man: DNAT: Describe shifted port range feature

This wasn't mentioned anywhere.

Signed-off-by: Phil Sutter <phil@nwl.cc>

diff --git a/extensions/libxt_DNAT.man b/extensions/libxt_DNAT.man
index c3daea9a40394cf1739a3a3238929068301e0f9b..e044c8216fc09ed723e419e99bf0de9d7cdca105 100644 (file)
--- a/extensions/libxt_DNAT.man
+++ b/extensions/libxt_DNAT.man
@@ -10,7 +10,7 @@ should be modified (and all future packets in this connection will
 also be mangled), and rules should cease being examined.  It takes the
 following options:
 .TP
-\fB\-\-to\-destination\fP [\fIipaddr\fP[\fB\-\fP\fIipaddr\fP]][\fB:\fP\fIport\fP[\fB\-\fP\fIport\fP]]
+\fB\-\-to\-destination\fP [\fIipaddr\fP[\fB\-\fP\fIipaddr\fP]][\fB:\fP\fIport\fP[\fB\-\fP\fIport\fP[\fB/\fIbaseport\fP]]]
 which can specify a single new destination IP address, an inclusive
 range of IP addresses. Optionally a port range,
 if the rule also specifies one of the following protocols:
@@ -18,6 +18,9 @@ if the rule also specifies one of the following protocols:
 If no port range is specified, then the destination port will never be
 modified. If no IP address is specified then only the destination port
 will be modified.
+If \fBbaseport\fP is given, the difference of the original destination port and
+its value is used as offset into the mapping port range. This allows to create
+shifted portmap ranges and is available since kernel version 4.18.
 .TP
 \fB\-\-random\fP
 If option