3.1.1.9 Keepalives

As the underlying transport is based on UDP and is connectionless, each pair of endpoints MUST constantly send data to make sure that the other endpoint is present and is responding to network events. If there is no data to send, each endpoint MUST periodically acknowledge the last received datagram. Otherwise, the network address translation (NAT) en route between the peers can block the UDP connection.

If the sender does not receive any datagram from the receiver after 65 seconds, it is determined that the remote endpoint has entered the Closed state (section 3.1.5), and that the connection has been terminated.

Because the delivery of acknowledgments (section 3.1.1.4) is not guaranteed, the receiver SHOULD send one or more keepalive datagrams in implementation-specific<4> time intervals smaller or equal to 65 seconds. If the sender does not receive at least one keep-alive datagram every 65 seconds, it terminates the connection.