How to keep it alive? What do you mean by this, which connection to keep it alive? Kindly suggest..
In regular intervals packets are sent in an existing connection to make sure the partner still is there. These packets are called "keepalive" packets. If these packets are not received the partner assumes that the other side went dead and closes the connection.
Think of a connection like a telephone call: when you talk to someone you expect some sort of acknowledgement that the other is still listening at times, be it "aha" or "hmm" or something such. If you don't get that you may ask "are you still there" - and if there is no answer you hang up. This is quite the same mechanism.
In addition to what Bakunin said:
A firewall drops or rejects a connection after a certain period if there is no activity.
A keep-alive message can be sent as a null packet periodically by the client to keep a service alive. This keeps the firewall from dropping the connection. Of course if this is done liberally by every host for every connection then the connection table in the firewall would become too long. That is why some firewalls detect this behavior and ignore keepalives messages.
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I know this is an old discussion - but your problem is, imho, self-inflicted.
michael@x071:[/home/michael]nfso -h nfs_use_reserved_ports
Specifies using nonreserved IP port number.
Range: 0 - 1
Value of 0 will use nonreserved IP port number when the NFS client communicates with the NFS server.
In the early 1980's there was this idea that port numbers less than 1024 could be "trusted" because only the super-user (aka root) could access them. This trust has been misplaced since the late 1980's as too many processes can access this so-called trusted ports. Why trust NFS (on port 2049)? It is well above 1024. Why it that number above 2049 trust-worthy and not other numbers.
In short, "trusted ports" exist in that it is still specified that a kernel privilege is needed to "open" aka request a connection from/to any other port.
If someone, even from your local security, says they MUST be 1023 and smaller - of course you can comply - BUT they are causing another security concept to become breached - availability. Not enough ports means no connectivity.
In short, port numbers - there is no added trust because a specific port number is being used. There might be a technical reason (e.g., firewall rules) to stay in a particular range - but the port number itself neither adds nor subtracts from the application security.