HP-UX TCP/IP Performance White Paper, March 2008

tcp_keepalive_interval:

Interval for sending keep-alive probes.

If any activity has occurred on the connection or if there is any

unacknowledged data when the time-out period expires, the timer is

simply restarted. If the remote system has crashed and rebooted,

it will presumably know nothing about this connection, and it will

issue an RST in response to the ACK. Receipt of the RST will

terminate the connection.

If the keepalive packet is not ACK'd by the remote TCP, the normal

retransmission time-out will eventually exceed threshold R2, and

the connection will be terminated.

With this keepalive behavior, a connection can time-out and

terminate without actually receiving an RST from the remote TCP.

[10000, 10*24*3600000] Default: 2 * 3600000 (2 hours)

These keepalives for an established connection will only be enabled if the application uses a

setsockopt()/t_optmgt() call to enable keepalives (SO_KEEPALIVE). It is not enabled otherwise.

This differs from the behavior of tcp_keepalive_detached_interval. A large number of idle

connections, with keepalives enabled, could generate more keepalive traffic than real traffic. They could

also keep on-demand/dial-up links open unnecessarily.

tcp_largest_anon_port:

Largest anonymous port number to use. [1024, 65535]

Default: 65535

It is unlikely that this will ever need to be changed. The only reason would be to provide some similarity to

anonymous (aka ephemeral) port number assignments of older BSDish stacks. There are no checks made to

ensure that tcp_largest_anon_port is set to a sane value wrt to the smallest anonymous port number.

Setting tcp_largest_anon_port to a value smaller than tcp_smallest_anon_port will lead to

undefined behavior.

tcp_recv_hiwater_def:

The maximum size for the receive window. [4096,-]

Default: 32768 bytes

This can also be thought-of as the default receive socket buffer (aka SO_RCVBUF) size. It is used for any

connection using an interface that is NOT marked as either a "long, fat pipe" (LFP) or a "long, narrow

pipe" (LNP).

One of the "limits" to the performance of a TCP connection is based on the relationship between the TCP

window (W) and the round-trip-time (RTT) of the connection. Basically, a sending TCP cannot send more

than one window's worth of data before it must stop and wait for a "window update" from the remote. The

soonest a window update can arrive is one RTT. From this we have the function:

Throughput <= W/RTT