add a trouble shooting section, small start.

source/index.rst

@@ -32,6 +32,7 @@ Table of Contents
      services
      plugins
      third_party_plugins
+     troubleshooting
      develop
      relations
      legal

source/troubleshooting.rst

@@ -0,0 +1,22 @@
+====================================
+Troubleshooting
+====================================
+
+.. image:: /troubleshooting/images/ask-blackboard-356079.jpg
+
+
+Sometimes, even with all the hard work done to prepare your setup, issues occur.
+Generally it's always good to check your logs (:menuselection:`System --> Log Files` or the ones found in the module your trying to setup),
+but sometimes more help is needed.
+
+
+Within this chapter we collect some of the common mistakes we have seen over the years, combined with pointers
+where to look for solutions.
+
+.. toctree::
+   :maxdepth: 2
+   :titlesonly:
+   :glob:
+
+   troubleshooting/boot
+   troubleshooting/gateways

source/troubleshooting/boot.rst

@@ -0,0 +1,30 @@
+====================================
+Boot
+====================================
+
+-----------------------------
+hangs at "booting..."
+-----------------------------
+
+On some serial connected devices the console settings are different, in which case you would
+not be able to start the installer.
+
+If you can reach the loader prompt, you could try to change some kernel parameters before booting.
+
+
+
+::
+
+    set hint.uart.0.flags=0x0
+    set hint.uart.1.flags=0x10
+    set comconsole_speed=115200
+    set comconsole_port=0x2F8
+    set console=comconsole
+    boot
+
+.. Note::
+
+    To enter the loader prompt press :code:`3` when the OPNsense boot menu is visible
+
+
+After installation, you could persist these settings in :menuselection:`System --> Settings --> Tunables`

source/troubleshooting/gateways.rst

@@ -0,0 +1,43 @@
+====================================
+Gateways and monitoring
+====================================
+
+The address you are trying to monitor should be reachable using the interface the gateway is attached to, either
+directly or using a static route (check :menuselection:`System --> Routes --> Status`).
+
+---------------------------------
+dpinger:.. sendto error: XXX
+---------------------------------
+
+Usually found in :menuselection:`System --> Log Files --> General`, every code has a meaning, usually explained in
+`errno.h <https://github.com/opnsense/src/blob/master/sys/sys/errno.h>`__ (:code:`man errno`)
+
+Some common ones are explained below:
+
+======  ==================== =================================================================================
+XX      Name                 Description
+======  ==================== =================================================================================
+55      ENOBUFS              No buffer space available. An operation on a socket or pipe was not performed
+                             because the system lacked sufficient buffer space or because a queue was full.
+                             **Check connectivity from the machine itself using** :code:`ping`, most common
+                             mistakes are misconfigured routes, interface issues (disconnected) and
+                             policy based routing issues forcing traffic to the wrong target
+                             (using :code:`reply-to`)
+64      EHOSTDOWN            Host is down. A socket operation failed because the destination host was down.
+                             **Expecting an (layer 2) ARP response but none was returned, often misconfigured
+                             subnets or hosts are actually not accessible over L2**
+65      EHOSTUNREACH         No route to host. A socket operation was attempted to an unreachable host
+                             **The routing table is a good place to look**
+                             (:menuselection:`System --> Routes --> Status`)
+======  ==================== =================================================================================
+
+------------------------------------------
+arpresolve: can't allocate llinfo for..
+------------------------------------------
+
+This message usually means that the configured gateway lies outside the configured subnets for this firewall (for IPv4).
+
+.. Tip::
+
+    Double check the subnets of your interface and virtual IP's, you can also use :menuselection:`Interfaces --> Overview`
+    for a quick list of all configured addresses.