Path: utzoo!mnetor!uunet!lll-winken!lll-tis!ames!pasteur!ucbvax!LANL.GOV!cpw%sneezy
From: cpw%sneezy@LANL.GOV (C. Philip Wood)
Newsgroups: comp.protocols.tcp-ip
Subject: Re:  release of updated network sources for 4.3BSD
Message-ID: <8804071508.AA15433@sneezy>
Date: 7 Apr 88 15:08:35 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 59

For those of you with VAX's that are planning on incorporating the Berkeley
fixes, the following patch should be applied to ip_output.c.  It's the
old byte order problem coming back to haunt us...

Index:	/sys/netinet/ip_output.c 4.3 (with new inet code)
Submitted by: C. Philip Wood

Description:
	Ip_output, when called upon to fragment, sends the incorrect
	length and fragment flag in the first packet.
Repeat-By:
	Use minor internet discard protocol with udp and a packet length > the
	mtu of the network you are netting on, and monitor the network with a
	suitable tool.

		% discard -t datagram -l 1700 -p 1 doc
	
	Or, ship it through a vanilla IP gateway that keeps track of
	data length and header header length errors for IP.  Take a snap
	before and after you send the fragmented packet and watch the
	count of bad packets. 
	
		% netstat -s | grep "with data length"
		265 with data length < header length
		% netstat -s | grep "with data length"
		266 with data length < header length
	
Fix:
*** ip_output.c Wed Apr  6 11:52:50 1988
--- ip_output.c.orig    Tue Mar 15 22:12:40 1988
***************
*** 10,14 ****
   * is provided ``as is'' without express or implied warranty.
   *
!  *    @(#)ip_output.c 7.9 (LANL) 3/15/88
   */
  
--- 10,14 ----
   * is provided ``as is'' without express or implied warranty.
   *
!  *    @(#)ip_output.c 7.9 (Berkeley) 3/15/88
   */
  
***************
*** 233,238 ****
	 */
	m_adj(m0, hlen + firstlen - ip->ip_len);
!       ip->ip_len = htons((u_short)(hlen + firstlen));
!       ip->ip_off = htons((u_short)(ip->ip_off | IP_MF));
	ip->ip_sum = 0;
	ip->ip_sum = in_cksum(m0, hlen);
--- 233,238 ----
	 */
	m_adj(m0, hlen + firstlen - ip->ip_len);
!       ip->ip_len = hlen + firstlen;
!       ip->ip_off |= IP_MF;
	ip->ip_sum = 0;
	ip->ip_sum = in_cksum(m0, hlen);