.PP
The PROTO target modifies the protocol number in IP packet header.
.TP
\fB\-\-proto-set\fP \fIproto_num\fP
This option is mandatory. \fIproto_num\fP is the protocol number to which you want to
modify the packets.
.TP
\fB\-\-stop-at-frag\fP
This option is only valid for IPv6 rules. When specifying this option, the
fragment extension header will be seen as a non-extension header.
.TP
\fB\-\-stop-at-auth\fP
This option is only valid for IPv6 rules. When specifying this option, the
authentication extension header will be seen as a non-extension header.
.PP
For IPv4 packets, the \fBProtocol\fP field is modified and the checksum is
re-calculated.
.PP
For IPv6 packets, the scenario can be more complex due to the introduction of
the extension headers mechanism. By default, the PROTO target will scan the IPv6
packet, finding the last extension header and modify its \fBNext-header\fP field.
Normally, the following headers will be seen as an extension header:
\fINEXTHDR_HOP\fP,
\fINEXTHDR_ROUTING\fP,
\fINEXTHDR_FRAGMENT\fP,
\fINEXTHDR_AUTH\fP,
\fINEXTHDR_DEST\fP.
.PP
For fragmented packets, only the first fragment is processed and other fragments
are not touched.