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tcp: Increase timeout for SYN segments 

Commit 9ad7c049 ("tcp: RFC2988bis + taking RTT sample from 3WHS for
the passive open side") changed the initRTO from 3secs to 1sec in
accordance to RFC6298 (former RFC2988bis). This reduced the time till
the last SYN retransmission packet gets sent from 93secs to 31secs.

RFC1122 is stating that the retransmission should be done for at least 3
minutes, but this seems to be quite high.

  "However, the values of R1 and R2 may be different for SYN
  and data segments.  In particular, R2 for a SYN segment MUST
  be set large enough to provide retransmission of the segment
  for at least 3 minutes.  The application can close the
  connection (i.e., give up on the open attempt) sooner, of
  course."

This patch increases the value of TCP_SYN_RETRIES to the value of 6,
providing a retransmission window of 63secs.

The comments for SYN and SYNACK retries have also been updated to
describe the current settings. The same goes for the documentation file
"Documentation/networking/ip-sysctl.txt".

Signed-off-by: Alexander Bergmann <alex@linlab.net>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alex Bergmann 2012-08-31 02:48:31 +00:00 committed by David S. Miller
parent c32f38619a
commit 6c9ff979d1
2 changed files with 20 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

8
Documentation/networking/ip-sysctl.txt
View File

@ -439,7 +439,9 @@ tcp_stdurg - BOOLEAN
tcp_synack_retries - INTEGER tcp_synack_retries - INTEGER
Number of times SYNACKs for a passive TCP connection attempt will Number of times SYNACKs for a passive TCP connection attempt will
be retransmitted. Should not be higher than 255. Default value be retransmitted. Should not be higher than 255. Default value
is 5, which corresponds to ~180seconds. is 5, which corresponds to 31seconds till the last retransmission
with the current initial RTO of 1second. With this the final timeout
for a passive TCP connection will happen after 63seconds.
tcp_syncookies - BOOLEAN tcp_syncookies - BOOLEAN
Only valid when the kernel was compiled with CONFIG_SYNCOOKIES Only valid when the kernel was compiled with CONFIG_SYNCOOKIES
@ -478,7 +480,9 @@ tcp_fastopen - INTEGER
tcp_syn_retries - INTEGER tcp_syn_retries - INTEGER
Number of times initial SYNs for an active TCP connection attempt Number of times initial SYNs for an active TCP connection attempt
will be retransmitted. Should not be higher than 255. Default value will be retransmitted. Should not be higher than 255. Default value
is 5, which corresponds to ~180seconds. is 6, which corresponds to 63seconds till the last restransmission
with the current initial RTO of 1second. With this the final timeout
for an active TCP connection attempt will happen after 127seconds.
tcp_timestamps - BOOLEAN tcp_timestamps - BOOLEAN
Enable timestamps as defined in RFC1323. Enable timestamps as defined in RFC1323.

18
include/net/tcp.h
View File

@ -98,11 +98,21 @@ extern void tcp_time_wait(struct sock *sk, int state, int timeo);
* 15 is ~13-30min depending on RTO. * 15 is ~13-30min depending on RTO.
*/ */
#define TCP_SYN_RETRIES 5 /* number of times to retry active opening a #define TCP_SYN_RETRIES 6 /* This is how many retries are done
* connection: ~180sec is RFC minimum */ * when active opening a connection.
* RFC1122 says the minimum retry MUST
* be at least 180secs. Nevertheless
* this value is corresponding to
* 63secs of retransmission with the
* current initial RTO.
*/
#define TCP_SYNACK_RETRIES 5 /* number of times to retry passive opening a #define TCP_SYNACK_RETRIES 5 /* This is how may retries are done
* connection: ~180sec is RFC minimum */ * when passive opening a connection.
* This is corresponding to 31secs of
* retransmission with the current
* initial RTO.
*/
#define TCP_TIMEWAIT_LEN (60*HZ) /* how long to wait to destroy TIME-WAIT #define TCP_TIMEWAIT_LEN (60*HZ) /* how long to wait to destroy TIME-WAIT
* state, about 60 seconds */ * state, about 60 seconds */