From: Maciej Żenczykowski <maze@xxxxxxxxxx> This appears to be a common, but hard to debug, misconfiguration. Signed-off-by: Maciej Żenczykowski <maze@xxxxxxxxxx> --- extensions/libip6t_REJECT.man | 15 +++++++++++++++ extensions/libipt_REJECT.man | 15 +++++++++++++++ 2 files changed, 30 insertions(+) diff --git a/extensions/libip6t_REJECT.man b/extensions/libip6t_REJECT.man index 0030a51f..b6474811 100644 --- a/extensions/libip6t_REJECT.man +++ b/extensions/libip6t_REJECT.man @@ -30,3 +30,18 @@ TCP RST packet to be sent back. This is mainly useful for blocking hosts (which won't accept your mail otherwise). \fBtcp\-reset\fP can only be used with kernel versions 2.6.14 or later. +.PP +\fIWarning:\fP if you are using connection tracking and \fBACCEPT\fP'ing +\fBESTABLISHED\fP (and possibly \fBRELATED\fP) state packets, do not +indiscriminately \fBREJECT\fP (especially with \fITCP RST\fP) \fBINVALID\fP +state packets. Sometimes naturally occuring packet reordering will result +in packets being considered \fBINVALID\fP and the generated \fITCP RST\fP +will abort an otherwise healthy connection. +.P +Suggested use: +.br + -A INPUT -m state ESTABLISHED,RELATED -j ACCEPT +.br + -A INPUT -m state INVALID -j DROP +.br +(and -j REJECT rules go here at the end) diff --git a/extensions/libipt_REJECT.man b/extensions/libipt_REJECT.man index 8a360ce7..d0f0f19b 100644 --- a/extensions/libipt_REJECT.man +++ b/extensions/libipt_REJECT.man @@ -30,3 +30,18 @@ TCP RST packet to be sent back. This is mainly useful for blocking hosts (which won't accept your mail otherwise). .IP (*) Using icmp\-admin\-prohibited with kernels that do not support it will result in a plain DROP instead of REJECT +.PP +\fIWarning:\fP if you are using connection tracking and \fBACCEPT\fP'ing +\fBESTABLISHED\fP (and possibly \fBRELATED\fP) state packets, do not +indiscriminately \fBREJECT\fP (especially with \fITCP RST\fP) \fBINVALID\fP +state packets. Sometimes naturally occuring packet reordering will result +in packets being considered \fBINVALID\fP and the generated \fITCP RST\fP +will abort an otherwise healthy connection. +.P +Suggested use: +.br + -A INPUT -m state ESTABLISHED,RELATED -j ACCEPT +.br + -A INPUT -m state INVALID -j DROP +.br +(and -j REJECT rules go here at the end) -- 2.26.2.645.ge9eca65c58-goog
