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+.. _vpp_sswan_doc:
+
+VPP-SSWAN
+=======================
+
+``VPP-SSWAN`` is a StrongSwan plugin that helps offloading Strongswan IPsec ESP
+process from Linux Kernel to ``VPP``.
+
+The ``VPP-SSWAN`` takes advantage of ``StrongSwan`` extendable plugin design
+and translates ``StrongSwan`` SA creation/deletion and routing
+update operations into ``VPP`` C API calls. The successful execution of the
+API calls means the operations shall be performed by VPP smoothly.
+
+Inside ``VPP-SSWAN``, the kernel-vpp plugin is an interface to the IPsec and
+networking backend for `VPP <https://wiki.fd.io/view/VPP>`__ platform using
+the `VPP C API <https://wiki.fd.io/view/VPP/How_To_Use_The_C_API>`__.
+It provides address and routing lookup functionality and installs routes for
+IPsec traffic.
+
+The plugin also installs and maintains Security Associations and Policies to
+the `VPP IPsec <https://wiki.fd.io/view/VPP/IPSec_and_IKEv2#IPSec>`__.
+
+Since ``StrongSwan`` expects both IKE and IPsec traffic coming through the
+same network protected interfaces, the ``VPP-SSWAN`` expects the IKE traffic
+being diverted to Linux Kernel through the help of
+`VPP Linux Control Plane <https://s3-docs.fd.io/vpp/22.10/developer/plugins/
+lcp.html>`__. It is important to notice that due to LCP is a Tun/Tap interface,
+the IPsec performance will be limited by it if Transport mode of IPsec is used.
+
+Prerequisites
+-------------
+
+``VPP`` in release mode should be built before compiling ``vpp-swan plugin``.
+User may install ``StrongSwan`` prior to compile the plugin. However the
+plugin requires downloading ``StrongSwan`` source to include some of its
+header files to compile ``VPP-SSWAN``. In addition ``libsystemd-dev``
+should be installed prior to compile the plugin.
+
+Please Note: ONLY Strongswan version ``5.9.5`` and ``5.9.6`` were tested with
+this plugin.
+
+Build VPP Strongswan Plugin
+-------------
+
+``VPP-SSWAN`` requires ``StrongSwan`` source to compile. To obtain
+``StrongSwan`` the simplest way is to run the following commands:
+
+::
+
+   cd path/to/vpp/external/strongswan/vpp_swan/
+   make all
+
+Or you may download ``StrongSwan``  from its github page. It is recommended to
+use ``Strongswan`` version ``5.9.6`` or ``5.9.5`` for ``VPP-SSWAN`` to be
+compiled and integrate. The following steps are required for manually download
+``Strongswan`` source:
+
+- download strongswan source code to:
+``path/to/vpp/build/external/downloads``
+
+- unzip source code strongswan to:
+``path/to/vpp/build-root/build-vpp-native/external/sswan``
+
+- check if you have installed packages: ``libsystemd-dev`` on your OS
+
+- configure strongswan by:
+``./autogen.sh``
+``./configure --prefix=/usr --sysconfdir=/etc --enable-libipsec
+--enable-systemd --enable-swanctl --disable-gmp --enable-openssl``
+
+- compile ``vpp-swan plugin`` by:
+
+::
+
+   cd path/to/vpp/external/strongswan/vpp_swan/
+   make
+
+Build/install Strongswan (Optional)
+-------------
+
+In case you haven't installed ``Strongswan`` yet, you may use the following
+simple command to compile and install ``Strongswan`` from the downloaded source.
+
+::
+
+   cd path/to/vpp/external/strongswan/vpp_swan/
+   make pull-swan
+   make install-swan
+
+Install VPP-SWAN plugin into StrongSwan
+-------------
+
+After the ``VPP-SSWAN`` plugin has been built and ``Strongswan`` was installed,
+the following command will install the ``VPP-SSWAN`` plugin into ``Strongswan``.
+
+::
+
+   cd path/to/vpp/external/strongswan/vpp_swan/
+   make install
+
+Or you can manually copy ``libstrongswan-kernel-vpp.so`` into:
+``/usr/lib/ipsec/plugins``,
+and also ``kernel-vpp.conf`` into: ``/etc/strongswan.d/charon/``
+
+Now you can restart ``Strongswan`` by executing the following command:
+
+::
+
+   systemctl restart strongswan.service
+
+Configuration Strongswan
+-------------
+
+As an example, ``swanctl.conf`` file provides an example configuration to
+initialize connections between two endpoints.
+
+You may update the file based on your need and Copy into:
+``/etc/swanctl/conf.d/swanctl.conf``
+
+Configuration VPP
+-------------
+
+Some special treatment to VPP are required in your VPP ``startup.conf``.
+Since we use ``Strongswan`` to process IKE messages, we should disable VPP's
+IKEv2 plugin. Also as mentioned ``Linux Control Plane`` plugin is needed to
+route the traffic between VPP interface and Tun/Tap interface. To do so, simply
+adding the following commands:
+
+::
+
+   plugins {
+     plugin linux_cp_plugin.so { enable }
+     plugin ikev2_plugin.so { disable }
+    }
+
+   linux-cp {
+      lcp-sync
+   }
+
+Running VPP
+-------------
+
+Based on the provided sample ``swanctl.conf``, the following commands are
+required to be executed in ``VPP``:
+
+::
+
+   lcp create eth2 host-if eth2
+   set interface state eth2 up
+   set interface ip address eth2 192.168.0.2/24
+   set int state eth1 up
+   set int ip addr eth1 192.168.200.1/24
+
+In the commands above we assume ``eth2`` is the WAN interface to receive both
+IKE message and ESP encapsulated packets, and ``eth1`` is the LAN interface to
+receive plain packets to be encrypted. With the commands a ``Linux CP`` interface
+is created to mirror the ``eth2`` interface to Linux Kernel, and both interfaces
+were set the IP addresses followed by the ``swanctl.conf``.
+
+With the commands successfully executed and the security policy is succesfully
+agreed between two IKE daemons (one with VPP as IPsec processing engine), you may
+see the packets are encrypted/decrypted by VPP smoothly.
+
+Misc
+-------------
+This plugin is based on:
+`https://github.com/matfabia/strongswan
+<https://github.com/matfabia/strongswan>`__
+
+Author: Matus Fabian <matfabia@cisco.com>