TCP Keepalive是确定断开链接的唯一机制吗？

I recently ran into a issue where intermediate link betweeen a TCP server and client was down. The client has the requirement of connecting to a secondary server if the primary server is down. When the primary server is bought down (Ex ..by doing ^C on the terminal), there is TCP shutdown sequence that gets through and client sucessfully detects the broken link and tries the secondary. However if the intermediate link goes down ,the client and server would be unaware of it. The only way the client can detect is when its TCP bufferes gets filled up with failed 'send' operations.I recently ran into a issue where intermediate