Skip to main content

tcp_keepalive and tcp_retries

The Proc entries to change the timeout values for TCP keep alive and TCP retransmissions.
1) TCP Keep-Alive:
A) tcp_keepalive_time:
The number of seconds a connection needs to be idle before TCP
begins sending out keep-alive probes. Keep-alives are only sent
when the SO_KEEPALIVE socket option is enabled. The default
value is 7200 seconds (2 hours).
This default value can be changed by over writing the proc entry.
example: echo 20 > /proc/sys/net/ipv4/tcp_keepalive_time.
B) tcp_keepalive_probes:
The maximum number of TCP keep-alive probes to send before giving
up and killing the connection if no response is obtained
from the other end. The default value is 9.
Corresponding proc entry to change this value.
example: echo 2 > /proc/sys/net/ipv4/tcp_keepalive_probes
C) tcp_keepalive_intvl:
The number of seconds between TCP keep-alive probes. The
default value is 75 seconds.
Corresponding proc entry to change this value.
example: echo 10 > /proc/sys/net/ipv4/tcp_keepalive_intvl

Note:
1) what ever values has taken in examples is the values that we set for USBIP server.
2) Keepalive timer will be kicked off when there is no data transaction on that particular socket.
Cases in which Heart Beat Fails:
The HeartBeat will fail to close the connection when the device has got the data to send or the board
has some response to send. For ISOCH IN devices there will be always some data to send.
2) TCP Retransmissions:
1) TCP retransmission timer will be start as soon as the data has been given to the
IP layer and this timer will be initiated if no ACK is received for this packet.
2) The maximum number of times a TCP packet is retransmitted in established state before giving up
is based on "TCP_RETRIES2" value. The default value is 15, which corresponds to a duration of approximately 13 min, depending on
the retransmission timeout.
3) The interval between two successive retransmissions will be increased exponentially.
(This is based on the RTT value).
4) we can close the connection early by reducing either "Maximum Retransmission time out" or by reducing the "number of retries".
5) we are reducing the number of retries value to "5", which will take approximately 17 seconds to close the connection.
The proc entry to change this value is
/proc/sys/net/ipv4/tcp_retries2

Comments

Popular posts from this blog

Xilinx's Interview Questions

Xilinx is the world's one of largest supplier of programmable logic devices. It has started R & D department in Hyderabad, India. It has broad scope for embedded system programming in device driver in linux.

Before the interview you have to feel the Xilinx form with information containing all academic details, current/previous employer, contacts of employer( to check out info about you), current ctc, expected ctc and expected date of joining, etc.

I appeared two back to back technical interviews.

The first interview was taken by a young man look like just crossed 30's.

He asked me to tell me about myself.

Then he asked my experience.

He checked my expertise in resume.

He asked questions about RTOS, and Linux Device Drivers.
What is RTOS ? Define it.
How a linux device driver works?
How a character driver works?

He looked at my project summaries and started to ask in depth questions about each project.

After that he asked me to write to delete nth node from starting in Singly Linked Li…

Rajasthan Board 10th Results | rajedubord.nic.in | RBSE

Raj Board of Secondary Education, Rajasthan Results at rajeduboard.nic.inBoard of Secondary Education, Rajasthan Ajmer declared result of secondary examination today at 4PM official site is rajedubord.nic.in

check Secondary Examination- 2008 Result
(To be announced on July 1st, 2008 at 4:00 PM)
source
http://rajresults.nic.in/

Declared result
Praveshika Examination-2008 Result
(Announced on June 25, 2008 at 4:00 PM)

The history of the Board of Secondary Education Rajasthan (BSER) is a remarkable panorama of progressive record of the futurological vision for developing a dynamic system of various sub-systems of examinations and highlights of the academic excellence of the last four decades. The BSER took rapid strides for promotion and development of Secondary Education in Rajasthan, spread over 3,42,239 sq. km. and in more than 6000 schools located in 32 districts involving 8.5 lakhs students for Secondary and Senior Secondary Examination in the year 2000.

At present the Board is conducting …

Delete Last Char in String C program Simple Way

How to delete the last character in a string?
Lets say I have a string "/data/share/" I want to delete the last character from the string ie "/" so that output will be "/data/share"; Here are some methods to do this in C language.
one way could be use of strncat() function;
char*strncat(char*restricts1, constchar*restricts2, size_tn);
The strncat() function appends not more than n characters from s2, and
then adds a terminating `\0'.
#include
Another simple way is,
say the string variable is str_p
Then simply put
str_p[(strlen(str_p)-1)] = '\0';
And you are done;