text: /*
   * Copyright (c) 1982, 1986 Regents of the University of California.
   * All rights reserved.
   *
   * Redistribution and use in source and binary forms are permitted
   * provided that this notice is preserved and that due credit is given
   * to the University of California at Berkeley. The name of the University
   * may not be used to endorse or promote products derived from this
   * software without specific prior written permission. This software
   * is provided ``as is'' without express or implied warranty.
   *
   *	@(#)ip_input.c	7.9.2 (2.11BSD GTE) 1995/10/09
   */
  
  #include <sys/param.h>
  #include <sys/systm.h>
  #include <sys/mbuf.h>
  #include <sys/domain.h>
  #include <sys/protosw.h>
  #include <sys/socket.h>
  #include <sys/errno.h>
  #include <sys/time.h>
  #include <sys/kernel.h>
  
  #include <net/route.h>
  #include <net/if.h>
  
  #include <netinet/in.h>
  #include <netinet/in_pcb.h>
  #include <netinet/in.h>
  #include <netinet/in_systm.h>
  #include <netinet/ip.h>
  #include <netinet/ip_var.h>
  #include <netinet/ip_icmp.h>
  #include <netinet/tcp.h>
  
  extern	int	ipforwarding, ipsendredirects, ipforward_srcrt, ip_defttl;
  u_char	ip_protox[IPPROTO_MAX];
  int	ipqmaxlen = IFQ_MAXLEN;
  int	ipprintfs = 0;
  struct	in_ifaddr *in_ifaddr;			/* first inet address */
  
  /*
   * We need to save the IP options in case a protocol wants to respond
   * to an incoming packet over the same route if the packet got here
   * using IP source routing.  This allows connection establishment and
   * maintenance when the remote end is on a network that is not known
   * to us.
   */
  int	ip_nhops = 0;
  static	struct ip_srcrt {
  	char	nop;				/* one NOP to align */
  	char	srcopt[IPOPT_OFFSET + 1];	/* OPTVAL, OLEN and OFFSET */
  	struct	in_addr route[MAX_IPOPTLEN];
  } ip_srcrt;
  
  /*
   * IP initialization: fill in IP protocol switch table.
   * All protocols not implemented in kernel go to raw IP protocol handler.
   */
  ip_init()
  {
  	register struct protosw *pr;
  	register int i;
  extern	struct	timeval time;
  	struct	timeval	nettime;
  
  	pr = pffindproto(PF_INET, IPPROTO_RAW, SOCK_RAW);
  	if (pr == 0)
  		panic("ip_init");
  	for (i = 0; i < IPPROTO_MAX; i++)
  		ip_protox[i] = pr - inetsw;
  	for (pr = inetdomain.dom_protosw;
  	    pr < inetdomain.dom_protoswNPROTOSW; pr++)
  		if (pr->pr_domain->dom_family == PF_INET &&
  		    pr->pr_protocol && pr->pr_protocol != IPPROTO_RAW)
  			ip_protox[pr->pr_protocol] = pr - inetsw;
  	ipq.next = ipq.prev = &ipq;
  	cpfromkern(&time, &nettime, sizeof (struct timeval));
  	ip_id = nettime.tv_sec & 0xffffL;
  	ipintrq.ifq_maxlen = ipqmaxlen;
  }
  
  u_char	ipcksum = 1;
  struct	ip *ip_reass();
  struct	sockaddr_in ipaddr = { AF_INET };
  struct	route ipforward_rt;
  
  /*
   * Ip input routine.  Checksum and byte swap header.  If fragmented
   * try to reassamble.  If complete and fragment queue exists, discard.
   * Process options.  Pass to next level.
   */
  ipintr()
  {
  	register struct ip *ip;
  	register struct mbuf *m;
  	struct mbuf *m0;
  	register int i;
  	register struct ipq *fp;
  	register struct in_ifaddr *ia;
  	struct ifnet *ifp;
  	int hlen, s;
  
  next:
  	/*
  	 * Get next datagram off input queue and get IP header
  	 * in first mbuf.
  	 */
  	s = splimp();
  	IF_DEQUEUEIF(&ipintrq, m, ifp);
  	splx(s);
  	if (m == 0)
  		return;
  	/*
  	 * If no IP addresses have been set yet but the interfaces
  	 * are receiving, can't do anything with incoming packets yet.
  	 */
  	if (in_ifaddr == NULL)
  		goto bad;
  	ipstat.ips_total++;
  	if ((m->m_off > MMAXOFF || m->m_len < sizeof (struct ip)) &&
  	    (m = m_pullup(m, sizeof (struct ip))) == 0) {
  		ipstat.ips_toosmall++;
  		goto next;
  	}
  	ip = mtod(m, struct ip *);
  	hlen = ip->ip_hl << 2;
  	if (hlen < sizeof(struct ip)) {	/* minimum header length */
  		ipstat.ips_badhlen++;
  		goto bad;
  	}
  	if (hlen > m->m_len) {
  		if ((m = m_pullup(m, hlen)) == 0) {
  			ipstat.ips_badhlen++;
  			goto next;
  		}
  		ip = mtod(m, struct ip *);
  	}
  	if (ipcksum)
  		if (ip->ip_sum = in_cksum(m, hlen)) {
  			ipstat.ips_badsum++;
  			goto bad;
  		}
  
  	/*
  	 * Convert fields to host representation.
  	 */
  	ip->ip_len = ntohs((u_short)ip->ip_len);
  	if (ip->ip_len < hlen) {
  		ipstat.ips_badlen++;
  		goto bad;
  	}
  	ip->ip_id = ntohs(ip->ip_id);
  	ip->ip_off = ntohs((u_short)ip->ip_off);
  
  	/*
  	 * Check that the amount of data in the buffers
  	 * is as at least much as the IP header would have us expect.
  	 * Trim mbufs if longer than we expect.
  	 * Drop packet if shorter than we expect.
  	 */
  	i = -(u_short)ip->ip_len;
  	m0 = m;
  	for (;;) {
  		i += m->m_len;
  		if (m->m_next == 0)
  			break;
  		m = m->m_next;
  	}
  	if (i != 0) {
  		if (i < 0) {
  			ipstat.ips_tooshort++;
  			m = m0;
  			goto bad;
  		}
  		if (i <= m->m_len)
  			m->m_len -= i;
  		else
  			m_adj(m0, -i);
  	}
  	m = m0;
  
  	/*
  	 * Process options and, if not destined for us,
  	 * ship it on.  ip_dooptions returns 1 when an
  	 * error was detected (causing an icmp message
  	 * to be sent and the original packet to be freed).
  	 */
  	ip_nhops = 0;		/* for source routed packets */
  	if (hlen > sizeof (struct ip) && ip_dooptions(ip, ifp))
  		goto next;
  
  	/*
  	 * Check our list of addresses, to see if the packet is for us.
  	 */
  	for (ia = in_ifaddr; ia; ia = ia->ia_next) {
  #define	satosin(sa)	((struct sockaddr_in *)(sa))
  
  		if (IA_SIN(ia)->sin_addr.s_addr == ip->ip_dst.s_addr)
  			goto ours;
  		if (
  #ifdef	DIRECTED_BROADCAST
  		    ia->ia_ifp == ifp &&
  #endif
  		    (ia->ia_ifp->if_flags & IFF_BROADCAST)) {
  			u_long t;
  
  			if (satosin(&ia->ia_broadaddr)->sin_addr.s_addr ==
  			    ip->ip_dst.s_addr)
  				goto ours;
  			if (ip->ip_dst.s_addr == ia->ia_netbroadcast.s_addr)
  				goto ours;
  			/*
  			 * Look for all-0's host part (old broadcast addr),
  			 * either for subnet or net.
  			 */
  			t = ntohl(ip->ip_dst.s_addr);
  			if (t == ia->ia_subnet)
  				goto ours;
  			if (t == ia->ia_net)
  				goto ours;
  		}
  	}
  	if (ip->ip_dst.s_addr == (u_long)INADDR_BROADCAST)
  		goto ours;
  	if (ip->ip_dst.s_addr == INADDR_ANY)
  		goto ours;
  
  	/*
  	 * Not for us; forward if possible and desirable.
  	 */
  	if (ipforwarding == 0) {
  		ipstat.ips_cantforward++;
  		m_freem(m);
  	} else
  		ip_forward(ip, ifp, 0);
  	goto next;
  
  ours:
  	/*
  	 * If offset or IP_MF are set, must reassemble.
  	 * Otherwise, nothing need be done.
  	 * (We could look in the reassembly queue to see
  	 * if the packet was previously fragmented,
  	 * but it's not worth the time; just let them time out.)
  	 */
  	if (ip->ip_off &~ IP_DF) {
  		/*
  		 * Look for queue of fragments
  		 * of this datagram.
  		 */
  		for (fp = ipq.next; fp != &ipq; fp = fp->next)
  			if (ip->ip_id == fp->ipq_id &&
  			    ip->ip_src.s_addr == fp->ipq_src.s_addr &&
  			    ip->ip_dst.s_addr == fp->ipq_dst.s_addr &&
  			    ip->ip_p == fp->ipq_p)
  				goto found;
  		fp = 0;
  found:
  
  		/*
  		 * Adjust ip_len to not reflect header,
  		 * set ip_mff if more fragments are expected,
  		 * convert offset of this to bytes.
  		 */
  		ip->ip_len -= hlen;
  		((struct ipasfrag *)ip)->ipf_mff = 0;
  		if (ip->ip_off & IP_MF)
  			((struct ipasfrag *)ip)->ipf_mff = 1;
  		ip->ip_off <<= 3;
  
  		/*
  		 * If datagram marked as having more fragments
  		 * or if this is not the first fragment,
  		 * attempt reassembly; if it succeeds, proceed.
  		 */
  		if (((struct ipasfrag *)ip)->ipf_mff || ip->ip_off) {
  			ipstat.ips_fragments++;
  			ip = ip_reass((struct ipasfrag *)ip, fp);
  			if (ip == 0)
  				goto next;
  			m = dtom(ip);
  		} else
  			if (fp)
  				ip_freef(fp);
  	} else
  		ip->ip_len -= hlen;
  
  	/*
  	 * Switch out to protocol's input routine.
  	 */
  	(*inetsw[ip_protox[ip->ip_p]].pr_input)(m, ifp);
  	goto next;
  bad:
  	m_freem(m);
  	goto next;
  }
  
  /*
   * Take incoming datagram fragment and try to
   * reassemble it into whole datagram.  If a chain for
   * reassembly of this datagram already exists, then it
   * is given as fp; otherwise have to make a chain.
   */
  struct ip *
  ip_reass(ip, fp)
  	register struct ipasfrag *ip;
  	register struct ipq *fp;
  {
  	register struct mbuf *m = dtom(ip);
  	register struct ipasfrag *q;
  	struct mbuf *t;
  	int hlen = ip->ip_hl << 2;
  	int i, next;
  
  	/*
  	 * Presence of header sizes in mbufs
  	 * would confuse code below.
  	 */
  	m->m_off += hlen;
  	m->m_len -= hlen;
  
  	/*
  	 * If first fragment to arrive, create a reassembly queue.
  	 */
  	if (fp == 0) {
  		if ((t = m_get(M_DONTWAIT, MT_FTABLE)) == NULL)
  			goto dropfrag;
  		fp = mtod(t, struct ipq *);
  		insque(fp, &ipq);
  		fp->ipq_ttl = IPFRAGTTL;
  		fp->ipq_p = ip->ip_p;
  		fp->ipq_id = ip->ip_id;
  		fp->ipq_next = fp->ipq_prev = (struct ipasfrag *)fp;
  		fp->ipq_src = ((struct ip *)ip)->ip_src;
  		fp->ipq_dst = ((struct ip *)ip)->ip_dst;
  		q = (struct ipasfrag *)fp;
  		goto insert;
  	}
  
  	/*
  	 * Find a segment which begins after this one does.
  	 */
  	for (q = fp->ipq_next; q != (struct ipasfrag *)fp; q = q->ipf_next)
  		if (q->ip_off > ip->ip_off)
  			break;
  
  	/*
  	 * If there is a preceding segment, it may provide some of
  	 * our data already.  If so, drop the data from the incoming
  	 * segment.  If it provides all of our data, drop us.
  	 */
  	if (q->ipf_prev != (struct ipasfrag *)fp) {
  		i = q->ipf_prev->ip_off + q->ipf_prev->ip_len - ip->ip_off;
  		if (i > 0) {
  			if (i >= ip->ip_len)
  				goto dropfrag;
  			m_adj(dtom(ip), i);
  			ip->ip_off += i;
  			ip->ip_len -= i;
  		}
  	}
  
  	/*
  	 * While we overlap succeeding segments trim them or,
  	 * if they are completely covered, dequeue them.
  	 */
  	while (q != (struct ipasfrag *)fp && ip->ip_off + ip->ip_len > q->ip_off) {
  		i = (ip->ip_off + ip->ip_len) - q->ip_off;
  		if (i < q->ip_len) {
  			q->ip_len -= i;
  			q->ip_off += i;
  			m_adj(dtom(q), i);
  			break;
  		}
  		q = q->ipf_next;
  		m_freem(dtom(q->ipf_prev));
  		ip_deq(q->ipf_prev);
  	}
  
  insert:
  	/*
  	 * Stick new segment in its place;
  	 * check for complete reassembly.
  	 */
  	ip_enq(ip, q->ipf_prev);
  	next = 0;
  	for (q = fp->ipq_next; q != (struct ipasfrag *)fp; q = q->ipf_next) {
  		if (q->ip_off != next)
  			return (0);
  		next += q->ip_len;
  	}
  	if (q->ipf_prev->ipf_mff)
  		return (0);
  
  	/*
  	 * Reassembly is complete; concatenate fragments.
  	 */
  	q = fp->ipq_next;
  	m = dtom(q);
  	t = m->m_next;
  	m->m_next = 0;
  	m_cat(m, t);
  	q = q->ipf_next;
  	while (q != (struct ipasfrag *)fp) {
  		t = dtom(q);
  		q = q->ipf_next;
  		m_cat(m, t);
  	}
  
  	/*
  	 * Create header for new ip packet by
  	 * modifying header of first packet;
  	 * dequeue and discard fragment reassembly header.
  	 * Make header visible.
  	 */
  	ip = fp->ipq_next;
  	ip->ip_len = next;
  	((struct ip *)ip)->ip_src = fp->ipq_src;
  	((struct ip *)ip)->ip_dst = fp->ipq_dst;
  	remque(fp);
  	(void) m_free(dtom(fp));
  	m = dtom(ip);
  	m->m_len += (ip->ip_hl << 2);
  	m->m_off -= (ip->ip_hl << 2);
  	return ((struct ip *)ip);
  
  dropfrag:
  	ipstat.ips_fragdropped++;
  	m_freem(m);
  	return (0);
  }
  
  /*
   * Free a fragment reassembly header and all
   * associated datagrams.
   */
  ip_freef(fp)
  	struct ipq *fp;
  {
  	register struct ipasfrag *q, *p;
  
  	for (q = fp->ipq_next; q != (struct ipasfrag *)fp; q = p) {
  		p = q->ipf_next;
  		ip_deq(q);
  		m_freem(dtom(q));
  	}
  	remque(fp);
  	(void) m_free(dtom(fp));
  }
  
  /*
   * Put an ip fragment on a reassembly chain.
   * Like insque, but pointers in middle of structure.
   */
  ip_enq(p, prev)
  	register struct ipasfrag *p, *prev;
  {
  
  	p->ipf_prev = prev;
  	p->ipf_next = prev->ipf_next;
  	prev->ipf_next->ipf_prev = p;
  	prev->ipf_next = p;
  }
  
  /*
   * To ip_enq as remque is to insque.
   */
  ip_deq(p)
  	register struct ipasfrag *p;
  {
  
  	p->ipf_prev->ipf_next = p->ipf_next;
  	p->ipf_next->ipf_prev = p->ipf_prev;
  }
  
  /*
   * IP timer processing;
   * if a timer expires on a reassembly
   * queue, discard it.
   */
  ip_slowtimo()
  {
  	register struct ipq *fp;
  	int s = splnet();
  
  	fp = ipq.next;
  	if (fp == 0) {
  		splx(s);
  		return;
  	}
  	while (fp != &ipq) {
  		--fp->ipq_ttl;
  		fp = fp->next;
  		if (fp->prev->ipq_ttl == 0) {
  			ipstat.ips_fragtimeout++;
  			ip_freef(fp->prev);
  		}
  	}
  	splx(s);
  }
  
  /*
   * Drain off all datagram fragments.
   */
  ip_drain()
  {
  
  	while (ipq.next != &ipq) {
  		ipstat.ips_fragdropped++;
  		ip_freef(ipq.next);
  	}
  }
  
  extern struct in_ifaddr *ifptoia();
  struct in_ifaddr *ip_rtaddr();
  
  /*
   * Do option processing on a datagram,
   * possibly discarding it if bad options
   * are encountered.
   */
  ip_dooptions(ip, ifp)
  	register struct ip *ip;
  	struct ifnet *ifp;
  {
  	register u_char *cp;
  	int opt, optlen, cnt, off, code, type = ICMP_PARAMPROB, forward = 0;
  	register struct ip_timestamp *ipt;
  	register struct in_ifaddr *ia;
  	struct in_addr *sin;
  	n_time ntime, iptime();
  
  	cp = (u_char *)(ip + 1);
  	cnt = (ip->ip_hl << 2) - sizeof (struct ip);
  	for (; cnt > 0; cnt -= optlen, cp += optlen) {
  		opt = UCHAR(cp[IPOPT_OPTVAL]);
  		if (opt == IPOPT_EOL)
  			break;
  		if (opt == IPOPT_NOP)
  			optlen = 1;
  		else {
  			optlen = UCHAR(cp[IPOPT_OLEN]);
  			if (optlen <= 0 || optlen > cnt) {
  				code = &cp[IPOPT_OLEN] - (u_char *)ip;
  				goto bad;
  			}
  		}
  		switch (opt) {
  
  		default:
  			break;
  
  		/*
  		 * Source routing with record.
  		 * Find interface with current destination address.
  		 * If none on this machine then drop if strictly routed,
  		 * or do nothing if loosely routed.
  		 * Record interface address and bring up next address
  		 * component.  If strictly routed make sure next
  		 * address on directly accessible net.
  		 */
  		case IPOPT_LSRR:
  		case IPOPT_SSRR:
  			if ((off = cp[IPOPT_OFFSET]) < IPOPT_MINOFF) {
  				code = &cp[IPOPT_OFFSET] - (u_char *)ip;
  				goto bad;
  			}
  			ipaddr.sin_addr = ip->ip_dst;
  			ia = (struct in_ifaddr *)
  				ifa_ifwithaddr((struct sockaddr *)&ipaddr);
  			if (ia == 0) {
  				if (opt == IPOPT_SSRR) {
  					type = ICMP_UNREACH;
  					code = ICMP_UNREACH_SRCFAIL;
  					goto bad;
  				}
  				/*
  				 * Loose routing, and not at next destination
  				 * yet; nothing to do except forward.
  				 */
  				break;
  			}
  			off--;			/* 0 origin */
  			if (off > optlen - sizeof(struct in_addr)) {
  				/*
  				 * End of source route.  Should be for us.
  				 */
  				save_rte(cp, ip->ip_src);
  				break;
  			}
  			/*
  			 * locate outgoing interface
  			 */
  			bcopy((caddr_t)(cp + off), (caddr_t)&ipaddr.sin_addr,
  			    sizeof(ipaddr.sin_addr));
  			if ((opt == IPOPT_SSRR &&
  			    in_iaonnetof(in_netof(ipaddr.sin_addr)) == 0) ||
  			    (ia = ip_rtaddr(ipaddr.sin_addr)) == 0) {
  				type = ICMP_UNREACH;
  				code = ICMP_UNREACH_SRCFAIL;
  				goto bad;
  			}
  			ip->ip_dst = ipaddr.sin_addr;
  			bcopy((caddr_t)&(IA_SIN(ia)->sin_addr),
  			    (caddr_t)(cp + off), sizeof(struct in_addr));
  			cp[IPOPT_OFFSET] += sizeof(struct in_addr);
  /*
   * Since 2.11 will never have multicasting so the following line from 4.4
   * is effectively always 1.
  */
  			forward = !IN_MULTICAST(ip->ip_dst.s_addr);
  			break;
  
  		case IPOPT_RR:
  			if ((off = cp[IPOPT_OFFSET]) < IPOPT_MINOFF) {
  				code = &cp[IPOPT_OFFSET] - (u_char *)ip;
  				goto bad;
  			}
  			/*
  			 * If no space remains, ignore.
  			 */
  			off--;			/* 0 origin */
  			if (off > optlen - sizeof(struct in_addr))
  				break;
  			bcopy((caddr_t)(&ip->ip_dst), (caddr_t)&ipaddr.sin_addr,
  			    sizeof(ipaddr.sin_addr));
  			/*
  			 * locate outgoing interface
  			 */
  			if ((ia = ip_rtaddr(ipaddr.sin_addr)) == 0) {
  				type = ICMP_UNREACH;
  				code = ICMP_UNREACH_HOST;
  				goto bad;
  			}
  			bcopy((caddr_t)&(IA_SIN(ia)->sin_addr),
  			    (caddr_t)(cp + off), sizeof(struct in_addr));
  			cp[IPOPT_OFFSET] += sizeof(struct in_addr);
  			break;
  
  		case IPOPT_TS:
  			code = cp - (u_char *)ip;
  			ipt = (struct ip_timestamp *)cp;
  			if (ipt->ipt_len < 5)
  				goto bad;
  			if (ipt->ipt_ptr > ipt->ipt_len - sizeof (long)) {
  				if (++ipt->ipt_oflw == 0)
  					goto bad;
  				break;
  			}
  			sin = (struct in_addr *)(cp + ipt->ipt_ptr - 1);
  			switch (ipt->ipt_flg) {
  
  			case IPOPT_TS_TSONLY:
  				break;
  
  			case IPOPT_TS_TSANDADDR:
  				if (ipt->ipt_ptr + sizeof(n_time) +
  				    sizeof(struct in_addr) > ipt->ipt_len)
  					goto bad;
  				ia = ifptoia(ifp);
  				bcopy((caddr_t)&IA_SIN(ia)->sin_addr,
  				    (caddr_t)sin, sizeof(struct in_addr));
  				ipt->ipt_ptr += sizeof(struct in_addr);
  				break;
  
  			case IPOPT_TS_PRESPEC:
  				if (ipt->ipt_ptr + sizeof(n_time) +
  				    sizeof(struct in_addr) > ipt->ipt_len)
  					goto bad;
  				bcopy((caddr_t)sin, (caddr_t)&ipaddr.sin_addr,
  				    sizeof(struct in_addr));
  				if (ifa_ifwithaddr((struct sockaddr *)&ipaddr) == 0)
  					continue;
  				ipt->ipt_ptr += sizeof(struct in_addr);
  				break;
  
  			default:
  				goto bad;
  			}
  			ntime = iptime();
  			bcopy((caddr_t)&ntime, (caddr_t)cp + ipt->ipt_ptr - 1,
  			    sizeof(n_time));
  			ipt->ipt_ptr += sizeof(n_time);
  		}
  	}
  	if (forward) {
  		if (ipforward_srcrt == 0) {
  			type = ICMP_UNREACH;
  			code = ICMP_UNREACH_SRCFAIL;
  			goto bad;
  		}
  		ip_forward(ip, ifp, 1);
  		return(1);
  	}
  	return (0);
  bad:
  	ip->ip_len -= ip->ip_hl << 2;	/* XXX icmp_error adds in hdr length */
  	icmp_error(ip, type, code, ifp);
  	return (1);
  }
  
  /*
   * Given address of next destination (final or next hop),
   * return internet address info of interface to be used to get there.
   */
  struct in_ifaddr *
  ip_rtaddr(dst)
  	 struct in_addr dst;
  {
  	register struct sockaddr_in *sin;
  	register struct in_ifaddr *ia;
  
  	sin = (struct sockaddr_in *) &ipforward_rt.ro_dst;
  
  	if (ipforward_rt.ro_rt == 0 || dst.s_addr != sin->sin_addr.s_addr) {
  		if (ipforward_rt.ro_rt) {
  			RTFREE(ipforward_rt.ro_rt);
  			ipforward_rt.ro_rt = 0;
  		}
  		sin->sin_family = AF_INET;
  		sin->sin_addr = dst;
  
  		rtalloc(&ipforward_rt);
  	}
  	if (ipforward_rt.ro_rt == 0)
  		return ((struct in_ifaddr *)0);
  	/*
  	 * Find address associated with outgoing interface.
  	 */
  	for (ia = in_ifaddr; ia; ia = ia->ia_next)
  		if (ia->ia_ifp == ipforward_rt.ro_rt->rt_ifp)
  			break;
  	return (ia);
  }
  
  /*
   * Save incoming source route for use in replies,
   * to be picked up later by ip_srcroute if the receiver is interested.
   */
  save_rte(option, dst)
  	u_char *option;
  	struct in_addr dst;
  {
  	unsigned olen;
  
  	olen = option[IPOPT_OLEN];
  	if (olen > sizeof(ip_srcrt) - 1) {
  		if (ipprintfs)
  			printf("save_rte: olen %d\n", olen);
  		return;
  	}
  	bcopy((caddr_t)option, (caddr_t)ip_srcrt.srcopt, olen);
  	ip_nhops = (olen - IPOPT_OFFSET - 1) / sizeof(struct in_addr);
  	ip_srcrt.route[ip_nhops++] = dst;
  }
  
  /*
   * Retrieve incoming source route for use in replies,
   * in the same form used by setsockopt.
   * The first hop is placed before the options, will be removed later.
   */
  struct mbuf *
  ip_srcroute()
  {
  	register struct in_addr *p, *q;
  	register struct mbuf *m;
  
  	if (ip_nhops == 0)
  		return ((struct mbuf *)0);
  	m = m_get(M_DONTWAIT, MT_SOOPTS);
  	if (m == 0)
  		return ((struct mbuf *)0);
  	m->m_len = ip_nhops * sizeof(struct in_addr) + IPOPT_OFFSET + 1 + 1;
  
  	/*
  	 * First save first hop for return route
  	 */
  	p = &ip_srcrt.route[ip_nhops - 1];
  	*(mtod(m, struct in_addr *)) = *p--;
  
  	/*
  	 * Copy option fields and padding (nop) to mbuf.
  	 */
  	ip_srcrt.nop = IPOPT_NOP;
  	bcopy((caddr_t)&ip_srcrt, mtod(m, caddr_t) + sizeof(struct in_addr),
  	    IPOPT_OFFSET + 1 + 1);
  	q = (struct in_addr *)(mtod(m, caddr_t) +
  	    sizeof(struct in_addr) + IPOPT_OFFSET + 1 + 1);
  	/*
  	 * Record return path as an IP source route,
  	 * reversing the path (pointers are now aligned).
  	 */
  	while (p >= ip_srcrt.route)
  		*q++ = *p--;
  	return (m);
  }
  
  /*
   * Strip out IP options, at higher
   * level protocol in the kernel.
   * Second argument is buffer to which options
   * will be moved, and return value is their length.
   */
  ip_stripoptions(ip, mopt)
  	struct ip *ip;
  	struct mbuf *mopt;
  {
  	register int i;
  	register struct mbuf *m;
  	register caddr_t opts;
  	int olen;
  
  	olen = (ip->ip_hl<<2) - sizeof (struct ip);
  	m = dtom(ip);
  	opts = (caddr_t)(ip + 1);
  	if (mopt) {
  		mopt->m_len = olen;
  		mopt->m_off = MMINOFF;
  		bcopy(opts, mtod(mopt, caddr_t), (unsigned)olen);
  	}
  	i = m->m_len - (sizeof (struct ip) + olen);
  	bcopy(opts  + olen, opts, (unsigned)i);
  	m->m_len -= olen;
  	ip->ip_hl = sizeof(struct ip) >> 2;
  }
  
  u_char inetctlerrmap[PRC_NCMDS] = {
  	0,		0,		0,		0,
  	0,		0,		EHOSTDOWN,	EHOSTUNREACH,
  	ENETUNREACH,	EHOSTUNREACH,	ECONNREFUSED,	ECONNREFUSED,
  	EMSGSIZE,	EHOSTUNREACH,	0,		0,
  	0,		0,		0,		0,
  	ENOPROTOOPT
  };
  
  extern	int in_interfaces;
  
  /*
   * Forward a packet.  If some error occurs return the sender
   * an icmp packet.  Note we can't always generate a meaningful
   * icmp message because icmp doesn't have a large enough repertoire
   * of codes and types.
   *
   * If not forwarding (possibly because we have only a single external
   * network), just drop the packet.  This could be confusing if ipforwarding
   * was zero but some routing protocol was advancing us as a gateway
   * to somewhere.  However, we must let the routing protocol deal with that.
   *
   * The srcrt parameter indicates whether the packet is being forwarded
   * via a source route.
   */
  ip_forward(ip, ifp, srcrt)
  	register struct ip *ip;
  	struct ifnet *ifp;
  	int srcrt;
  {
  	register int error, type = 0, code;
  	register struct sockaddr_in *sin;
  	struct mbuf *mcopy;
  	struct in_addr dest;
  
  	dest.s_addr = 0;
  	if (ipprintfs)
  		printf("forward: src %X dst %X ttl %x\n", ntohl(ip->ip_src),
  			ntohl(ip->ip_dst), ip->ip_ttl);
  	ip->ip_id = htons(ip->ip_id);
  	if (in_canforward(ip->ip_dst) == 0) {
  		ipstat.ips_cantforward++;
  		m_freem(dtom(ip));
  		return;
  	}
  	if (ip->ip_ttl < IPTTLDEC) {
  		type = ICMP_TIMXCEED, code = ICMP_TIMXCEED_INTRANS;
  		goto sendicmp;
  	}
  	ip->ip_ttl -= IPTTLDEC;
  
  	sin = (struct sockaddr_in *)&ipforward_rt.ro_dst;
  	if (ipforward_rt.ro_rt == 0 ||
  	    ip->ip_dst.s_addr != sin->sin_addr.s_addr) {
  		if (ipforward_rt.ro_rt) {
  			RTFREE(ipforward_rt.ro_rt);
  			ipforward_rt.ro_rt = 0;
  		}
  		sin->sin_family = AF_INET;
  		sin->sin_addr = ip->ip_dst;
  
  		rtalloc(&ipforward_rt);
  		if (ipforward_rt.ro_rt == 0) {
  			ip->ip_len -= ip->ip_hl << 2;	/* icmp_error assumes this */
  			icmp_error(ip,ICMP_UNREACH,ICMP_UNREACH_HOST,ifp,dest);
  			return;
  		}
  	}
  
  	/*
  	 * Save at most 64 bytes of the packet in case
  	 * we need to generate an ICMP message to the src.
  	 */
  	mcopy = m_copy(dtom(ip), 0, MIN((int)ip->ip_len, 64));
  
  	/*
  	 * If forwarding packet using same interface that it came in on,
  	 * perhaps should send a redirect to sender to shortcut a hop.
  	 * Only send redirect if source is sending directly to us,
  	 * and if packet was not source routed (or has any options).
  	 * Also, don't send redirect if forwarding using a default route
  	 * or a route modfied by a redirect.
  	 */
  #define	satosin(sa)	((struct sockaddr_in *)(sa))
  	if (ipforward_rt.ro_rt && ipforward_rt.ro_rt->rt_ifp == ifp &&
  	    (ipforward_rt.ro_rt->rt_flags & (RTF_DYNAMIC|RTF_MODIFIED)) == 0 &&
  	    satosin(&ipforward_rt.ro_rt->rt_dst)->sin_addr.s_addr != 0 &&
  	    ipsendredirects && !srcrt && ip->ip_hl == (sizeof(struct ip) >> 2)){
  		struct in_ifaddr *ia;
  		u_long src = ntohl(ip->ip_src.s_addr);
  		u_long dst = ntohl(ip->ip_dst.s_addr);
  
  		if ((ia = ifptoia(ifp)) &&
  		   (src & ia->ia_subnetmask) == ia->ia_subnet) {
  		    if (ipforward_rt.ro_rt->rt_flags & RTF_GATEWAY)
  			dest = satosin(&ipforward_rt.ro_rt->rt_gateway)->sin_addr;
  		    else
  			dest = ip->ip_dst;
  		    /*
  		     * If the destination is reached by a route to host,
  		     * is on a subnet of a local net, or is directly
  		     * on the attached net (!), use host redirect.
  		     * (We may be the correct first hop for other subnets.)
  		     */
  		    type = ICMP_REDIRECT;
  		    code = ICMP_REDIRECT_NET;
  		    if ((ipforward_rt.ro_rt->rt_flags & RTF_HOST) ||
  		       (ipforward_rt.ro_rt->rt_flags & RTF_GATEWAY) == 0)
  			code = ICMP_REDIRECT_HOST;
  		    else for (ia = in_ifaddr; ia == ia->ia_next; )
  			if ((dst & ia->ia_netmask) == ia->ia_net) {
  			    if (ia->ia_subnetmask != ia->ia_netmask)
  				    code = ICMP_REDIRECT_HOST;
  			    break;
  			}
  		    if (ipprintfs)
  		        printf("redirect (%d) to %x\n", code, dest);
  		}
  	}
  
  	error = ip_output(dtom(ip), (struct mbuf *)0, &ipforward_rt,
  		IP_FORWARDING);
  	if (error)
  		ipstat.ips_cantforward++;
  	else if (type)
  		ipstat.ips_redirectsent++;
  	else {
  		if (mcopy)
  			m_freem(mcopy);
  		ipstat.ips_forward++;
  		return;
  	}
  	if (mcopy == NULL)
  		return;
  	ip = mtod(mcopy, struct ip *);
  	type = ICMP_UNREACH;
  	switch (error) {
  
  	case 0:				/* forwarded, but need redirect */
  		type = ICMP_REDIRECT;
  		/* code set above */
  		break;
  
  	case ENETUNREACH:
  	case ENETDOWN:
  		if (in_localaddr(ip->ip_dst))
  			code = ICMP_UNREACH_HOST;
  		else
  			code = ICMP_UNREACH_NET;
  		break;
  
  	case EMSGSIZE:
  		code = ICMP_UNREACH_NEEDFRAG;
  		break;
  
  	case EPERM:
  		code = ICMP_UNREACH_PORT;
  		break;
  
  	case ENOBUFS:
  		type = ICMP_SOURCEQUENCH;
  		break;
  
  	case EHOSTDOWN:
  	case EHOSTUNREACH:
  		code = ICMP_UNREACH_HOST;
  		break;
  	}
  sendicmp:
  	ip->ip_len -= ip->ip_hl << 2;	/* icmp_error assumes this */
  	icmp_error(ip, type, code, ifp, dest);
  }
  
  int
  ip_sysctl(name, namelen, oldp, oldlenp, newp, newlen)
  	int *name;
  	u_int namelen;
  	void *oldp;
  	size_t *oldlenp;
  	void *newp;
  	size_t newlen;
  {
  	/* All sysctl names at this level are terminal. */
  	if (namelen != 1)
  		return (ENOTDIR);
  
  	switch (name[0]) {
  	case IPCTL_FORWARDING:
  		return (sysctl_int(oldp, oldlenp, newp, newlen, &ipforwarding));
  	case IPCTL_SENDREDIRECTS:
  		return (sysctl_int(oldp, oldlenp, newp, newlen,
  			&ipsendredirects));
  	case IPCTL_DEFTTL:
  		return (sysctl_int(oldp, oldlenp, newp, newlen, &ip_defttl));
  #ifdef notyet
  	case IPCTL_DEFMTU:
  		return (sysctl_int(oldp, oldlenp, newp, newlen, &ip_mtu));
  #endif
  	case IPCTL_FORWSRCRT:
  		return (sysctl_int(oldp, oldlenp, newp, newlen,
  		    &ipforward_srcrt));
  	default:
  		return (EOPNOTSUPP);
  	}
  	/* NOTREACHED */
  }
  