sdn: add section about underlying technology and configuration files

document some basics of the inner workings, can definitively get
extended (and might be then better of placed somewhere else).

This makes also a bit more sense then the non-telling 'SDN' heading
left over the recent rework.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

diff --git a/pvesdn.adoc b/pvesdn.adoc
index 34e247646fe03fb9717e0fb41f9e47448f8941b5..911c89f7c2aeca5bff90cb4807ab982c478b2aa1 100644 (file)
--- a/pvesdn.adoc
+++ b/pvesdn.adoc
@@ -64,10 +64,8 @@ assigned to VMs and Containers.
 Main Configuration
 ~~~~~~~~~~~~~~~~~~
 
-Configuration is done at the web UI at datacenter level and is saved in files
-located in the shared configuration file system at `/etc/pve/sdn`.
-
-On the web interface, SDN features the following sections:
+Configuration is done at the web UI at datacenter level, separated into the
+following sections:
 
 * SDN:: Here you get an overview of the current active SDN state, and you can
   apply all pending changes to the whole cluster.
@@ -91,15 +89,31 @@ in your SDN setup.
   virtual guests' hostname and IP
   addresses
 
-[[pvesdn_config_main_sdn]]
-SDN
-~~~
+[[pvesdn_tech_and_config_overview]]
+Technology & Configuration
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The {pve} Software-Defined Network implementation uses standard Linux networking
+as much as possible. The reason for this is that modern Linux networking
+provides almost all needs for a feature full SDN implementation and avoids adding
+external dependencies and reduces the overall amount of components that can
+break.
+
+The {pve} SDN configurations are located in `/etc/pve/sdn`, which is shared with
+all other cluster nodes through the {pve} xref:chapter_pmxcfs[configuration file system].
+Those configurations get translated to the respective configuration formats of
+the tools that manage the underlying network stack (for example `ifupdown2` or
+`frr`).
+
+New changes are not immediately applied but recorded as pending first. You can
+then apply a set of different changes all at once in the main 'SDN' overview
+panel on the web interface. This system allows to roll-out various changes as
+single atomic one.
 
-This is the main status panel. Here you can see the deployment status of zones
-on different nodes.
+The SDN tracks the rolled-out state through the '.running-config' and '.version'
+files located in '/etc/pve/sdn'.
 
-Pressing the 'Apply' button reloads the local configuration on all cluster
-nodes.
+// TODO: extend implementation and technology details.
 
 [[pvesdn_config_zone]]
 Zones