From owner-freebsd-questions  Mon Aug  5 11:20:51 2002
Delivered-To: freebsd-questions@freebsd.org
Received: from mx1.FreeBSD.org (mx1.FreeBSD.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP id 8F0CB37B400
	for <freebsd-questions@FreeBSD.ORG>; Mon,  5 Aug 2002 11:20:48 -0700 (PDT)
Received: from hotmail.com (f170.law9.hotmail.com [64.4.9.170])
	by mx1.FreeBSD.org (Postfix) with ESMTP id 49F8A43E81
	for <freebsd-questions@FreeBSD.ORG>; Mon,  5 Aug 2002 11:20:48 -0700 (PDT)
	(envelope-from soheil_h_y@hotmail.com)
Received: from mail pickup service by hotmail.com with Microsoft SMTPSVC;
	 Mon, 5 Aug 2002 11:20:48 -0700
Received: from 80.75.14.195 by lw9fd.law9.hotmail.msn.com with HTTP;
	Mon, 05 Aug 2002 18:20:47 GMT
X-Originating-IP: [80.75.14.195]
From: "soheil h" <soheil_h_y@hotmail.com>
To: freebsd-questions@FreeBSD.ORG
Cc: hassas@ce.sharif.ac.ir
Subject: accessing tcp header in the ip_input.c::ip_forward()   !!!!!
Date: Mon, 05 Aug 2002 22:50:47 +0430
Mime-Version: 1.0
Content-Type: text/plain; format=flowed
Message-ID: <F170mpN7JvVAabAQJ6j0000c5ab@hotmail.com>
X-OriginalArrivalTime: 05 Aug 2002 18:20:48.0267 (UTC) FILETIME=[D2743DB0:01C23CAC]
Sender: owner-freebsd-questions@FreeBSD.ORG
Precedence: bulk
List-ID: <freebsd-questions.FreeBSD.ORG>
List-Archive: <http://docs.freebsd.org/mail/> (Web Archive)
List-Help: <mailto:majordomo@FreeBSD.ORG?subject=help> (List Instructions)
List-Subscribe: <mailto:majordomo@FreeBSD.ORG?subject=subscribe%20freebsd-questions>
List-Unsubscribe: <mailto:majordomo@FreeBSD.ORG?subject=unsubscribe%20freebsd-questions>
X-Loop: FreeBSD.ORG

hi list
i made a change in ip_forward() in ip_input.c  to print the window sizes 
passes through my gateway.
but it doesn't work properly and doesn't show the true th_win (window size) 
and the th_dport they doesn't mach the tcpdump output
but shows the true ip->ip_p for TCP
it means that i make a wrong cast in ip packet means not at the place of the 
tcphdr some byte more or less i don't know
please verify me if my code is true and if not please help me !!!!!

i make a struct named tcpShdr in tcpS.h file(my file ;) ):

(the tcphdr with a litte change on field definition)
struct tcpShdr {
	u_short	th_sport;		/* source port */
	u_short	th_dport;		/* destination port */
	tcpS_seq th_seq;			/* sequence number */
	tcpS_seq	th_ack;			/* acknowledgement number */
	u_short th_soheil;/* the flags and ... fields that i don't care */
	u_short	th_win;			/* window */
	u_short	th_sum;			/* checksum */
	u_short	th_urp;			/* urgent pointer */
};
in ip_input.c
...
#include <netinet/tcpS.h>
...
static void
ip_forward(m, srcrt)
	struct mbuf *m;
	int srcrt;
{
	register struct ip *ip = mtod(m, struct ip *);
	register struct sockaddr_in *sin;
	register struct rtentry *rt;
	int error, type = 0, code = 0;
	struct mbuf *mcopy;
	n_long dest;
	/*caddr_t s_c;/* pointer to tcp first bye */ */
	int s_len;/*the ip length*/
	struct tcpShdr * s_hdr; /* the header of my tcp/ip packet*/
	struct ifnet *destifp;
#ifdef IPSEC
	struct ifnet dummyifp;
#endif

	dest = 0;
#ifdef DIAGNOSTIC
	if (ipprintfs)
		printf("forward: src %lx dst %lx ttl %x\n",
		    (u_long)ip->ip_src.s_addr,
                    (u_long)ip->ip_dst.s_addr,
		    ip->ip_ttl);
#endif

	s_len = IP_VHL_HL(ip->ip_vhl) << 2;
	if(ip->ip_p == IPPROTO_TCP)
	{
		s_hdr = (struct tcpShdr *)( (caddr_t) ip +  s_len);
		if( (s_hdr->th_win) >= 4096 &&
                   (s_hdr->th_win) <= 16000 ){
			printf("win %d prot %d port %d" ,
                              s_hdr->th_win,
                              ip->ip_p,
                              s_hdr->th_dport);
		}
	}
.../* it continues on noramlly */
}

_________________________________________________________________
MSN Photos is the easiest way to share and print your photos: 
http://photos.msn.com/support/worldwide.aspx


To Unsubscribe: send mail to majordomo@FreeBSD.org
with "unsubscribe freebsd-questions" in the body of the message