[apple/xnu.git] / bsd / netinet / if_ether.c

/*
 * Copyright (c) 2000 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 * 
 * The contents of this file constitute Original Code as defined in and
 * are subject to the Apple Public Source License Version 1.1 (the
 * "License").  You may not use this file except in compliance with the
 * License.  Please obtain a copy of the License at
 * http://www.apple.com/publicsource and read it before using this file.
 * 
 * This Original Code and all software distributed under the License are
 * distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT.  Please see the
 * License for the specific language governing rights and limitations
 * under the License.
 * 
 * @APPLE_LICENSE_HEADER_END@
 */
/*
 * 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
 */

/*
 * Ethernet address resolution protocol.
 * TODO:
 *      add "inuse/lock" bit (or ref. count) along with valid bit
 */

#if NOTFB31
#include "opt_inet.h"
#include "opt_bdg.h"
#endif

#include <sys/param.h>
#include <sys/kernel.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/route.h>
#include <net/netisr.h>

#include <netinet/in.h>
#include <netinet/in_var.h>
#include <netinet/if_ether.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 */
        long    la_asked;               /* last time we QUERIED for this addr */
#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;

static int      arp_maxtries = 5;
static int      useloopback = 1; /* use loopback interface for local traffic */
static int      arp_proxyall = 0;
static int      arp_init_called = 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, "");

void    arp_rtrequest __P((int, struct rtentry *, struct sockaddr *));
static void     arprequest __P((struct arpcom *,
                        struct in_addr *, struct in_addr *, u_char *));
void    arpintr __P((void));
static void     arptfree __P((struct llinfo_arp *));
static void     arptimer __P((void *));
static u_char   etherbroadcastaddr[6] = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff };
static struct llinfo_arp
                *arplookup __P((u_long, int, int));
#if INET
static void     in_arpinput __P((struct mbuf *));
#endif

/*
 * Timeout routine.  Age arp_tab entries periodically.
 */
/* ARGSUSED */
static void
arptimer(ignored_arg)
        void *ignored_arg;
{
        int s ;
        register struct llinfo_arp *la;
        struct llinfo_arp *ola;
        boolean_t       funnel_state;


        funnel_state = thread_funnel_set(network_flock, TRUE);
        s = splnet();
        la = llinfo_arp.lh_first;
        
        timeout(arptimer, (caddr_t)0, arpt_prune * hz);
        while ((ola = la) != 0) {
                register struct rtentry *rt = la->la_rt;
                la = la->la_le.le_next;
                if (rt->rt_expire && rt->rt_expire <= time_second)
                        arptfree(ola); /* timer has expired, clear */
        }
        splx(s);
        (void) thread_funnel_set(network_flock, FALSE);

}

/*
 * Parallel to llc_rtrequest.
 */
void
arp_rtrequest(req, rt, sa)
        int req;
        register struct rtentry *rt;
        struct sockaddr *sa;
{
        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};
        static int arpinit_done;

        if (!arpinit_done) {
                arpinit_done = 1;
                LIST_INIT(&llinfo_arp);
                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 &&
                    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((struct arpcom *)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);

#if 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))) {
                        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)), etherbroadcastaddr, 6);
                        SDL(gate)->sdl_alen = 6;
                        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.
                     */
                        rt->rt_expire = 0;
                        Bcopy(((struct arpcom *)rt->rt_ifp)->ac_enaddr,
                                LLADDR(SDL(gate)), SDL(gate)->sdl_alen = 6);
                        if (useloopback)
                                rt->rt_ifp = loif;

                }
                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);
        }
}




/*
 * Broadcast an ARP packet, asking who has addr on interface ac.
 */
void
arpwhohas(ac, addr)
        register struct arpcom *ac;
        register struct in_addr *addr;
{       struct ifnet *ifp = (struct ifnet *)ac;
        struct ifaddr *ifa = TAILQ_FIRST(&ifp->if_addrhead);

        while (ifa)
        {       if (ifa->ifa_addr->sa_family == AF_INET)
                {       arprequest(ac, &SIN(ifa->ifa_addr)->sin_addr, addr, ac->ac_enaddr);
                        return;
                }
        ifa = TAILQ_NEXT(ifa, ifa_link);
        }
        return; /* XXX */
}



/*
 * Broadcast an ARP request. Caller specifies:
 *      - arp header source ip address
 *      - arp header target ip address
 *      - arp header source ethernet address
 */
static void
arprequest(ac, sip, tip, enaddr)
        register struct arpcom *ac;
        register struct in_addr *sip, *tip;
        register u_char *enaddr;
{
        register struct mbuf *m;
        register struct ether_header *eh;
        register struct ether_arp *ea;
        struct sockaddr sa;

        if ((m = m_gethdr(M_DONTWAIT, MT_DATA)) == NULL)
                return;
        m->m_len = sizeof(*ea);
        m->m_pkthdr.len = sizeof(*ea);
        m->m_pkthdr.rcvif = (struct ifnet *)0;
        MH_ALIGN(m, sizeof(*ea));
        ea = mtod(m, struct ether_arp *);
        eh = (struct ether_header *)sa.sa_data;
        bzero((caddr_t)ea, sizeof (*ea));
        (void)memcpy(eh->ether_dhost, etherbroadcastaddr, sizeof(eh->ether_dhost));
        eh->ether_type = htons(ETHERTYPE_ARP);  /* if_output will not swap */
        ea->arp_hrd = htons(ARPHRD_ETHER);
        ea->arp_pro = htons(ETHERTYPE_IP);
        ea->arp_hln = sizeof(ea->arp_sha);      /* hardware address length */
        ea->arp_pln = sizeof(ea->arp_spa);      /* protocol address length */
        ea->arp_op = htons(ARPOP_REQUEST);
        (void)memcpy(ea->arp_sha, enaddr, sizeof(ea->arp_sha));
        (void)memcpy(ea->arp_spa, sip, sizeof(ea->arp_spa));
        (void)memcpy(ea->arp_tpa, tip, sizeof(ea->arp_tpa));
        sa.sa_family = AF_UNSPEC;
        sa.sa_len = sizeof(sa);
        dlil_output((u_long) ac, m, 0, &sa, 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(ac, rt, m, dst, desten, rt0)
        register struct arpcom *ac;
        register struct rtentry *rt;
        struct mbuf *m;
        register struct sockaddr *dst;
        register u_char *desten;
        struct rtentry *rt0;
{
        register struct llinfo_arp *la = 0;
        struct sockaddr_dl *sdl;

        if (m->m_flags & M_BCAST) {     /* broadcast */
                (void)memcpy(desten, etherbroadcastaddr, sizeof(etherbroadcastaddr));
                return (1);
        }
        if (m->m_flags & M_MCAST) {     /* 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) {
                bcopy(LLADDR(sdl), desten, sdl->sdl_alen);
                return 1;
        }
        /*
         * 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(ac,
                                &SIN(rt->rt_ifa->ifa_addr)->sin_addr,
                                &SIN(dst)->sin_addr, ac->ac_enaddr);
                        else {
                                rt->rt_flags |= RTF_REJECT;
                                rt->rt_expire += arpt_down;
                                la->la_asked = 0;
                        }

                }
        }
        return (0);
}

/*
 * Common length and type checks are done here,
 * then the protocol-specific routine is called.
 */
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) &&
                    (ar = mtod(m, struct arphdr *)) &&
                    ntohs(ar->ar_hrd) == ARPHRD_ETHER &&
                    m->m_len >=
                      sizeof(struct arphdr) + 2 * ar->ar_hln + 2 * ar->ar_pln)

                            switch (ntohs(ar->ar_pro)) {

#if INET
                            case ETHERTYPE_IP:
                                    in_arpinput(m);
                                    continue;
#endif
                            }
                m_freem(m);
        }
}

NETISR_SET(NETISR_ARP, arpintr);


#if 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 void
in_arpinput(m)
        struct mbuf *m;
{
        register struct ether_arp *ea;
        register struct arpcom *ac = (struct arpcom *)m->m_pkthdr.rcvif;
        struct ether_header *eh;
        register struct llinfo_arp *la = 0;
        register struct rtentry *rt;
        struct in_ifaddr *ia, *maybe_ia = 0;
        struct sockaddr_dl *sdl;
        struct sockaddr sa;
        struct in_addr isaddr, itaddr, myaddr;
        int op;
        unsigned char buf[18];

        ea = mtod(m, struct ether_arp *);
        op = ntohs(ea->arp_op);
        (void)memcpy(&isaddr, ea->arp_spa, sizeof (isaddr));
        (void)memcpy(&itaddr, ea->arp_tpa, sizeof (itaddr));
        for (ia = in_ifaddrhead.tqh_first; ia; ia = ia->ia_link.tqe_next)
#if BRIDGE
                /*
                 * For a bridge, we want to check the address irrespective
                 * of the receive interface. (This will change slightly
                 * when we have clusters of interfaces).
                 */
                {
#else
                if (ia->ia_ifp == &ac->ac_if) {
#endif
                        maybe_ia = ia;
                        if ((itaddr.s_addr == ia->ia_addr.sin_addr.s_addr) ||
                             (isaddr.s_addr == ia->ia_addr.sin_addr.s_addr))
                                break;
                }
        if (maybe_ia == 0) {
                m_freem(m);
                return;
        }
        myaddr = ia ? ia->ia_addr.sin_addr : maybe_ia->ia_addr.sin_addr;

#if 0
        /*
         * In order to support BlueBox networking, we need to allow
         *   "self-addressed" stamped envelopes
         */
        if (!bcmp((caddr_t)ea->arp_sha, (caddr_t)ac->ac_enaddr,
            sizeof (ea->arp_sha))) {
                m_freem(m);     /* it's from me, ignore it. */
                return;
        }
#endif
        if (!bcmp((caddr_t)ea->arp_sha, (caddr_t)etherbroadcastaddr,
            sizeof (ea->arp_sha))) {
                log(LOG_ERR,
                    "arp: ether 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,
                   "duplicate IP address %s sent from ethernet address %s\n",
                   inet_ntoa(isaddr), ether_sprintf(buf, ea->arp_sha));
                itaddr = myaddr;
                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))) {
#ifndef BRIDGE /* the following is not an error when doing bridging */
                if (rt->rt_ifp != &ac->ac_if) {
                        log(LOG_ERR, "arp: %s is on %s%d but got reply from %6D on %s%d\n",
                            inet_ntoa(isaddr),
                            rt->rt_ifp->if_name, rt->rt_ifp->if_unit,
                            ea->arp_sha, ":",
                            ac->ac_if.if_name, ac->ac_if.if_unit);
                        goto reply;
                }
#endif
                if (sdl->sdl_alen &&
                    bcmp((caddr_t)ea->arp_sha, LLADDR(sdl), sdl->sdl_alen))
                        if (rt->rt_expire)
                            log(LOG_INFO, "arp: %s moved from %6D to %6D on %s%d\n",
                                inet_ntoa(isaddr), (u_char *)LLADDR(sdl), ":",
                                ea->arp_sha, ":",
                                ac->ac_if.if_name, ac->ac_if.if_unit);
                        else {
                            log(LOG_ERR,
                                "arp: %6D attempts to modify permanent entry for %s on %s%d",
                                ea->arp_sha, ":", inet_ntoa(isaddr),
                                ac->ac_if.if_name, ac->ac_if.if_unit);
                            goto reply;
                        }
                (void)memcpy(LLADDR(sdl), ea->arp_sha, sizeof(ea->arp_sha));
                sdl->sdl_alen = sizeof(ea->arp_sha);
                if (rt->rt_expire)
                        rt->rt_expire = time_second + arpt_keep;
                rt->rt_flags &= ~RTF_REJECT;
                la->la_asked = 0;
                if (la->la_hold) {
                        dlil_output((u_long) ac, la->la_hold, rt,
                                rt_key(rt), 0);
                        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(ea->arp_tha, ea->arp_sha, sizeof(ea->arp_sha));
                (void)memcpy(ea->arp_sha, ac->ac_enaddr, sizeof(ea->arp_sha));
        } 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 == &ac->ac_if) {
                                rtfree(rt);
                                m_freem(m);
                                return;
                        }
                        (void)memcpy(ea->arp_tha, ea->arp_sha, sizeof(ea->arp_sha));
                        (void)memcpy(ea->arp_sha, ac->ac_enaddr, sizeof(ea->arp_sha));
                        rtfree(rt);
#if DEBUG_PROXY
                        printf("arp: proxying for %s\n",
                               inet_ntoa(itaddr));
#endif
                } else {
                        rt = la->la_rt;
                        (void)memcpy(ea->arp_tha, ea->arp_sha, sizeof(ea->arp_sha));
                        sdl = SDL(rt->rt_gateway);
                        (void)memcpy(ea->arp_sha, LLADDR(sdl), sizeof(ea->arp_sha));
                }
        }

        (void)memcpy(ea->arp_tpa, ea->arp_spa, sizeof(ea->arp_spa));
        (void)memcpy(ea->arp_spa, &itaddr, sizeof(ea->arp_spa));
        ea->arp_op = htons(ARPOP_REPLY);
        ea->arp_pro = htons(ETHERTYPE_IP); /* let's be sure! */
        eh = (struct ether_header *)sa.sa_data;
        (void)memcpy(eh->ether_dhost, ea->arp_tha, sizeof(eh->ether_dhost));
        eh->ether_type = htons(ETHERTYPE_ARP);
        sa.sa_family = AF_UNSPEC;
        sa.sa_len = sizeof(sa);
        dlil_output((u_long) ac, m, 0, &sa, 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_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 && create) {
                log(LOG_DEBUG, "arplookup %s failed: %s\n",
                    inet_ntoa(sin.sin_addr), why);
                return 0;
        } else if (why) {
                return 0;
        }
        return ((struct llinfo_arp *)rt->rt_llinfo);
}

void
arp_ifinit(ac, ifa)
        struct arpcom *ac;
        struct ifaddr *ifa;
{
        if (ntohl(IA_SIN(ifa)->sin_addr.s_addr) != INADDR_ANY)
                arprequest(ac, &IA_SIN(ifa)->sin_addr,
                               &IA_SIN(ifa)->sin_addr, ac->ac_enaddr);
        ifa->ifa_rtrequest = arp_rtrequest;
        ifa->ifa_flags |= RTF_CLONING;
}