LUDOC-431 lnet: doc for asymmetrical route checking

This patch adds documentation for the asymmetrical route checking
feature, as implemented by LU-11894.
This doc is added under the Configuring LNet via lnetctl section of
the Configuring Lustre Networking chapter.

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: Ia3214528b2bd3ae3e62dc40c06ce1b3ed565e2f3
Reviewed-on: https://review.whamcloud.com/34120
Reviewed-by: Amir Shehata <ashehata@whamcloud.com>
Tested-by: Jenkins
Reviewed-by: Olaf Weber <olaf.weber@hpe.com>
Reviewed-by: Joseph Gmitter <jgmitter@whamcloud.com>

diff --git a/ConfiguringLNet.xml b/ConfiguringLNet.xml
index 80b1b81..2c450df 100755 (executable)
--- a/ConfiguringLNet.xml
+++ b/ConfiguringLNet.xml
@@ -117,7 +117,8 @@
         global:
         numa_range: 0
         max_intf: 200
-        discovery: 1</screen>
+        discovery: 1
+        drop_asym_route: 0</screen>
     </section>
     <section xml:id="lnet_config.lnetaddshowdelete">
       <title><indexterm><primary>LNet</primary>
@@ -508,6 +509,37 @@ set large_buffers: set large routing buffers
 > lnetctl set small_buffers 0
 > lnetctl set large_buffers 0</screen>
     </section>
+    <section condition='l2D' xml:id="lnet_config.asym_route">
+      <title><indexterm>
+          <primary>LNet</primary>
+          <secondary>cli</secondary>
+         <tertiary>asymmetrical route</tertiary>
+        </indexterm>Asymmetrical Routes</title>
+       <section xml:id="lnet_config.asym_route.overview">
+        <title>Overview</title>
+       <para>An asymmetrical route is when a message from a remote peer is
+         coming through a router that is not known by this node
+         to reach the remote peer.</para>
+       <para>Asymmetrical routes can be an issue when debugging network, and
+         allowing them also opens the door to attacks where hostile clients
+         inject data to the servers.</para>
+       <para>So it is possible to activate a check in LNet, that will detect
+         any asymmetrical route message and drop it.</para>
+       </section>
+       <section xml:id="lnet_config.dynamic_discovery.configuration">
+        <title>Configuration</title>
+       <para>In order to switch asymmetric route detection on or off, the
+         following command is used:</para>
+       <screen>lnetctl set drop_asym_route [0 | 1]</screen>
+       <para>This command works on a per-node basis. This means each node in a
+         Lustre cluster can decide whether it accepts asymmetrical route
+         messages.</para>
+       <para>To check the current <literal>drop_asym_route</literal> setting, the
+          <literal>lnetctl global show</literal> command can be used as shown in
+          <xref linkend="lnet_config.show_global_settings"/>.</para>
+       <para>By default, asymmetric route detection is off.</para>
+       </section>
+    </section>
     <section>
       <title><indexterm>
           <primary>LNet</primary>