text: /*
   * Copyright (c) 1982, 1986, 1988, 1993
   *	The Regents of the University of California.  All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 3. All advertising materials mentioning features or use of this software
   *    must display the following acknowledgement:
   *	This product includes software developed by the University of
   *	California, Berkeley and its contributors.
   * 4. Neither the name of the University nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   *
   * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   *
   *	@(#)if_ether.c	8.1 (Berkeley) 6/10/93
   * $FreeBSD: src/sys/netinet/if_ether.c,v 1.64.2.28 2004/10/26 17:36:16 bms Exp $
   */
  
  /*
   * Ethernet address resolution protocol.
   * TODO:
   *	add "inuse/lock" bit (or ref. count) along with valid bit
   */
  
  #include "opt_inet.h"
  #include "opt_bdg.h"
  
  #include <sys/param.h>
  #include <sys/kernel.h>
  #include <sys/queue.h>
  #include <sys/sysctl.h>
  #include <sys/systm.h>
  #include <sys/mbuf.h>
  #include <sys/malloc.h>
  #include <sys/socket.h>
  #include <sys/syslog.h>
  
  #include <net/if.h>
  #include <net/if_dl.h>
  #include <net/if_types.h>
  #include <net/route.h>
  #include <net/netisr.h>
  #include <net/if_llc.h>
  #ifdef BRIDGE
  #include <net/ethernet.h>
  #include <net/bridge.h>
  #endif
  
  #include <netinet/in.h>
  #include <netinet/in_var.h>
  #include <netinet/if_ether.h>
  
  #include <net/if_arc.h>
  #include <net/iso88025.h>
  
  #define SIN(s) ((struct sockaddr_in *)s)
  #define SDL(s) ((struct sockaddr_dl *)s)
  
  SYSCTL_DECL(_net_link_ether);
  SYSCTL_NODE(_net_link_ether, PF_INET, inet, CTLFLAG_RW, 0, "");
  
  /* timer values */
  static int arpt_prune = (5*60*1); /* walk list every 5 minutes */
  static int arpt_keep = (20*60); /* once resolved, good for 20 more minutes */
  static int arpt_down = 20;	/* once declared down, don't send for 20 sec */
  
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, prune_intvl, CTLFLAG_RW,
  	   &arpt_prune, 0, "");
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, max_age, CTLFLAG_RW, 
  	   &arpt_keep, 0, "");
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, host_down_time, CTLFLAG_RW,
  	   &arpt_down, 0, "");
  
  #define	rt_expire rt_rmx.rmx_expire
  
  struct llinfo_arp {
  	LIST_ENTRY(llinfo_arp) la_le;
  	struct	rtentry *la_rt;
  	struct	mbuf *la_hold;	/* last packet until resolved/timeout */
  	u_short	la_preempt;	/* #times we QUERIED before entry expiration */
  	u_short	la_asked;	/* #times we QUERIED following expiration */
  #define la_timer la_rt->rt_rmx.rmx_expire /* deletion time in seconds */
  };
  
  static	LIST_HEAD(, llinfo_arp) llinfo_arp;
  
  struct	ifqueue arpintrq = {0, 0, 0, 50};
  static int	arp_inuse, arp_allocated, arpinit_done;
  
  static int	arp_maxtries = 5;
  static int	useloopback = 1; /* use loopback interface for local traffic */
  static int	arp_proxyall = 0;
  
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, maxtries, CTLFLAG_RW,
  	   &arp_maxtries, 0, "");
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, useloopback, CTLFLAG_RW,
  	   &useloopback, 0, "");
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, proxyall, CTLFLAG_RW,
  	   &arp_proxyall, 0, "");
  
  static void	arp_rtrequest __P((int, struct rtentry *, struct rt_addrinfo *));
  static void	arprequest __P((struct ifnet *,
  			struct in_addr *, struct in_addr *, u_char *));
  static void	arpintr __P((void));
  static void	arptfree __P((struct llinfo_arp *));
  static void	arptimer __P((void *));
  static void	arp_rtdrain __P((struct rtentry *, struct rttimer *));
  static struct llinfo_arp
  		*arplookup __P((u_long, int, int));
  #ifdef INET
  static void	in_arpinput __P((struct mbuf *));
  #endif
  
  u_char arcbroadcastaddr = 0;
  
  #define IF_BCASTADDR(ifp)					\
  	((ifp)->if_type == IFT_ARCNET ?				\
  		&arcbroadcastaddr : etherbroadcastaddr)
  
  /*
   * Timeout routine.  Age arp_tab entries periodically.
   */
  /* ARGSUSED */
  static void
  arptimer(ignored_arg)
  	void *ignored_arg;
  {
  	int s = splnet();
  	register struct llinfo_arp *la = LIST_FIRST(&llinfo_arp);
  	struct llinfo_arp *ola;
  
  	timeout(arptimer, (caddr_t)0, arpt_prune * hz);
  	while ((ola = la) != 0) {
  		register struct rtentry *rt = la->la_rt;
  		la = LIST_NEXT(la, la_le);
  		if (rt->rt_expire && rt->rt_expire <= time_second)
  			arptfree(ola); /* timer has expired, clear */
  	}
  	splx(s);
  }
  
  /*
   * Parallel to llc_rtrequest.
   */
  static void
  arp_rtrequest(req, rt, info)
  	int req;
  	register struct rtentry *rt;
  	struct rt_addrinfo *info;
  {
  	register struct sockaddr *gate = rt->rt_gateway;
  	register struct llinfo_arp *la = (struct llinfo_arp *)rt->rt_llinfo;
  	static struct sockaddr_dl null_sdl = {sizeof(null_sdl), AF_LINK};
  	int mine = 0;
  
  	if (!arpinit_done) {
  		arpinit_done = 1;
  		timeout(arptimer, (caddr_t)0, hz);
  	}
  	if (rt->rt_flags & RTF_GATEWAY)
  		return;
  	switch (req) {
  
  	case RTM_ADD:
  		/*
  		 * XXX: If this is a manually added route to interface
  		 * such as older version of routed or gated might provide,
  		 * restore cloning bit.
  		 */
  		if ((rt->rt_flags & RTF_HOST) == 0 &&
  		    rt_mask(rt) != NULL &&
  		    SIN(rt_mask(rt))->sin_addr.s_addr != 0xffffffff)
  			rt->rt_flags |= RTF_CLONING;
  		if (rt->rt_flags & RTF_CLONING) {
  			/*
  			 * Case 1: This route should come from a route to iface.
  			 */
  			rt_setgate(rt, rt_key(rt),
  					(struct sockaddr *)&null_sdl);
  			gate = rt->rt_gateway;
  			SDL(gate)->sdl_type = rt->rt_ifp->if_type;
  			SDL(gate)->sdl_index = rt->rt_ifp->if_index;
  			rt->rt_expire = time_second;
  			break;
  		}
  		/* Announce a new entry if requested. */
  		if (rt->rt_flags & RTF_ANNOUNCE)
  			arprequest(rt->rt_ifp,
  			    &SIN(rt_key(rt))->sin_addr,
  			    &SIN(rt_key(rt))->sin_addr,
  			    (u_char *)LLADDR(SDL(gate)));
  		/*FALLTHROUGH*/
  	case RTM_RESOLVE:
  		if (gate->sa_family != AF_LINK ||
  		    gate->sa_len < sizeof(null_sdl)) {
  			log(LOG_DEBUG, "arp_rtrequest: bad gateway value\n");
  			break;
  		}
  		SDL(gate)->sdl_type = rt->rt_ifp->if_type;
  		SDL(gate)->sdl_index = rt->rt_ifp->if_index;
  		if (la != 0)
  			break; /* This happens on a route change */
  		/*
  		 * Case 2:  This route may come from cloning, or a manual route
  		 * add with a LL address.
  		 */
  		R_Malloc(la, struct llinfo_arp *, sizeof(*la));
  		rt->rt_llinfo = (caddr_t)la;
  		if (la == 0) {
  			log(LOG_DEBUG, "arp_rtrequest: malloc failed\n");
  			break;
  		}
  		arp_inuse++, arp_allocated++;
  		Bzero(la, sizeof(*la));
  		la->la_rt = rt;
  		rt->rt_flags |= RTF_LLINFO;
  		LIST_INSERT_HEAD(&llinfo_arp, la, la_le);
  
  #ifdef INET
  		/*
  		 * This keeps the multicast addresses from showing up
  		 * in `arp -a' listings as unresolved.  It's not actually
  		 * functional.  Then the same for broadcast.
  		 */
  		if (IN_MULTICAST(ntohl(SIN(rt_key(rt))->sin_addr.s_addr))
  		&&  rt->rt_ifp->if_type != IFT_ARCNET) {
  			ETHER_MAP_IP_MULTICAST(&SIN(rt_key(rt))->sin_addr,
  					       LLADDR(SDL(gate)));
  			SDL(gate)->sdl_alen = 6;
  			rt->rt_expire = 0;
  		}
  		if (in_broadcast(SIN(rt_key(rt))->sin_addr, rt->rt_ifp)) {
  			memcpy(LLADDR(SDL(gate)), IF_BCASTADDR(rt->rt_ifp),
  			       rt->rt_ifp->if_addrlen);
  			SDL(gate)->sdl_alen = rt->rt_ifp->if_addrlen;
  			rt->rt_expire = 0;
  		}
  #endif
  
  		if (SIN(rt_key(rt))->sin_addr.s_addr ==
  		    (IA_SIN(rt->rt_ifa))->sin_addr.s_addr) {
  		    /*
  		     * This test used to be
  		     *	if (loif.if_flags & IFF_UP)
  		     * It allowed local traffic to be forced
  		     * through the hardware by configuring the loopback down.
  		     * However, it causes problems during network configuration
  		     * for boards that can't receive packets they send.
  		     * It is now necessary to clear "useloopback" and remove
  		     * the route to force traffic out to the hardware.
  		     */
  			mine = 1;
  			rt->rt_expire = 0;
  			Bcopy(IF_LLADDR(rt->rt_ifp), LLADDR(SDL(gate)),
  			      SDL(gate)->sdl_alen = rt->rt_ifp->if_addrlen);
  			if (useloopback)
  				rt->rt_ifp = loif;
  
  		}
  
  		/*
  		 * if this is a cached route, which is very likely,
  		 * put it in the timer queue.
  		 */
  		if (!(rt->rt_flags & (RTF_STATIC | RTF_ANNOUNCE)) && !mine)
  			rt_add_cache(rt, arp_rtdrain);
  
  		break;
  
  	case RTM_DELETE:
  		if (la == 0)
  			break;
  		arp_inuse--;
  		LIST_REMOVE(la, la_le);
  		rt->rt_llinfo = 0;
  		rt->rt_flags &= ~RTF_LLINFO;
  		if (la->la_hold)
  			m_freem(la->la_hold);
  		Free((caddr_t)la);
  	}
  }
  
  static void
  arp_rtdrain(rt, rtt)
  	struct rtentry *rt;
  	struct rttimer *rtt;
  {
  	struct llinfo_arp *la;
  	struct sockaddr_dl *sdl;
  
  	if ((la = (struct llinfo_arp *)rt->rt_llinfo) == NULL) {
  		/*
  		 * This case can happen when rt_fixdelete() invalidated the
  		 * route entry but there are still positive references to
  		 * this entry.
  		 */
  		return;
  	}
  
  	/* if the arp entry has been resolved, just keep it. */
  	sdl = (struct sockaddr_dl *)rt->rt_gateway;
  	if (sdl && sdl->sdl_family == AF_LINK && /* check just in case */
  	    sdl->sdl_alen != 0) {
  		rt_add_cache(rt, arp_rtdrain);
  		return;
  	}
  
  	arptfree(la);
  
  	return;			/* the caller will free rtt */
  }
  
  /*
   * Broadcast an ARP request. Caller specifies:
   *	- arp header source ip address
   *	- arp header target ip address
   *	- arp header source ethernet address
   */
  static void
  arprequest(ifp, sip, tip, enaddr)
  	register struct ifnet *ifp;
  	register struct in_addr *sip, *tip;
  	register u_char *enaddr;
  {
  	register struct mbuf *m;
  	register struct ether_header *eh;
  	register struct arc_header *arh;
  	register struct arphdr *ah;
  	struct sockaddr sa;
  	static u_char	llcx[] = { 0x82, 0x40, LLC_SNAP_LSAP, LLC_SNAP_LSAP,
  				   LLC_UI, 0x00, 0x00, 0x00, 0x08, 0x06 };
  	u_short ar_hrd;
  
  	if ((m = m_gethdr(M_DONTWAIT, MT_DATA)) == NULL)
  		return;
  	m->m_pkthdr.rcvif = (struct ifnet *)0;
  	switch (ifp->if_type) {
  	case IFT_ARCNET:
  		ar_hrd = htons(ARPHRD_ARCNET);
  
  		m->m_len = arphdr_len2(ifp->if_addrlen, sizeof(struct in_addr));
  		m->m_pkthdr.len = m->m_len;
  		MH_ALIGN(m, m->m_len);
  
  		arh = (struct arc_header *)sa.sa_data;
  		arh->arc_dhost = arcbroadcastaddr;
  		arh->arc_type = ARCTYPE_ARP;
  
  		ah = mtod(m, struct arphdr *);
  		break;
  
  	case IFT_ISO88025:
  		ar_hrd = htons(ARPHRD_IEEE802);
  
  		m->m_len = sizeof(llcx) +
  		    arphdr_len2(ifp->if_addrlen, sizeof(struct in_addr));
  		m->m_pkthdr.len = m->m_len;
  		MH_ALIGN(m, m->m_len);
  
  		(void)memcpy(mtod(m, caddr_t), llcx, sizeof(llcx));
  		(void)memcpy(sa.sa_data, etherbroadcastaddr, 6);
  		(void)memcpy(sa.sa_data + 6, enaddr, 6);
  		sa.sa_data[6] |= TR_RII;
  		sa.sa_data[12] = TR_AC;
  		sa.sa_data[13] = TR_LLC_FRAME;
  
  		ah = (struct arphdr *)(mtod(m, char *) + sizeof(llcx));
  		break;
  	case IFT_FDDI:
  	case IFT_ETHER:
  		/*
  		 * This may not be correct for types not explicitly
  		 * listed, but this is our best guess
  		 */
  	default:
  		ar_hrd = htons(ARPHRD_ETHER);
  
  		m->m_len = arphdr_len2(ifp->if_addrlen, sizeof(struct in_addr));
  		m->m_pkthdr.len = m->m_len;
  		MH_ALIGN(m, m->m_len);
  
  		eh = (struct ether_header *)sa.sa_data;
  		/* if_output will not swap */
  		eh->ether_type = htons(ETHERTYPE_ARP);
  		(void)memcpy(eh->ether_dhost, etherbroadcastaddr,
  		    sizeof(eh->ether_dhost));
  
  		ah = mtod(m, struct arphdr *);
  		break;
  	}
  
  	ah->ar_hrd = ar_hrd;
  	ah->ar_pro = htons(ETHERTYPE_IP);
  	ah->ar_hln = ifp->if_addrlen;		/* hardware address length */
  	ah->ar_pln = sizeof(struct in_addr);	/* protocol address length */
  	ah->ar_op = htons(ARPOP_REQUEST);
  	(void)memcpy(ar_sha(ah), enaddr, ah->ar_hln);
  	memset(ar_tha(ah), 0, ah->ar_hln);
  	(void)memcpy(ar_spa(ah), sip, ah->ar_pln);
  	(void)memcpy(ar_tpa(ah), tip, ah->ar_pln);
  
  	sa.sa_family = AF_UNSPEC;
  	sa.sa_len = sizeof(sa);
  	(*ifp->if_output)(ifp, m, &sa, (struct rtentry *)0);
  }
  
  /*
   * Resolve an IP address into an ethernet address.  If success,
   * desten is filled in.  If there is no entry in arptab,
   * set one up and broadcast a request for the IP address.
   * Hold onto this mbuf and resend it once the address
   * is finally resolved.  A return value of 1 indicates
   * that desten has been filled in and the packet should be sent
   * normally; a 0 return indicates that the packet has been
   * taken over here, either now or for later transmission.
   */
  int
  arpresolve(ifp, rt, m, dst, desten, rt0)
  	register struct ifnet *ifp;
  	register struct rtentry *rt;
  	struct mbuf *m;
  	register struct sockaddr *dst;
  	register u_char *desten;
  	struct rtentry *rt0;
  {
  	struct llinfo_arp *la = 0;
  	struct sockaddr_dl *sdl;
  
  	if (m->m_flags & M_BCAST) {	/* broadcast */
  		(void)memcpy(desten, IF_BCASTADDR(ifp), ifp->if_addrlen);
  		return (1);
  	}
  	if (m->m_flags & M_MCAST && ifp->if_type != IFT_ARCNET) {/* multicast */
  		ETHER_MAP_IP_MULTICAST(&SIN(dst)->sin_addr, desten);
  		return(1);
  	}
  	if (rt)
  		la = (struct llinfo_arp *)rt->rt_llinfo;
  	if (la == 0) {
  		la = arplookup(SIN(dst)->sin_addr.s_addr, 1, 0);
  		if (la)
  			rt = la->la_rt;
  	}
  	if (la == 0 || rt == 0) {
  		log(LOG_DEBUG, "arpresolve: can't allocate llinfo for %s%s%s\n",
  			inet_ntoa(SIN(dst)->sin_addr), la ? "la" : "",
  				rt ? "rt" : "");
  		m_freem(m);
  		return (0);
  	}
  	sdl = SDL(rt->rt_gateway);
  	/*
  	 * Check the address family and length is valid, the address
  	 * is resolved; otherwise, try to resolve.
  	 */
  	if ((rt->rt_expire == 0 || rt->rt_expire > time_second) &&
  	    sdl->sdl_family == AF_LINK && sdl->sdl_alen != 0) {
  		/*
  		 * If entry has an expiry time and it is approaching,
  		 * see if we need to send an ARP request within this
  		 * arpt_down interval.
  		 */
  		if ((rt->rt_expire != 0) &&
  		    (time_second + (arp_maxtries - la->la_preempt) * arpt_down
  		     > rt->rt_expire)) {
  			arprequest(ifp,
  				   &SIN(rt->rt_ifa->ifa_addr)->sin_addr,
  				   &SIN(dst)->sin_addr,
  				   IF_LLADDR(ifp));
  			la->la_preempt++;
  		} 
  
  		bcopy(LLADDR(sdl), desten, sdl->sdl_alen);
  		return 1;
  	}
  	/*
  	 * If ARP is disabled on this interface, stop.
  	 * XXX
  	 * Probably should not allocate empty llinfo struct if we are
  	 * not going to be sending out an arp request.
  	 */
  	if (ifp->if_flags & IFF_NOARP || ifp->if_ipending & IFF_STATICARP) {
  		m_freem(m);
  		return (0);
  	}
  	/*
  	 * There is an arptab entry, but no ethernet address
  	 * response yet.  Replace the held mbuf with this
  	 * latest one.
  	 */
  	if (la->la_hold)
  		m_freem(la->la_hold);
  	la->la_hold = m;
  	if (rt->rt_expire) {
  		rt->rt_flags &= ~RTF_REJECT;
  		if (la->la_asked == 0 || rt->rt_expire != time_second) {
  			rt->rt_expire = time_second;
  			if (la->la_asked++ < arp_maxtries) {
  				arprequest(ifp,
  					   &SIN(rt->rt_ifa->ifa_addr)->sin_addr,
  					   &SIN(dst)->sin_addr,
  					   IF_LLADDR(ifp));
  			} else {
  				rt->rt_flags |= RTF_REJECT;
  				rt->rt_expire += arpt_down;
  				la->la_preempt = la->la_asked = 0;
  			}
  
  		}
  	}
  	return (0);
  }
  
  /*
   * Common length and type checks are done here,
   * then the protocol-specific routine is called.
   */
  static void
  arpintr()
  {
  	register struct mbuf *m;
  	register struct arphdr *ar;
  	int s;
  
  	while (arpintrq.ifq_head) {
  		s = splimp();
  		IF_DEQUEUE(&arpintrq, m);
  		splx(s);
  		if (m == 0 || (m->m_flags & M_PKTHDR) == 0)
  			panic("arpintr");
  	
                  if (m->m_len < sizeof(struct arphdr) &&
                      ((m = m_pullup(m, sizeof(struct arphdr))) == NULL)) {
  			log(LOG_ERR, "arp: runt packet -- m_pullup failed\n");
  			continue;
  		}
  		ar = mtod(m, struct arphdr *);
  
  		if (ntohs(ar->ar_hrd) != ARPHRD_ETHER
  		    && ntohs(ar->ar_hrd) != ARPHRD_IEEE802
  		    && ntohs(ar->ar_hrd) != ARPHRD_ARCNET) {
  			log(LOG_ERR,
  			    "arp: unknown hardware address format (0x%2D)\n",
  			    (unsigned char *)&ar->ar_hrd, "");
  			m_freem(m);
  			continue;
  		}
  
  		if (m->m_pkthdr.len < arphdr_len(ar) &&
  		    (m = m_pullup(m, arphdr_len(ar))) == NULL) {
  			log(LOG_ERR, "arp: runt packet\n");
  			m_freem(m);
  			continue;
  		}
  
  		switch (ntohs(ar->ar_pro)) {
  #ifdef INET
  			case ETHERTYPE_IP:
  				in_arpinput(m);
  				continue;
  #endif
  		}
  		m_freem(m);
  	}
  }
  
  #ifdef INET
  /*
   * ARP for Internet protocols on 10 Mb/s Ethernet.
   * Algorithm is that given in RFC 826.
   * In addition, a sanity check is performed on the sender
   * protocol address, to catch impersonators.
   * We no longer handle negotiations for use of trailer protocol:
   * Formerly, ARP replied for protocol type ETHERTYPE_TRAIL sent
   * along with IP replies if we wanted trailers sent to us,
   * and also sent them in response to IP replies.
   * This allowed either end to announce the desire to receive
   * trailer packets.
   * We no longer reply to requests for ETHERTYPE_TRAIL protocol either,
   * but formerly didn't normally send requests.
   */
  static int log_arp_wrong_iface = 1;
  static int log_arp_movements = 1;
  
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, log_arp_wrong_iface, CTLFLAG_RW,
  	&log_arp_wrong_iface, 0,
  	"log arp packets arriving on the wrong interface");
  SYSCTL_INT(_net_link_ether_inet, OID_AUTO, log_arp_movements, CTLFLAG_RW,
  	&log_arp_movements, 0,
  	"log arp replies from MACs different than the one in the cache");
  
  
  static void
  in_arpinput(m)
  	struct mbuf *m;
  {
  	register struct arphdr *ah;
  	register struct ifnet *ifp = m->m_pkthdr.rcvif;
  	struct ether_header *eh;
  	struct arc_header *arh;
  	struct iso88025_header *th = (struct iso88025_header *)0;
  	struct iso88025_sockaddr_dl_data *trld;
  	register struct llinfo_arp *la = 0;
  	register struct rtentry *rt;
  	struct ifaddr *ifa;
  	struct in_ifaddr *ia;
  	struct sockaddr_dl *sdl;
  	struct sockaddr sa;
  	struct in_addr isaddr, itaddr, myaddr;
  	int op, rif_len;
  	int req_len;
  
  	req_len = arphdr_len2(ifp->if_addrlen, sizeof(struct in_addr));
  	if (m->m_len < req_len && (m = m_pullup(m, req_len)) == NULL) {
  		log(LOG_ERR, "in_arp: runt packet -- m_pullup failed\n");
  		return;
  	}
  
  	ah = mtod(m, struct arphdr *);
  	op = ntohs(ah->ar_op);
  	(void)memcpy(&isaddr, ar_spa(ah), sizeof (isaddr));
  	(void)memcpy(&itaddr, ar_tpa(ah), sizeof (itaddr));
  #ifdef BRIDGE
  #define BRIDGE_TEST (do_bridge)
  #else
  #define BRIDGE_TEST (0) /* cc will optimise the test away */
  #endif
  	/*
  	 * For a bridge, we want to check the address irrespective
  	 * of the receive interface. (This will change slightly
  	 * when we have clusters of interfaces).
  	 */
  	LIST_FOREACH(ia, INADDR_HASH(itaddr.s_addr), ia_hash)
  		if ((BRIDGE_TEST || (ia->ia_ifp == ifp)) &&
  		    itaddr.s_addr == ia->ia_addr.sin_addr.s_addr)
  			goto match;
  	LIST_FOREACH(ia, INADDR_HASH(isaddr.s_addr), ia_hash)
  		if ((BRIDGE_TEST || (ia->ia_ifp == ifp)) &&
  		    isaddr.s_addr == ia->ia_addr.sin_addr.s_addr)
  			goto match;
  	/*
  	 * No match, use the first inet address on the receive interface
  	 * as a dummy address for the rest of the function.
  	 */
  	TAILQ_FOREACH(ifa, &ifp->if_addrhead, ifa_link)
  		if (ifa->ifa_addr && ifa->ifa_addr->sa_family == AF_INET) {
  			ia = ifatoia(ifa);
  			goto match;
  		}
  	/*
  	 * If bridging, fall back to using any inet address.
  	 * This is probably incorrect, the right way being try to match
  	 * addresses for interfaces in the same cluster, so if we
  	 * get here we should always drop the packet.
  	 */
  	if (!BRIDGE_TEST ||
  	    (ia = TAILQ_FIRST(&in_ifaddrhead)) == NULL) {
  		m_freem(m);
  		return;
  	}
  match:
  	myaddr = ia->ia_addr.sin_addr;
  	if (!bcmp(ar_sha(ah), IF_LLADDR(ifp), ifp->if_addrlen)) {
  		m_freem(m);	/* it's from me, ignore it. */
  		return;
  	}
  	if (!bcmp(ar_sha(ah), IF_BCASTADDR(ifp), ifp->if_addrlen)) {
  		log(LOG_ERR,
  		    "arp: link address is broadcast for IP address %s!\n",
  		    inet_ntoa(isaddr));
  		m_freem(m);
  		return;
  	}
  	if (isaddr.s_addr == myaddr.s_addr) {
  		log(LOG_ERR,
  		   "arp: %*D is using my IP address %s!\n",
  		   ifp->if_addrlen, (u_char *)ar_sha(ah), ":",
  		   inet_ntoa(isaddr));
  		itaddr = myaddr;
  		goto reply;
  	}
  	if (ifp->if_ipending & IFF_STATICARP)
  		goto reply;
  	la = arplookup(isaddr.s_addr, itaddr.s_addr == myaddr.s_addr, 0);
  	if (la && (rt = la->la_rt) && (sdl = SDL(rt->rt_gateway))) {
  		/* the following is not an error when doing bridging */
  		if (!BRIDGE_TEST && rt->rt_ifp != ifp) {
  		    if (log_arp_wrong_iface)
  			log(LOG_ERR, "arp: %s is on %s%d but got reply from %*D on %s%d\n",
  			    inet_ntoa(isaddr),
  			    rt->rt_ifp->if_name, rt->rt_ifp->if_unit,
  			    ifp->if_addrlen, (u_char *)ar_sha(ah), ":",
  			    ifp->if_name, ifp->if_unit);
  		    goto reply;
  		}
  		if (sdl->sdl_alen &&
  		    bcmp(ar_sha(ah), LLADDR(sdl), sdl->sdl_alen)) {
  			if (rt->rt_expire) {
  			    if (log_arp_movements)
  				log(LOG_INFO, "arp: %s moved from %*D to %*D on %s%d\n",
  				    inet_ntoa(isaddr),
  				    ifp->if_addrlen, (u_char *)LLADDR(sdl), ":",
  				    ifp->if_addrlen, (u_char *)ar_sha(ah), ":",
  				    ifp->if_name, ifp->if_unit);
  			} else {
  			    log(LOG_ERR,
  				"arp: %*D attempts to modify permanent entry for %s on %s%d\n",
  				ifp->if_addrlen, (u_char *)ar_sha(ah), ":",
  				inet_ntoa(isaddr), ifp->if_name, ifp->if_unit);
  			    goto reply;
  			}
  		}
  		/*
  		 * sanity check for the address length.
  		 * XXX this does not work for protocols with variable address
  		 * length. -is
  		 */
  		if (sdl->sdl_alen &&
  		    sdl->sdl_alen != ah->ar_hln) {
  			log(LOG_WARNING,
  			    "arp from %*D: new addr len %d, was %d",
  			    ifp->if_addrlen, (u_char *) ar_sha(ah), ":",
  			    ah->ar_hln, sdl->sdl_alen);
  		}
  		if (ifp->if_addrlen != ah->ar_hln) {
  			log(LOG_WARNING,
  			    "arp from %*D: addr len: new %d, i/f %d (ignored)",
  			    ifp->if_addrlen, (u_char *) ar_sha(ah), ":",
  			    ah->ar_hln, ifp->if_addrlen);
  			goto reply;
  		}
  		(void)memcpy(LLADDR(sdl), ar_sha(ah),
  		    sdl->sdl_alen = ah->ar_hln);
  		/*
  		 * If we receive an arp from a token-ring station over
  		 * a token-ring nic then try to save the source
  		 * routing info.
  		 */
  		if (ifp->if_type == IFT_ISO88025) {
  			th = (struct iso88025_header *)m->m_pkthdr.header;
  			trld = SDL_ISO88025(sdl);
  			rif_len = TR_RCF_RIFLEN(th->rcf);
  			if ((th->iso88025_shost[0] & TR_RII) &&
  			    (rif_len > 2)) {
  				trld->trld_rcf = th->rcf;
  				trld->trld_rcf ^= htons(TR_RCF_DIR);
  				memcpy(trld->trld_route, th->rd, rif_len - 2);
  				trld->trld_rcf &= ~htons(TR_RCF_BCST_MASK);
  				/*
  				 * Set up source routing information for
  				 * reply packet (XXX)
  				 */
  				m->m_data -= rif_len;
  				m->m_len  += rif_len;
  				m->m_pkthdr.len += rif_len;
  			} else {
  				th->iso88025_shost[0] &= ~TR_RII;
  				trld->trld_rcf = 0;
  			}
  			m->m_data -= 8;
  			m->m_len  += 8;
  			m->m_pkthdr.len += 8;
  			th->rcf = trld->trld_rcf;
  		}
  		if (rt->rt_expire)
  			rt->rt_expire = time_second + arpt_keep;
  		rt->rt_flags &= ~RTF_REJECT;
  		la->la_preempt = la->la_asked = 0;
  		if (la->la_hold) {
  			(*ifp->if_output)(ifp, la->la_hold,
  				rt_key(rt), rt);
  			la->la_hold = 0;
  		}
  	}
  reply:
  	if (op != ARPOP_REQUEST) {
  		m_freem(m);
  		return;
  	}
  	if (itaddr.s_addr == myaddr.s_addr) {
  		/* I am the target */
  		(void)memcpy(ar_tha(ah), ar_sha(ah), ah->ar_hln);
  		(void)memcpy(ar_sha(ah), IF_LLADDR(ifp), ah->ar_hln);
  	} else {
  		la = arplookup(itaddr.s_addr, 0, SIN_PROXY);
  		if (la == NULL) {
  			struct sockaddr_in sin;
  
  			if (!arp_proxyall) {
  				m_freem(m);
  				return;
  			}
  
  			bzero(&sin, sizeof sin);
  			sin.sin_family = AF_INET;
  			sin.sin_len = sizeof sin;
  			sin.sin_addr = itaddr;
  
  			rt = rtalloc1((struct sockaddr *)&sin, 0, 0UL);
  			if (!rt) {
  				m_freem(m);
  				return;
  			}
  			/*
  			 * Don't send proxies for nodes on the same interface
  			 * as this one came out of, or we'll get into a fight
  			 * over who claims what Ether address.
  			 */
  			if (rt->rt_ifp == ifp) {
  				rtfree(rt);
  				m_freem(m);
  				return;
  			}
  			(void)memcpy(ar_tha(ah), ar_sha(ah), ah->ar_hln);
  			(void)memcpy(ar_sha(ah), IF_LLADDR(ifp), ah->ar_hln);
  			rtfree(rt);
  #ifdef DEBUG_PROXY
  			printf("arp: proxying for %s\n",
  			       inet_ntoa(itaddr));
  #endif
  		} else {
  			rt = la->la_rt;
  			(void)memcpy(ar_tha(ah), ar_sha(ah), ah->ar_hln);
  			sdl = SDL(rt->rt_gateway);
  			(void)memcpy(ar_sha(ah), LLADDR(sdl), ah->ar_hln);
  		}
  	}
  
  	(void)memcpy(ar_tpa(ah), ar_spa(ah), ah->ar_pln);
  	(void)memcpy(ar_spa(ah), &itaddr, ah->ar_pln);
  	ah->ar_op = htons(ARPOP_REPLY);
  	ah->ar_pro = htons(ETHERTYPE_IP); /* let's be sure! */
  	switch (ifp->if_type) {
  	case IFT_ARCNET:
  		arh = (struct arc_header *)sa.sa_data;
  		arh->arc_dhost = *ar_tha(ah);
  		arh->arc_type = ARCTYPE_ARP;
  		break;
  
  	case IFT_ISO88025:
  		/* Re-arrange the source/dest address */
  		memcpy(th->iso88025_dhost, th->iso88025_shost,
  		    sizeof(th->iso88025_dhost));
  		memcpy(th->iso88025_shost, IF_LLADDR(ifp),
  		    sizeof(th->iso88025_shost));
  		/* Set the source routing bit if neccesary */
  		if (th->iso88025_dhost[0] & TR_RII) {
  			th->iso88025_dhost[0] &= ~TR_RII;
  			if (TR_RCF_RIFLEN(th->rcf) > 2)
  				th->iso88025_shost[0] |= TR_RII;
  		}
  		/* Copy the addresses, ac and fc into sa_data */
  		memcpy(sa.sa_data, th->iso88025_dhost,
  		    sizeof(th->iso88025_dhost) * 2);
  		sa.sa_data[(sizeof(th->iso88025_dhost) * 2)] = TR_AC;
  		sa.sa_data[(sizeof(th->iso88025_dhost) * 2) + 1] = TR_LLC_FRAME;
  		break;
  	case IFT_ETHER:
  	case IFT_FDDI:
  	/*
  	 * May not be correct for types not explictly
  	 * listed, but it is our best guess.
  	 */
  	default:
  		eh = (struct ether_header *)sa.sa_data;
  		(void)memcpy(eh->ether_dhost, ar_tha(ah),
  		    sizeof(eh->ether_dhost));
  		eh->ether_type = htons(ETHERTYPE_ARP);
  		break;
  	}
  	sa.sa_family = AF_UNSPEC;
  	sa.sa_len = sizeof(sa);
  	(*ifp->if_output)(ifp, m, &sa, (struct rtentry *)0);
  	return;
  }
  #endif
  
  /*
   * Free an arp entry.
   */
  static void
  arptfree(la)
  	register struct llinfo_arp *la;
  {
  	register struct rtentry *rt = la->la_rt;
  	register struct sockaddr_dl *sdl;
  	if (rt == 0)
  		panic("arptfree");
  	if (rt->rt_refcnt > 0 && (sdl = SDL(rt->rt_gateway)) &&
  	    sdl->sdl_family == AF_LINK) {
  		sdl->sdl_alen = 0;
  		la->la_preempt = la->la_asked = 0;
  		rt->rt_flags &= ~RTF_REJECT;
  		return;
  	}
  	rtrequest(RTM_DELETE, rt_key(rt), (struct sockaddr *)0, rt_mask(rt),
  			0, (struct rtentry **)0);
  }
  /*
   * Lookup or enter a new address in arptab.
   */
  static struct llinfo_arp *
  arplookup(addr, create, proxy)
  	u_long addr;
  	int create, proxy;
  {
  	register struct rtentry *rt;
  	static struct sockaddr_inarp sin = {sizeof(sin), AF_INET };
  	const char *why = 0;
  
  	sin.sin_addr.s_addr = addr;
  	sin.sin_other = proxy ? SIN_PROXY : 0;
  	rt = rtalloc1((struct sockaddr *)&sin, create, 0UL);
  	if (rt == 0)
  		return (0);
  	rt->rt_refcnt--;
  
  	if (rt->rt_flags & RTF_GATEWAY)
  		why = "host is not on local network";
  	else if ((rt->rt_flags & RTF_LLINFO) == 0)
  		why = "could not allocate llinfo";
  	else if (rt->rt_gateway->sa_family != AF_LINK)
  		why = "gateway route is not ours";
  
  	if (why) {
  		if (create)
  			log(LOG_DEBUG, "arplookup %s failed: %s\n",
  			    inet_ntoa(sin.sin_addr), why);
  
  		/* If there are no references to this route, purge it */
  		if (rt->rt_refcnt <= 0 &&
  		    (rt->rt_flags & RTF_WASCLONED) == RTF_WASCLONED) {
  			rtrequest(RTM_DELETE,
  					(struct sockaddr *)rt_key(rt),
  					rt->rt_gateway, rt_mask(rt),
  					rt->rt_flags, 0);
  		}
  		return (0);
  	}
  	return ((struct llinfo_arp *)rt->rt_llinfo);
  }
  
  void
  arp_ifinit(ifp, ifa)
  	struct ifnet *ifp;
  	struct ifaddr *ifa;
  {
  	if (ntohl(IA_SIN(ifa)->sin_addr.s_addr) != INADDR_ANY)
  		arprequest(ifp, &IA_SIN(ifa)->sin_addr,
  				&IA_SIN(ifa)->sin_addr, IF_LLADDR(ifp));
  	ifa->ifa_rtrequest = arp_rtrequest;
  	ifa->ifa_flags |= RTF_CLONING;
  }
  
  static void
  arp_init(void)
  {
  	LIST_INIT(&llinfo_arp);
  	register_netisr(NETISR_ARP, arpintr);
  }
  
  SYSINIT(arp, SI_SUB_PROTO_DOMAIN, SI_ORDER_ANY, arp_init, 0);
  