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From: Jim Fleming <JimFleming@unety.net>
To: "'FreeBSD-hackers@freebsd.org'" <FreeBSD-hackers@freebsd.org>
Subject: IPv8 Tutorial #2: Minimal IPv8 Output Hack
Date: Sun, 5 May 1996 13:28:04 -0500
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IPv8 Tutorial #2: Minimal IPv8 Output Hack
---------------------------------------------------

OK...for those people that wrote asking how to generate
IPv8 packets here is a very MINIMAL hack that will allow
you to generate a few packets on your private systems.

PLEASE DO NOT TEST THIS ON THE LEGACY INTERNET
	(it has enough trouble routing IPv4)

Here is a very MINIMAL modification that can be added to:
	/usr/src/sys/netinet/ip_output.c

@@@@ ORIGINAL CODE @@@@@@@@@

(about line 280)

sendit:
        /*
         * If small enough for interface, can just send directly.
         */
        if ((u_short)ip->ip_len <= ifp->if_mtu) {
                ip->ip_len = htons((u_short)ip->ip_len);
                ip->ip_off = htons((u_short)ip->ip_off);
                ip->ip_sum = 0;
                ip->ip_sum = in_cksum(m, hlen);
                error = (*ifp->if_output)(ifp, m,
                                (struct sockaddr *)dst, ro->ro_rt);
                goto done;
        }                                      

@@@@ IPv8 TEST CODE @@@@@@@@@

sendit:
	/*
	* If small enough for interface, can just send directly.
	*/
	if ((u_short)ip->ip_len <= ifp->if_mtu) {
		ip->ip_len = htons((u_short)ip->ip_len);
		ip->ip_off = htons((u_short)ip->ip_off);
/*@*/
		/* note #1 */
		if((ip->ip_v == 4) && (ip->ip_hl == 5)){
			ip->ip_v = 8;	/* note #2 */
			ip->ip_hl = 0; 	/* note #3 */
			ip->ip_sum = 0; 	/* note #4 */
		}
		else{
			ip->ip_sum = 0;
			ip->ip_sum = in_cksum(m, hlen);
		}
/*@*/
		error = (*ifp->if_output)(ifp, m,
			(struct sockaddr *)dst, ro->ro_rt);
		goto done;
	}                                      

@@@@@@@@@@@@@@@@@@@@@@

These changes do not require the IPv8 header files or any other
variables or IPv8 routines.

Here are some notes for the above:

	1. Only small packets with simple IP headers are
		converted. With telnet and ping you can test
		some simple cases. If IPv8 traffic is carried on
		a separate network from IPv4, then it is difficult
		for crackers to be able to view all of the packets
		needed to understand a session.
	2. By rights this should be:
		ip->ip_v = 0;
		ip->ip_v |= 8;
		/* Set Galaxy Information. */
	3. The ip_hl field in IPv8 is combined with the ip_v field
		and both should be set in one operation. The
		above is only a tutorial.
	4. The ip_sum field carries the StarGate ids which are
		zero for the Legacy Internet. The statement
		ip->ip_sum = 0; could be moved before the if
		statement for only the Legacy Internet. In private
		systems security information can be placed here. The
		receiver will zap this and compute a valid checksum.
		(see IPv8 Tutorial #1: Minimal IPv8 hack)

The header file found @ <http://comm.unety.net/US/IL/Naperville/Unir>
has constant definitions and macros that can make all this more lucid.

Enjoy...
--
Jim Fleming
UNETY Systems, Inc.
Naperville, IL

e-mail: JimFleming@unety.net