Automatic local gateway router backup of a network gateway router is disclosed. A local gateway router communicatively coupled to a local subnet determines that a network gateway router that serves as a default gateway router for the local subnet has stopped responding. The local gateway router and the network gateway router are configured to communicate with one another via a tunnel implemented by a tunneling protocol. In response to determining that the network gateway router has stopped responding, automatically switching, by the local gateway router, from a tunneling mode to a routing mode, such that the local gateway router becomes the default gateway router for the local subnet.