable on very small networks.)
 	  any periodic messages to this interface and <cf/nolisten/
 	  means that RIP will send to this interface butnot listen to it.
 
+	<tag>ttl security [<m/switch/ | tx only]</tag>
+	 TTL security is a feature that protects routing protocols
+	 from remote spoofed packets by using TTL 255 instead of TTL 1
+	 for protocol packets destined to neighbors. Because TTL is
+	 decremented when packets are forwarded, it is non-trivial to
+	 spoof packets with TTL 255 from remote locations.
+
+	 If this option is enabled, the router will send RIP packets
+	 with TTL 255 and drop received packets with TTL less than
+	 255. If this option si set to <cf/tx only/, TTL 255 is used
+	 for sent packets, but is not checked for received
+	 packets. Such setting does not offer protection, but offers
+	 compatibility with neighbors regardless of whether they use
+	 ttl security.
+
+	 Note that for RIPng, TTL security is a standard behavior
+	 (required by RFC 2080), but BIRD uses <cf/tx only/ by
+	 default, for compatibility with older versions. For IPv4 RIP,
+	 default value is no.
+
 	<tag>tx class|dscp|priority <m/num/</tag>
           These options specify the ToS/DiffServ/Traffic class/Priority
           of the outgoing RIP packets. See <ref id="dsc-prio" name="tx