Hi Alex, On 12/7/20 6:08 PM, Alejandro Colomar wrote: > 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@xxxxxxxxxxx> > Signed-off-by: Alejandro Colomar <alx.manpages@xxxxxxxxx> > Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx> > Cc: Hannes Frederic Sowa <hannes@xxxxxxxxxxxxxxxxxxx> > Cc: David S. Miller <davem@xxxxxxxxxxxxx> > --- > man7/tcp.7 | 14 ++++++++++++-- > 1 file changed, 12 insertions(+), 2 deletions(-) > > diff --git a/man7/tcp.7 b/man7/tcp.7 > index d983a8f9a..591f73d8d 100644 > --- a/man7/tcp.7 > +++ b/man7/tcp.7 > @@ -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 +848,17 @@ 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 I think it's helpful to let the reader know that this is a more recent feature. So, better: .IP 2 (since Linux 3.12) Thanks, Michael > +.\" 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 > -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/
