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tcp.7: tcp_syncookies: It is now an integer [0, 2] 

Since Linux kernel 3.12, tcp_syncookies can have the value 2,
which sends out cookies unconditionally.

Related kernel commits:
5ad37d5deee1ff7150a2d0602370101de158ad86
d8513df2598e5142f8a5c4724f28411936e1dfc7

Reported-by: Philip Rowlands <linux-kernel@dimebar.com>
Signed-off-by: Alejandro Colomar <alx.manpages@gmail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Alejandro Colomar 2020-12-11 19:47:10 +01:00 committed by Michael Kerrisk
parent b5dae39596
commit 3af0cb4890
1 changed files with 13 additions and 2 deletions
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15
man7/tcp.7
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@ -830,12 +830,11 @@ The maximum number of times a SYN/ACK segment
for a passive TCP connection will be retransmitted.
This number should not be higher than 255.
.TP
.IR tcp_syncookies " (Boolean; since Linux 2.2)"
.IR tcp_syncookies " (integer; default: 1; since Linux 2.2)"
.\" Since 2.1.43
Enable TCP syncookies.
The kernel must be compiled with
.BR CONFIG_SYN_COOKIES .
Send out syncookies when the syn backlog queue of a socket overflows.
The syncookies feature attempts to protect a
socket from a SYN flood attack.
This should be used as a last resort, if at all.
@ -849,6 +848,18 @@ For recommended alternatives see
.IR tcp_synack_retries ,
and
.IR tcp_abort_on_overflow .
Set to one of the following values:
.RS
.IP 0 3
Disable TCP syncookies.
.IP 1
Send out syncookies when the syn backlog queue of a socket overflows.
.IP 2
(since Linux 3.12)
.\" commit 5ad37d5deee1ff7150a2d0602370101de158ad86
Send out syncookies unconditionally.
This can be useful for network testing.
.RE
.TP
.IR tcp_timestamps " (integer; default: 1; since Linux 2.2)"
.\" Since 2.1.36