T1457: add igmp proxy

docs/routing/igmp-proxy.rst

@@ -0,0 +1,26 @@
+.. _igmp_proxy:
+
+IGMP Proxy
+==========
+
+Internet Group Management Protocol (IGMP)
+
+A IGMP Proxy to send IGMP host messages on behalf of a connected client.
+The configuration must define one upstream interface, and one or more downstream interfaces.
+If multicast traffic originates outside the upstream subnet, the "alt-subnet" option can be used in order to define legal multicast sources.
+
+simple example:
+---------------
+
+Interface eth1 LAN is behind NAT. In order to subscribe 10.0.0.0/23 subnet multicast which is in eth0 WAN we need igmp-proxy.
+
+.. code-block:: sh
+
+  # show protocols igmp-proxy 
+  interface eth0 {
+      alt-subnet 10.0.0.0/23
+      role upstream
+  }
+  interface eth1 {
+      role downstream
+  }

docs/routing/index.rst

@@ -19,3 +19,4 @@ BGP).
    static
    mss-clamp
    routing-policy
+   igmp-proxy