doc: mention requirement of additional packages for ipset
References: https://bugzilla.novell.com/561177
Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
diff --git a/extensions/libipt_set.man b/extensions/libipt_set.man
index 93b42d3..aca1bfc 100644
--- a/extensions/libipt_set.man
+++ b/extensions/libipt_set.man
@@ -17,3 +17,7 @@
.PP
The option \fB\-\-match\-set\fR can be replaced by \fB\-\-set\fR if that does
not clash with an option of other extensions.
+.PP
+Use of -m set requires that ipset kernel support is provided. As standard
+kernels do not ship this currently, the ipset or Xtables-addons package needs
+to be installed.