Increased default timeout to 300 seconds (5 minutes) per RFC 5482, which relates to the TCP_USER_TIMEOUT option. This is not the same thing since TCP_USER_TIMEOUT is effectively a timeout tied to not receiving any ACKs after a packet is sent, but I would argue that it applies here because it is the same idea: the connection is being forcibly closed after a period of inactivity or unreachability. [https://tools.ietf.org/html/rfc5482]