User manual

set network
Chapter 2 Command Descriptions 151
[TCP keepalive options]
Are options that configure how TCP keep-alive probes are sent.
The keep-alive options (“idle,” “probe_count,” “probe_interval”) should be
configured for various services that are configured by “set service
keepalive={on|off},” or clients such as autoconnect
(“set autoconnect keepalive={on|off}”).
idle=10-86400
The amount of time, in seconds, to wait while not receiving TCP
packets before sending out a keep-alive probe.
probe_count=5-30
The number of TCP keep-alive probes (specially formatted TCP
frames) to send out before closing the TCP connection.
probe_interval=10-75
The amount of time, in seconds, to wait between sending TCP keep-
alive probes.
[TCP retransmit options]
Options that control retransmission of TCP packets, including:
rto_min=30-1000 (milliseconds)
The lower bound or threshold for the TCP retransmission timeout
(RTO), in milliseconds. The default is 1000 milliseconds.
TCP uses progressively larger retransmit values, starting at a
minimum value that is calculated from a sliding window of ACK
response round-trip times that is bounded at the bottom by “rto_min.”
So, essentially, “rto_min” is not necessarily the timeout that will be
used as the starting retransmit timeout, but it is the smallest such value
that could be used.
This affects latency, because lowering “rto_min” ensures that
retransmits take place in less time if they occur. By occurring sooner,
the network is able to recover the lost data in less time at the expense
of possibly retransmitting data that is still in-flight or successfully
received by the other side, but unacknowledged due to a “delayed
ACK” mechanism or something similar. Choosing a value lower than
the default of 1000 milliseconds may help achieve improved latency
performance when retransmissions occur.
rto_max=1-240 (seconds)
The upper bound or threshold for the TCP retransmission timeout
(RTO), in seconds. When one side of a TCP connection sends a
packet and does not receive an acknowledgment from the other side
within the timeout period, the sending station retransmits the packet
and sets an exponential backoff timeout. This is done for each
successive retransmit until the maximum retransmission timeout is
reached. Then, the TCP connection resets.