T6928: Doc update: Support for custom interface type

docs/configuration/interfaces/index.rst

@@ -21,6 +21,7 @@ Interfaces
    pseudo-ethernet
    sstp-client
    tunnel
+   utunnel
    virtual-ethernet
    vti
    vxlan

docs/configuration/interfaces/utunnel.rst

@@ -0,0 +1,83 @@
+:lastproofread: 2024-12-12
+
+.. _custom-tunnel-interface:
+
+#############
+Custom Tunnel
+#############
+
+This article touches on custom tunnel devices.
+
+All those protocols are grouped under ``interfaces utunnel`` in VyOS. Let's take
+a closer look at the protocols and options currently supported by VyOS.
+
+Common interface configuration
+------------------------------
+
+.. cmdinclude:: /_include/interface-address.txt
+  :var0: utunnel
+  :var1: tun0
+
+.. cmdinclude:: /_include/interface-description.txt
+  :var0: utunnel
+  :var1: tun0
+
+.. cmdinclude:: /_include/interface-disable.txt
+  :var0: utunnel
+  :var1: tun0
+
+
+.. cfgcmd:: set interfaces utunnel <interface> tunnel-type <tunnel-type>
+
+This is one of the simplest types of custom tunnels, see :ref:`tunnel-type-config`
+
+An example:
+
+.. code-block:: none
+
+  set interfaces utunnel tun0 tunnel-type clash
+
+.. cfgcmd:: set interfaces utunnel <interface> manage-type <external>
+
+This option defines how interface is managed.
+
+* ``external``: Tunnel device is created/deleted by external program.
+
+An example:
+
+.. code-block:: none
+
+  set interfaces utunnel tun0 manage-type external
+
+
+.. _tunnel-type-config:
+
+Tunnel type configuration
+-------------------------
+
+Tunnel-type can be defined by yaml under ``/config/utunnels``.
+For example, with ``clash.yaml`` and ``socks5proxy.yaml``, you can do
+
+.. code-block:: none
+
+  set interfaces utunnel tun0 tunnel-type clash
+  set interfaces utunnel tun1 tunnel-type socks5proxy
+
+Example file ``/config/utunnels/clash.yaml``:
+
+.. code-block:: yaml
+
+  type: clash
+  scripts:
+    start: /usr/bin/python3 /config/clash/bin/clashctl.py start {device}
+    stop: /usr/bin/python3 /config/clash/bin/clashctl.py stop {device}
+    update: /usr/bin/python3 /config/clash/bin/clashctl.py reload {device}
+    status: systemctl status clash@{device}
+
+
+
+Example project: `vyos-clash`_
+
+
+.. _`vyos-clash`: https://github.com/sskaje/vyos-clash
+