libxt_helper.man

This module matches packets related to a specific conntrack-helper.
.TP
[\fB!\fP] \fB\-\-helper\fP \fIstring\fP
Matches packets related to the specified conntrack-helper.
.RS
.PP
string can be "ftp" for packets related to a ftp-session on default port.
For other ports append \-portnr to the value, ie. "ftp\-2121".
.PP
Same rules apply for other conntrack-helpers.
.RE