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

/*
 * Copyright (c) 2004-2009 Apple Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The 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, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * Copyright (c) 1982, 1989, 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.
 *
 */

#include <kern/debug.h>
#include <netinet/in_arp.h>
#include <sys/types.h>
#include <sys/param.h>
#include <sys/kernel_types.h>
#include <sys/syslog.h>
#include <sys/systm.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/mbuf.h>
#include <sys/sysctl.h>
#include <string.h>
#include <net/if_arp.h>
#include <net/if_dl.h>
#include <net/dlil.h>
#include <net/if_types.h>
#include <net/route.h>
#include <netinet/if_ether.h>
#include <netinet/in_var.h>
#include <kern/zalloc.h>

#define SA(p) ((struct sockaddr *)(p))
#define SIN(s) ((struct sockaddr_in *)s)
#define CONST_LLADDR(s) ((const u_char*)((s)->sdl_data + (s)->sdl_nlen))
#define rt_expire rt_rmx.rmx_expire
#define equal(a1, a2) (bcmp((caddr_t)(a1), (caddr_t)(a2), (a1)->sa_len) == 0)

static const size_t MAX_HW_LEN = 10;

SYSCTL_DECL(_net_link_ether);
SYSCTL_NODE(_net_link_ether, PF_INET, inet, CTLFLAG_RW|CTLFLAG_LOCKED, 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 */

/* Apple Hardware SUM16 checksuming */
int apple_hwcksum_tx = 1;
int apple_hwcksum_rx = 1;

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, "");
SYSCTL_INT(_net_link_ether_inet, OID_AUTO, apple_hwcksum_tx, CTLFLAG_RW,
           &apple_hwcksum_tx, 0, "");
SYSCTL_INT(_net_link_ether_inet, OID_AUTO, apple_hwcksum_rx, CTLFLAG_RW,
           &apple_hwcksum_rx, 0, "");

struct llinfo_arp {
        /*
         * The following are protected by rnh_lock
         */
        LIST_ENTRY(llinfo_arp) la_le;
        struct  rtentry *la_rt;
        /*
         * The following are protected by rt_lock
         */
        struct  mbuf *la_hold;          /* last packet until resolved/timeout */
        int32_t la_asked;               /* last time we QUERIED for this addr */
};

/*
 * Synchronization notes:
 *
 * The global list of ARP entries are stored in llinfo_arp; an entry
 * gets inserted into the list when the route is created and gets
 * removed from the list when it is deleted; this is done as part
 * of RTM_ADD/RTM_RESOLVE/RTM_DELETE in arp_rtrequest().
 *
 * Because rnh_lock and rt_lock for the entry are held during those
 * operations, the same locks (and thus lock ordering) must be used
 * elsewhere to access the relevant data structure fields:
 *
 * la_le.{le_next,le_prev}, la_rt
 *
 *      - Routing lock (rnh_lock)
 *
 * la_hold, la_asked
 *
 *      - Routing entry lock (rt_lock)
 *
 * Due to the dependency on rt_lock, llinfo_arp has the same lifetime
 * as the route entry itself.  When a route is deleted (RTM_DELETE),
 * it is simply removed from the global list but the memory is not
 * freed until the route itself is freed.
 */
static LIST_HEAD(, llinfo_arp) llinfo_arp;

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_sendllconflict = 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, "");
SYSCTL_INT(_net_link_ether_inet, OID_AUTO, sendllconflict, CTLFLAG_RW,
           &arp_sendllconflict, 0, "");

static int log_arp_warnings = 0;

SYSCTL_INT(_net_link_ether_inet, OID_AUTO, log_arp_warnings, CTLFLAG_RW,
        &log_arp_warnings, 0,
        "log arp warning messages");

static int keep_announcements = 1;
SYSCTL_INT(_net_link_ether_inet, OID_AUTO, keep_announcements, CTLFLAG_RW,
        &keep_announcements, 0,
        "keep arp announcements");

static int send_conflicting_probes = 1;
SYSCTL_INT(_net_link_ether_inet, OID_AUTO, send_conflicting_probes, CTLFLAG_RW,
        &send_conflicting_probes, 0,
        "send conflicting link-local arp probes");

static errno_t arp_lookup_route(const struct in_addr *, int,
    int, route_t *, unsigned int);
static void arptimer(void *);
static struct llinfo_arp *arp_llinfo_alloc(void);
static void arp_llinfo_free(void *);

extern u_int32_t        ipv4_ll_arp_aware;

static int arpinit_done;

static struct zone *llinfo_arp_zone;
#define LLINFO_ARP_ZONE_MAX     256             /* maximum elements in zone */
#define LLINFO_ARP_ZONE_NAME    "llinfo_arp"    /* name for zone */

void
arp_init(void)
{
        if (arpinit_done) {
                log(LOG_NOTICE, "arp_init called more than once (ignored)\n");
                return;
        }

        LIST_INIT(&llinfo_arp);

        llinfo_arp_zone = zinit(sizeof (struct llinfo_arp),
            LLINFO_ARP_ZONE_MAX * sizeof (struct llinfo_arp), 0,
            LLINFO_ARP_ZONE_NAME);
        if (llinfo_arp_zone == NULL)
                panic("%s: failed allocating llinfo_arp_zone", __func__);

        zone_change(llinfo_arp_zone, Z_EXPAND, TRUE);

        arpinit_done = 1;

        /* start timer */
        timeout(arptimer, (caddr_t)0, hz);
}

static struct llinfo_arp *
arp_llinfo_alloc(void)
{
        return (zalloc(llinfo_arp_zone));
}

static void
arp_llinfo_free(void *arg)
{
        struct llinfo_arp *la = arg;

        if (la->la_le.le_next != NULL || la->la_le.le_prev != NULL) {
                panic("%s: trying to free %p when it is in use", __func__, la);
                /* NOTREACHED */
        }

        /* Just in case there's anything there, free it */
        if (la->la_hold != NULL) {
                m_freem(la->la_hold);
                la->la_hold = NULL;
        }

        zfree(llinfo_arp_zone, la);
}

/*
 * Free an arp entry.
 */
static void
arptfree(struct llinfo_arp *la)
{
        struct rtentry *rt = la->la_rt;
        struct sockaddr_dl *sdl;

        lck_mtx_assert(rnh_lock, LCK_MTX_ASSERT_OWNED);
        RT_LOCK_ASSERT_HELD(rt);

        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;
                RT_UNLOCK(rt);
        } else {
                /*
                 * Safe to drop rt_lock and use rt_key, since holding
                 * rnh_lock here prevents another thread from calling
                 * rt_setgate() on this route.
                 */
                RT_UNLOCK(rt);
                rtrequest_locked(RTM_DELETE, rt_key(rt), NULL, rt_mask(rt),
                    0, NULL);
        }
}

/*
 * Timeout routine.  Age arp_tab entries periodically.
 */
/* ARGSUSED */
static void
arptimer(void *ignored_arg)
{
#pragma unused (ignored_arg)
        struct llinfo_arp *la, *ola;
        struct timeval timenow;

        lck_mtx_lock(rnh_lock);
        la = llinfo_arp.lh_first;
        getmicrotime(&timenow);
        while ((ola = la) != 0) {
                struct rtentry *rt = la->la_rt;
                la = la->la_le.le_next;
                RT_LOCK(rt);
                if (rt->rt_expire && rt->rt_expire <= timenow.tv_sec)
                        arptfree(ola); /* timer has expired, clear */
                else
                        RT_UNLOCK(rt);
        }
        lck_mtx_unlock(rnh_lock);
        timeout(arptimer, (caddr_t)0, arpt_prune * hz);
}

/*
 * Parallel to llc_rtrequest.
 */
static void
arp_rtrequest(
        int req,
        struct rtentry *rt,
        __unused struct sockaddr *sa)
{
        struct sockaddr *gate = rt->rt_gateway;
        struct llinfo_arp *la = rt->rt_llinfo;
        static struct sockaddr_dl null_sdl = {sizeof(null_sdl), AF_LINK, 0, 0, 0, 0, 0, {0}};
        struct timeval timenow;

        if (!arpinit_done) {
                panic("%s: ARP has not been initialized", __func__);
                /* NOTREACHED */
        }
        lck_mtx_assert(rnh_lock, LCK_MTX_ASSERT_OWNED);
        RT_LOCK_ASSERT_HELD(rt);

        if (rt->rt_flags & RTF_GATEWAY)
                return;
        getmicrotime(&timenow);
        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.
                         */
                        if (rt_setgate(rt, rt_key(rt),
                            (struct sockaddr *)&null_sdl) == 0) {
                                gate = rt->rt_gateway;
                                SDL(gate)->sdl_type = rt->rt_ifp->if_type;
                                SDL(gate)->sdl_index = rt->rt_ifp->if_index;
                                /*
                                 * In case we're called before 1.0 sec.
                                 * has elapsed.
                                 */
                                rt->rt_expire = MAX(timenow.tv_sec, 1);
                        }
                        break;
                }
                /* Announce a new entry if requested. */
                if (rt->rt_flags & RTF_ANNOUNCE) {
                        RT_UNLOCK(rt);
                        dlil_send_arp(rt->rt_ifp, ARPOP_REQUEST,
                            SDL(gate), rt_key(rt), NULL, rt_key(rt));
                        RT_LOCK(rt);
                }
                /*FALLTHROUGH*/
        case RTM_RESOLVE:
                if (gate->sa_family != AF_LINK ||
                    gate->sa_len < sizeof(null_sdl)) {
                        if (log_arp_warnings)
                                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.
                 */
                rt->rt_llinfo = la = arp_llinfo_alloc();
                if (la == NULL) {
                        if (log_arp_warnings)
                                log(LOG_DEBUG, "%s: malloc failed\n", __func__);
                        break;
                }
                rt->rt_llinfo_free = arp_llinfo_free;

                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);

                /*
                 * 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_UNLOCK(rt);
                        dlil_resolve_multi(rt->rt_ifp, rt_key(rt), gate,
                            sizeof(struct sockaddr_dl));
                        RT_LOCK(rt);
                        rt->rt_expire = 0;
                }
                else if (in_broadcast(SIN(rt_key(rt))->sin_addr, rt->rt_ifp)) {
                        struct sockaddr_dl      *gate_ll = SDL(gate);
                        size_t  broadcast_len;
                        ifnet_llbroadcast_copy_bytes(rt->rt_ifp,
                            LLADDR(gate_ll), sizeof(gate_ll->sdl_data),
                            &broadcast_len);
                        gate_ll->sdl_alen = broadcast_len;
                        gate_ll->sdl_family = AF_LINK;
                        gate_ll->sdl_len = sizeof(struct sockaddr_dl);
                        /* In case we're called before 1.0 sec. has elapsed */
                        rt->rt_expire = MAX(timenow.tv_sec, 1);
                }

                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;
                        ifnet_lladdr_copy_bytes(rt->rt_ifp, LLADDR(SDL(gate)), SDL(gate)->sdl_alen = 6);
                        if (useloopback)
                                rt->rt_ifp = lo_ifp;

                }
                break;

        case RTM_DELETE:
                if (la == 0)
                        break;
                arp_inuse--;
                /*
                 * Unchain it but defer the actual freeing until the route
                 * itself is to be freed.  rt->rt_llinfo still points to
                 * llinfo_arp, and likewise, la->la_rt still points to this
                 * route entry, except that RTF_LLINFO is now cleared.
                 */
                LIST_REMOVE(la, la_le);
                la->la_le.le_next = NULL;
                la->la_le.le_prev = NULL;
                rt->rt_flags &= ~RTF_LLINFO;
                if (la->la_hold != NULL)
                        m_freem(la->la_hold);
                la->la_hold = NULL;
        }
}

/*
 * convert hardware address to hex string for logging errors.
 */
static const char *
sdl_addr_to_hex(const struct sockaddr_dl *sdl, char * orig_buf, int buflen)
{
        char *          buf = orig_buf;
        int             i;
        const u_char *  lladdr = (u_char *)(size_t)sdl->sdl_data;
        int                     maxbytes = buflen / 3;
        
        if (maxbytes > sdl->sdl_alen) {
                maxbytes = sdl->sdl_alen;
        }       
        *buf = '\0';
        for (i = 0; i < maxbytes; i++) {
                snprintf(buf, 3, "%02x", lladdr[i]);
                buf += 2;
                *buf = (i == maxbytes - 1) ? '\0' : ':';
                buf++;
        }
        return (orig_buf);
}

/*
 * arp_lookup_route will lookup the route for a given address.
 *
 * The address must be for a host on a local network on this interface.
 * If the returned route is non-NULL, the route is locked and the caller
 * is responsible for unlocking it and releasing its reference.
 */
static errno_t
arp_lookup_route(const struct in_addr *addr, int create, int proxy,
    route_t *route, unsigned int ifscope)
{
        struct sockaddr_inarp sin = {sizeof(sin), AF_INET, 0, {0}, {0}, 0, 0};
        const char *why = NULL;
        errno_t error = 0;
        route_t rt;

        *route = NULL;

        sin.sin_addr.s_addr = addr->s_addr;
        sin.sin_other = proxy ? SIN_PROXY : 0;

        rt = rtalloc1_scoped((struct sockaddr*)&sin, create, 0, ifscope);
        if (rt == NULL)
                return (ENETUNREACH);

        RT_LOCK(rt);

        if (rt->rt_flags & RTF_GATEWAY) {
                why = "host is not on local network";
                error = ENETUNREACH;
        } else if (!(rt->rt_flags & RTF_LLINFO)) {
                why = "could not allocate llinfo";
                error = ENOMEM;
        } else if (rt->rt_gateway->sa_family != AF_LINK) {
                why = "gateway route is not ours";
                error = EPROTONOSUPPORT;
        }

        if (error != 0) {
                if (create && log_arp_warnings) {
                        char tmp[MAX_IPv4_STR_LEN];
                        log(LOG_DEBUG, "arplookup link#%d %s failed: %s\n",
                            ifscope, inet_ntop(AF_INET, addr, tmp,
                            sizeof (tmp)), why);
                }

                /*
                 * If there are no references to this route, and it is
                 * a cloned route, and not static, and ARP had created
                 * the route, then purge it from the routing table as
                 * it is probably bogus.
                 */
                if (rt->rt_refcnt == 1 &&
                    (rt->rt_flags & (RTF_WASCLONED | RTF_STATIC)) ==
                    RTF_WASCLONED) {
                        /*
                         * Prevent another thread from modiying rt_key,
                         * rt_gateway via rt_setgate() after rt_lock is
                         * dropped by marking the route as defunct.
                         */
                        rt->rt_flags |= RTF_CONDEMNED;
                        RT_UNLOCK(rt);
                        rtrequest(RTM_DELETE, rt_key(rt), rt->rt_gateway,
                            rt_mask(rt), rt->rt_flags, 0);
                        rtfree(rt);
                } else {
                        RT_REMREF_LOCKED(rt);
                        RT_UNLOCK(rt);
                }
                return (error);
        }

        /*
         * Caller releases reference and does RT_UNLOCK(rt).
         */
        *route = rt;
        return (0);
}

/*
 * arp_route_to_gateway_route will find the gateway route for a given route.
 *
 * If the route is down, look the route up again.
 * If the route goes through a gateway, get the route to the gateway.
 * If the gateway route is down, look it up again.
 * If the route is set to reject, verify it hasn't expired.
 *
 * If the returned route is non-NULL, the caller is responsible for
 * releasing the reference and unlocking the route.
 */
#define senderr(e) { error = (e); goto bad; }
__private_extern__ errno_t
arp_route_to_gateway_route(const struct sockaddr *net_dest, route_t hint0,
     route_t *out_route)
{
        struct timeval timenow;
        route_t rt = hint0, hint = hint0;
        errno_t error = 0;

        *out_route = NULL;

        /*
         * Next hop determination.  Because we may involve the gateway route
         * in addition to the original route, locking is rather complicated.
         * The general concept is that regardless of whether the route points
         * to the original route or to the gateway route, this routine takes
         * an extra reference on such a route.  This extra reference will be
         * released at the end.
         *
         * Care must be taken to ensure that the "hint0" route never gets freed
         * via rtfree(), since the caller may have stored it inside a struct
         * route with a reference held for that placeholder.
         */
        if (rt != NULL) {
                unsigned int ifindex;

                RT_LOCK_SPIN(rt);
                ifindex = rt->rt_ifp->if_index;
                RT_ADDREF_LOCKED(rt);
                if (!(rt->rt_flags & RTF_UP)) {
                        RT_REMREF_LOCKED(rt);
                        RT_UNLOCK(rt);
                        /* route is down, find a new one */
                        hint = rt = rtalloc1_scoped((struct sockaddr *)
                            (size_t)net_dest, 1, 0, ifindex);
                        if (hint != NULL) {
                                RT_LOCK_SPIN(rt);
                                ifindex = rt->rt_ifp->if_index;
                        } else {
                                senderr(EHOSTUNREACH);
                        }
                }

                /*
                 * We have a reference to "rt" by now; it will either
                 * be released or freed at the end of this routine.
                 */
                RT_LOCK_ASSERT_HELD(rt);
                if (rt->rt_flags & RTF_GATEWAY) {
                        struct rtentry *gwrt = rt->rt_gwroute;
                        struct sockaddr_in gw;

                        /* If there's no gateway rt, look it up */
                        if (gwrt == NULL) {
                                gw = *((struct sockaddr_in *)rt->rt_gateway);
                                RT_UNLOCK(rt);
                                goto lookup;
                        }
                        /* Become a regular mutex */
                        RT_CONVERT_LOCK(rt);

                        /*
                         * Take gwrt's lock while holding route's lock;
                         * this is okay since gwrt never points back
                         * to "rt", so no lock ordering issues.
                         */
                        RT_LOCK_SPIN(gwrt);
                        if (!(gwrt->rt_flags & RTF_UP)) {
                                struct rtentry *ogwrt;

                                rt->rt_gwroute = NULL;
                                RT_UNLOCK(gwrt);
                                gw = *((struct sockaddr_in *)rt->rt_gateway);
                                RT_UNLOCK(rt);
                                rtfree(gwrt);
lookup:
                                gwrt = rtalloc1_scoped(
                                    (struct sockaddr *)&gw, 1, 0, ifindex);

                                RT_LOCK(rt);
                                /*
                                 * Bail out if the route is down, no route
                                 * to gateway, circular route, or if the
                                 * gateway portion of "rt" has changed.
                                 */
                                if (!(rt->rt_flags & RTF_UP) ||
                                    gwrt == NULL || gwrt == rt ||
                                    !equal(SA(&gw), rt->rt_gateway)) {
                                        if (gwrt == rt) {
                                                RT_REMREF_LOCKED(gwrt);
                                                gwrt = NULL;
                                        }
                                        RT_UNLOCK(rt);
                                        if (gwrt != NULL)
                                                rtfree(gwrt);
                                        senderr(EHOSTUNREACH);
                                }

                                /* Remove any existing gwrt */
                                ogwrt = rt->rt_gwroute;
                                if ((rt->rt_gwroute = gwrt) != NULL)
                                        RT_ADDREF(gwrt);

                                /* Clean up "rt" now while we can */
                                if (rt == hint0) {
                                        RT_REMREF_LOCKED(rt);
                                        RT_UNLOCK(rt);
                                } else {
                                        RT_UNLOCK(rt);
                                        rtfree(rt);
                                }
                                rt = gwrt;
                                /* Now free the replaced gwrt */
                                if (ogwrt != NULL)
                                        rtfree(ogwrt);
                                /* If still no route to gateway, bail out */
                                if (rt == NULL)
                                        senderr(EHOSTUNREACH);
                        } else {
                                RT_ADDREF_LOCKED(gwrt);
                                RT_UNLOCK(gwrt);
                                /* Clean up "rt" now while we can */
                                if (rt == hint0) {
                                        RT_REMREF_LOCKED(rt);
                                        RT_UNLOCK(rt);
                                } else {
                                        RT_UNLOCK(rt);
                                        rtfree(rt);
                                }
                                rt = gwrt;
                        }

                        /* rt == gwrt; if it is now down, give up */
                        RT_LOCK_SPIN(rt);
                        if (!(rt->rt_flags & RTF_UP)) {
                                RT_UNLOCK(rt);
                                senderr(EHOSTUNREACH);
                        }
                }

                if (rt->rt_flags & RTF_REJECT) {
                        getmicrotime(&timenow);
                        if (rt->rt_rmx.rmx_expire == 0 ||
                            timenow.tv_sec < rt->rt_rmx.rmx_expire) {
                                RT_UNLOCK(rt);
                                senderr(rt == hint ? EHOSTDOWN : EHOSTUNREACH);
                        }
                }

                /* Become a regular mutex */
                RT_CONVERT_LOCK(rt);

                /* Caller is responsible for cleaning up "rt" */
                *out_route = rt;
        }
        return (0);

bad:
        /* Clean up route (either it is "rt" or "gwrt") */
        if (rt != NULL) {
                RT_LOCK_SPIN(rt);
                if (rt == hint0) {
                        RT_REMREF_LOCKED(rt);
                        RT_UNLOCK(rt);
                } else {
                        RT_UNLOCK(rt);
                        rtfree(rt);
                }
        }
        return (error);
}
#undef senderr

/*
 * This is the ARP pre-output routine; care must be taken to ensure that
 * the "hint" route never gets freed via rtfree(), since the caller may
 * have stored it inside a struct route with a reference held for that
 * placeholder.
 */
errno_t
arp_lookup_ip(ifnet_t ifp, const struct sockaddr_in *net_dest,
    struct sockaddr_dl *ll_dest, size_t ll_dest_len, route_t hint,
    mbuf_t packet)
{
        route_t route = NULL;   /* output route */
        errno_t result = 0;
        struct sockaddr_dl      *gateway;
        struct llinfo_arp       *llinfo;
        struct timeval timenow;

        if (net_dest->sin_family != AF_INET)
                return (EAFNOSUPPORT);

        if ((ifp->if_flags & (IFF_UP|IFF_RUNNING)) != (IFF_UP|IFF_RUNNING))
                return (ENETDOWN);

        /*
         * If we were given a route, verify the route and grab the gateway
         */
        if (hint != NULL) {
                /*
                 * Callee holds a reference on the route and returns
                 * with the route entry locked, upon success.
                 */
                result = arp_route_to_gateway_route((const struct sockaddr*)
                    net_dest, hint, &route);
                if (result != 0)
                        return (result);
                if (route != NULL)
                        RT_LOCK_ASSERT_HELD(route);
        }

        if (packet->m_flags & M_BCAST) {
                size_t  broadcast_len;
                bzero(ll_dest, ll_dest_len);
                result = ifnet_llbroadcast_copy_bytes(ifp, LLADDR(ll_dest),
                    ll_dest_len - offsetof(struct sockaddr_dl, sdl_data),
                    &broadcast_len);
                if (result == 0) {
                        ll_dest->sdl_alen = broadcast_len;
                        ll_dest->sdl_family = AF_LINK;
                        ll_dest->sdl_len = sizeof(struct sockaddr_dl);
                }
                goto release;
        }
        if (packet->m_flags & M_MCAST) {
                if (route != NULL)
                        RT_UNLOCK(route);
                result = dlil_resolve_multi(ifp,
                    (const struct sockaddr*)net_dest,
                    (struct sockaddr*)ll_dest, ll_dest_len);
                if (route != NULL)
                        RT_LOCK(route);
                goto release;
        }

        /*
         * If we didn't find a route, or the route doesn't have
         * link layer information, trigger the creation of the
         * route and link layer information.
         */
        if (route == NULL || route->rt_llinfo == NULL) {
                /* Clean up now while we can */
                if (route != NULL) {
                        if (route == hint) {
                                RT_REMREF_LOCKED(route);
                                RT_UNLOCK(route);
                        } else {
                                RT_UNLOCK(route);
                                rtfree(route);
                        }
                }
                /*
                 * Callee holds a reference on the route and returns
                 * with the route entry locked, upon success.
                 */
                result = arp_lookup_route(&net_dest->sin_addr, 1, 0, &route,
                    ifp->if_index);
                if (result == 0)
                        RT_LOCK_ASSERT_HELD(route);
        }

        if (result || route == NULL || route->rt_llinfo == NULL) {
                char    tmp[MAX_IPv4_STR_LEN];

                /* In case result is 0 but no route, return an error */
                if (result == 0)
                        result = EHOSTUNREACH;

                if (log_arp_warnings &&
                    route != NULL && route->rt_llinfo == NULL)
                        log(LOG_DEBUG, "arpresolve: can't allocate llinfo "
                            "for %s\n", inet_ntop(AF_INET, &net_dest->sin_addr,
                            tmp, sizeof(tmp)));
                goto release;
        }

        /*
         * Now that we have the right route, is it filled in?
         */
        gateway = SDL(route->rt_gateway);
        getmicrotime(&timenow);
        if ((route->rt_rmx.rmx_expire == 0 ||
            route->rt_rmx.rmx_expire > timenow.tv_sec) && gateway != NULL &&
            gateway->sdl_family == AF_LINK && gateway->sdl_alen != 0) {
                bcopy(gateway, ll_dest, MIN(gateway->sdl_len, ll_dest_len));
                result = 0;
                goto release;
        }

        if (ifp->if_flags & IFF_NOARP) {
                result = ENOTSUP;
                goto release;
        }

        /*
         * Route wasn't complete/valid. We need to arp.
         */
        llinfo = route->rt_llinfo;
        if (packet != NULL) {
                if (llinfo->la_hold != NULL)
                        m_freem(llinfo->la_hold);
                llinfo->la_hold = packet;
        }

        if (route->rt_rmx.rmx_expire) {
                route->rt_flags &= ~RTF_REJECT;
                if (llinfo->la_asked == 0 ||
                    route->rt_rmx.rmx_expire != timenow.tv_sec) {
                        route->rt_rmx.rmx_expire = timenow.tv_sec;
                        if (llinfo->la_asked++ < arp_maxtries) {
                                struct ifaddr *rt_ifa = route->rt_ifa;
                                ifaref(rt_ifa);
                                RT_UNLOCK(route);
                                dlil_send_arp(ifp, ARPOP_REQUEST, NULL,
                                    rt_ifa->ifa_addr, NULL,
                                    (const struct sockaddr*)net_dest);
                                ifafree(rt_ifa);
                                RT_LOCK(route);
                                result = EJUSTRETURN;
                                goto release;
                        } else {
                                route->rt_flags |= RTF_REJECT;
                                route->rt_rmx.rmx_expire += arpt_down;
                                llinfo->la_asked = 0;
                                llinfo->la_hold = NULL;
                                result = EHOSTUNREACH;
                                goto release;
                        }
                }
        }

        /* The packet is now held inside la_hold (can "packet" be NULL?) */
        result = EJUSTRETURN;

release:
        if (route != NULL) {
                if (route == hint) {
                        RT_REMREF_LOCKED(route);
                        RT_UNLOCK(route);
                } else {
                        RT_UNLOCK(route);
                        rtfree(route);
                }
        }
        return (result);
}

errno_t
arp_ip_handle_input(
        ifnet_t         ifp,
        u_short         arpop,
        const struct sockaddr_dl *sender_hw,
        const struct sockaddr_in *sender_ip,
        const struct sockaddr_in *target_ip)
{
        char    ipv4str[MAX_IPv4_STR_LEN];
        struct sockaddr_dl proxied;
        struct sockaddr_dl *gateway, *target_hw = NULL;
        struct ifaddr *ifa;
        struct in_ifaddr *ia;
        struct in_ifaddr *best_ia = NULL;
        route_t route = NULL;
        char buf[3 * MAX_HW_LEN]; // enough for MAX_HW_LEN byte hw address
        struct llinfo_arp *llinfo;
        errno_t error;
        int created_announcement = 0;
        int bridged = 0, is_bridge = 0;
        
        /* Do not respond to requests for 0.0.0.0 */
        if (target_ip->sin_addr.s_addr == 0 && arpop == ARPOP_REQUEST)
                goto done;
        
        if (ifp->if_bridge)
                bridged = 1;
        if (ifp->if_type == IFT_BRIDGE)
                is_bridge = 1;

        /*
         * Determine if this ARP is for us
         * For a bridge, we want to check the address irrespective 
         * of the receive interface.
         */
        lck_rw_lock_shared(in_ifaddr_rwlock);
        TAILQ_FOREACH(ia, INADDR_HASH(target_ip->sin_addr.s_addr), ia_hash) {
                if (((bridged && ia->ia_ifp->if_bridge != NULL) ||
                        (ia->ia_ifp == ifp)) &&
                    ia->ia_addr.sin_addr.s_addr == target_ip->sin_addr.s_addr) {
                                best_ia = ia;
                                ifaref(&best_ia->ia_ifa);
                                lck_rw_done(in_ifaddr_rwlock);
                                goto match;
                }
        }

        TAILQ_FOREACH(ia, INADDR_HASH(sender_ip->sin_addr.s_addr), ia_hash) {
                if (((bridged && ia->ia_ifp->if_bridge != NULL) ||
                        (ia->ia_ifp == ifp)) &&
                    ia->ia_addr.sin_addr.s_addr == sender_ip->sin_addr.s_addr) {
                                best_ia = ia;
                                ifaref(&best_ia->ia_ifa);
                                lck_rw_done(in_ifaddr_rwlock);
                                goto match;
                }
        }

#define BDG_MEMBER_MATCHES_ARP(addr, ifp, ia)                                                           \
        (ia->ia_ifp->if_bridge == ifp->if_softc &&                                                              \
        !bcmp(ifnet_lladdr(ia->ia_ifp), ifnet_lladdr(ifp), ifp->if_addrlen) &&  \
        addr == ia->ia_addr.sin_addr.s_addr)
        /*
         * Check the case when bridge shares its MAC address with
         * some of its children, so packets are claimed by bridge
         * itself (bridge_input() does it first), but they are really
         * meant to be destined to the bridge member.
         */
        if (is_bridge) {
                TAILQ_FOREACH(ia, INADDR_HASH(target_ip->sin_addr.s_addr), ia_hash) {
                        if (BDG_MEMBER_MATCHES_ARP(target_ip->sin_addr.s_addr, ifp, ia)) {
                                ifp = ia->ia_ifp;
                                best_ia = ia;
                                ifaref(&best_ia->ia_ifa);
                                lck_rw_done(in_ifaddr_rwlock);
                                goto match;
                        }
                }
        }
        lck_rw_done(in_ifaddr_rwlock);

        /*
         * No match, use the first inet address on the receive interface
         * as a dummy address for the rest of the function; we may be
         * proxying for another address.
         */
        ifnet_lock_shared(ifp);
        TAILQ_FOREACH(ifa, &ifp->if_addrhead, ifa_link) {
                if (ifa->ifa_addr->sa_family != AF_INET)
                        continue;
                best_ia = (struct in_ifaddr *)ifa;
                ifaref(&best_ia->ia_ifa);
                ifnet_lock_done(ifp);
                goto match;
        }
        ifnet_lock_done(ifp);

        /*
         * If we're not a bridge member, or if we are but there's no
         * IPv4 address to use for the interface, drop the packet.
         */
        if (!bridged || best_ia == NULL)
                goto done;

match:
        /* If the packet is from this interface, ignore the packet */
        if (!bcmp(CONST_LLADDR(sender_hw), ifnet_lladdr(ifp), sender_hw->sdl_len)) {
                goto done;
        }

        /* Check for a conflict */
        if (!bridged && sender_ip->sin_addr.s_addr == best_ia->ia_addr.sin_addr.s_addr) {
                struct kev_msg        ev_msg;
                struct kev_in_collision *in_collision;
                u_char  storage[sizeof(struct kev_in_collision) + MAX_HW_LEN];
                in_collision = (struct kev_in_collision*)storage;
                log(LOG_ERR, "%s%d duplicate IP address %s sent from address %s\n",
                        ifp->if_name, ifp->if_unit,
                        inet_ntop(AF_INET, &sender_ip->sin_addr, ipv4str, sizeof(ipv4str)),
                        sdl_addr_to_hex(sender_hw, buf, sizeof(buf)));

                /* Send a kernel event so anyone can learn of the conflict */
                in_collision->link_data.if_family = ifp->if_family;
                in_collision->link_data.if_unit = ifp->if_unit;
                strncpy(&in_collision->link_data.if_name[0], ifp->if_name, IFNAMSIZ);
                in_collision->ia_ipaddr = sender_ip->sin_addr;
                in_collision->hw_len = sender_hw->sdl_alen < MAX_HW_LEN ? sender_hw->sdl_alen : MAX_HW_LEN;
                bcopy(CONST_LLADDR(sender_hw), (caddr_t)in_collision->hw_addr, in_collision->hw_len);
                ev_msg.vendor_code = KEV_VENDOR_APPLE;
                ev_msg.kev_class = KEV_NETWORK_CLASS;
                ev_msg.kev_subclass = KEV_INET_SUBCLASS;
                ev_msg.event_code = KEV_INET_ARPCOLLISION;
                ev_msg.dv[0].data_ptr = in_collision;
                ev_msg.dv[0].data_length = sizeof(struct kev_in_collision) + in_collision->hw_len;
                ev_msg.dv[1].data_length = 0;
                kev_post_msg(&ev_msg);

                goto respond;
        }

        /*
         * Look up the routing entry. If it doesn't exist and we are the
         * target, and the sender isn't 0.0.0.0, go ahead and create one.
         * Callee holds a reference on the route and returns with the route
         * entry locked, upon success.
         */
        error = arp_lookup_route(&sender_ip->sin_addr,
            (target_ip->sin_addr.s_addr == best_ia->ia_addr.sin_addr.s_addr &&
            sender_ip->sin_addr.s_addr != 0), 0, &route, ifp->if_index);

        if (error == 0)
                RT_LOCK_ASSERT_HELD(route);

        if (error || route == 0 || route->rt_gateway == 0) {
                if (arpop != ARPOP_REQUEST) {
                        goto respond;
                }
                if (arp_sendllconflict
                    && send_conflicting_probes != 0
                    && (ifp->if_eflags & IFEF_ARPLL) != 0 
                    && IN_LINKLOCAL(ntohl(target_ip->sin_addr.s_addr))
                    && sender_ip->sin_addr.s_addr == 0) {
                        /*
                         * Verify this ARP probe doesn't conflict with an IPv4LL we know of
                         * on another interface.
                         */
                        if (route != NULL) {
                                RT_REMREF_LOCKED(route);
                                RT_UNLOCK(route);
                                route = NULL;
                        }
                        /*
                         * Callee holds a reference on the route and returns
                         * with the route entry locked, upon success.
                         */
                        error = arp_lookup_route(&target_ip->sin_addr, 0, 0,
                            &route, ifp->if_index);

                        if (error == 0)
                                RT_LOCK_ASSERT_HELD(route);

                        if (error == 0 && route && route->rt_gateway) {
                                gateway = SDL(route->rt_gateway);
                                if (route->rt_ifp != ifp && gateway->sdl_alen != 0 
                                    && (gateway->sdl_alen != sender_hw->sdl_alen 
                                        || bcmp(CONST_LLADDR(gateway), CONST_LLADDR(sender_hw),
                                                gateway->sdl_alen) != 0)) {
                                        /*
                                         * A node is probing for an IPv4LL we know exists on a
                                         * different interface. We respond with a conflicting probe
                                         * to force the new device to pick a different IPv4LL
                                         * address.
                                         */
                                        if (log_arp_warnings) {
                                            log(LOG_INFO,
                                                "arp: %s on %s%d sent probe for %s, already on %s%d\n",
                                                sdl_addr_to_hex(sender_hw, buf, sizeof(buf)),
                                                ifp->if_name, ifp->if_unit,
                                                inet_ntop(AF_INET, &target_ip->sin_addr, ipv4str,
                                                                  sizeof(ipv4str)),
                                                route->rt_ifp->if_name, route->rt_ifp->if_unit);
                                            log(LOG_INFO,
                                                "arp: sending conflicting probe to %s on %s%d\n",
                                                sdl_addr_to_hex(sender_hw, buf, sizeof(buf)),
                                                ifp->if_name, ifp->if_unit);
                                        }
                                        /* We're done with the route */
                                        RT_REMREF_LOCKED(route);
                                        RT_UNLOCK(route);
                                        route = NULL;
                                        /*
                                         * Send a conservative unicast "ARP probe".
                                         * This should force the other device to pick a new number.
                                         * This will not force the device to pick a new number if the device
                                         * has already assigned that number.
                                         * This will not imply to the device that we own that address.
                                         */
                                        ifnet_lock_shared(ifp);
                                        ifa = TAILQ_FIRST(&ifp->if_addrhead);
                                        if (ifa != NULL)
                                                ifaref(ifa);
                                        ifnet_lock_done(ifp);
                                        dlil_send_arp_internal(ifp, ARPOP_REQUEST,
                                                ifa != NULL ? SDL(ifa->ifa_addr) : NULL,
                                                (const struct sockaddr*)sender_ip, sender_hw,
                                                (const struct sockaddr*)target_ip);
                                        if (ifa != NULL) {
                                                ifafree(ifa);
                                                ifa = NULL;
                                        }
                                }
                        }
                        goto respond;
                } else if (keep_announcements != 0
                           && target_ip->sin_addr.s_addr == sender_ip->sin_addr.s_addr) {
                        /* don't create entry if link-local address and link-local is disabled */
                        if (!IN_LINKLOCAL(ntohl(sender_ip->sin_addr.s_addr)) 
                            || (ifp->if_eflags & IFEF_ARPLL) != 0) {
                                if (route != NULL) {
                                        RT_REMREF_LOCKED(route);
                                        RT_UNLOCK(route);
                                        route = NULL;
                                }
                                /*
                                 * Callee holds a reference on the route and
                                 * returns with the route entry locked, upon
                                 * success.
                                 */
                                error = arp_lookup_route(&sender_ip->sin_addr,
                                    1, 0, &route, ifp->if_index);

                                if (error == 0)
                                        RT_LOCK_ASSERT_HELD(route);

                                if (error == 0 && route != NULL && route->rt_gateway != NULL) {
                                        created_announcement = 1;
                                }
                        }
                        if (created_announcement == 0) {
                                goto respond;
                        }
                } else {
                        goto respond;
                }
        }

        RT_LOCK_ASSERT_HELD(route);
        gateway = SDL(route->rt_gateway);
        if (!bridged && route->rt_ifp != ifp) {
                if (!IN_LINKLOCAL(ntohl(sender_ip->sin_addr.s_addr)) || (ifp->if_eflags & IFEF_ARPLL) == 0) {
                        if (log_arp_warnings)
                                log(LOG_ERR, "arp: %s is on %s%d but got reply from %s on %s%d\n",
                                        inet_ntop(AF_INET, &sender_ip->sin_addr, ipv4str,
                                                          sizeof(ipv4str)),
                                        route->rt_ifp->if_name,
                                        route->rt_ifp->if_unit,
                                        sdl_addr_to_hex(sender_hw, buf, sizeof(buf)),
                                        ifp->if_name, ifp->if_unit);
                        goto respond;
                }
                else {
                        /* Don't change a permanent address */
                        if (route->rt_rmx.rmx_expire == 0) {
                                goto respond;
                        }

                        /*
                         * We're about to check and/or change the route's ifp
                         * and ifa, so do the lock dance: drop rt_lock, hold
                         * rnh_lock and re-hold rt_lock to avoid violating the
                         * lock ordering.  We have an extra reference on the
                         * route, so it won't go away while we do this.
                         */
                        RT_UNLOCK(route);
                        lck_mtx_lock(rnh_lock);
                        RT_LOCK(route);
                        /*
                         * Don't change the cloned route away from the
                         * parent's interface if the address did resolve
                         * or if the route is defunct.  rt_ifp on both
                         * the parent and the clone can now be freely
                         * accessed now that we have acquired rnh_lock.
                         */
                        gateway = SDL(route->rt_gateway);
                        if ((gateway->sdl_alen != 0 && route->rt_parent &&
                            route->rt_parent->rt_ifp == route->rt_ifp) ||
                            (route->rt_flags & RTF_CONDEMNED)) {
                                RT_REMREF_LOCKED(route);
                                RT_UNLOCK(route);
                                route = NULL;
                                lck_mtx_unlock(rnh_lock);
                                goto respond;
                        }
                        /* Change the interface when the existing route is on */
                        route->rt_ifp = ifp;
                        rtsetifa(route, &best_ia->ia_ifa);
                        gateway->sdl_index = ifp->if_index;
                        RT_UNLOCK(route);
                        lck_mtx_unlock(rnh_lock);
                        RT_LOCK(route);
                        /* Don't bother if the route is down */
                        if (!(route->rt_flags & RTF_UP))
                                goto respond;
                        /* Refresh gateway pointer */
                        gateway = SDL(route->rt_gateway);
                }
                RT_LOCK_ASSERT_HELD(route);
        }

        if (gateway->sdl_alen && bcmp(LLADDR(gateway), CONST_LLADDR(sender_hw), gateway->sdl_alen)) {
                if (route->rt_rmx.rmx_expire && log_arp_warnings) {
                        char buf2[3 * MAX_HW_LEN];
                        log(LOG_INFO, "arp: %s moved from %s to %s on %s%d\n",
                            inet_ntop(AF_INET, &sender_ip->sin_addr, ipv4str,
                            sizeof(ipv4str)),
                            sdl_addr_to_hex(gateway, buf, sizeof(buf)),
                            sdl_addr_to_hex(sender_hw, buf2, sizeof(buf2)),
                            ifp->if_name, ifp->if_unit);
                }
                else if (route->rt_rmx.rmx_expire == 0) {
                        if (log_arp_warnings) {
                                log(LOG_ERR, "arp: %s attempts to modify "
                                    "permanent entry for %s on %s%d\n",
                                    sdl_addr_to_hex(sender_hw, buf,
                                    sizeof(buf)),
                                    inet_ntop(AF_INET, &sender_ip->sin_addr,
                                    ipv4str, sizeof(ipv4str)),
                                    ifp->if_name, ifp->if_unit);
                        }
                        goto respond;
                }
        }

        /* Copy the sender hardware address in to the route's gateway address */
        gateway->sdl_alen = sender_hw->sdl_alen;
        bcopy(CONST_LLADDR(sender_hw), LLADDR(gateway), gateway->sdl_alen);

        /* Update the expire time for the route and clear the reject flag */
        if (route->rt_rmx.rmx_expire) {
                struct timeval timenow;

                getmicrotime(&timenow);
                route->rt_rmx.rmx_expire = timenow.tv_sec + arpt_keep;
        }
        route->rt_flags &= ~RTF_REJECT;

        /* update the llinfo, send a queued packet if there is one */
        llinfo = route->rt_llinfo;
        llinfo->la_asked = 0;
        if (llinfo->la_hold) {
                struct mbuf *m0;
                m0 = llinfo->la_hold;
                llinfo->la_hold = 0;

                RT_UNLOCK(route);
                dlil_output(ifp, PF_INET, m0, (caddr_t)route, rt_key(route), 0);
                RT_REMREF(route);
                route = NULL;
        }

respond:
        if (route != NULL) {
                RT_REMREF_LOCKED(route);
                RT_UNLOCK(route);
                route = NULL;
        }

        if (arpop != ARPOP_REQUEST)
                goto done;

        /* If we are not the target, check if we should proxy */
        if (target_ip->sin_addr.s_addr != best_ia->ia_addr.sin_addr.s_addr) {
                /*
                 * Find a proxy route; callee holds a reference on the
                 * route and returns with the route entry locked, upon
                 * success.
                 */
                error = arp_lookup_route(&target_ip->sin_addr, 0, SIN_PROXY,
                    &route, ifp->if_index);

                if (error == 0) {
                        RT_LOCK_ASSERT_HELD(route);
                        /*
                         * Return proxied ARP replies only on the interface
                         * or bridge cluster where this network resides.
                         * Otherwise we may conflict with the host we are
                         * proxying for.
                         */
                        if (route->rt_ifp != ifp &&
                                (route->rt_ifp->if_bridge != ifp->if_bridge ||
                                 ifp->if_bridge == NULL)) {
                                        RT_REMREF_LOCKED(route);
                                        RT_UNLOCK(route);
                                        goto done;
                                }
                        proxied = *SDL(route->rt_gateway);
                        target_hw = &proxied;
                } else {
                        /*
                         * We don't have a route entry indicating we should
                         * use proxy.  If we aren't supposed to proxy all,
                         * we are done.
                         */
                        if (!arp_proxyall)
                                goto done;

                        /*
                         * See if we have a route to the target ip before
                         * we proxy it.
                         */
                        route = rtalloc1_scoped((struct sockaddr *)
                            (size_t)target_ip, 0, 0, ifp->if_index);
                        if (!route)
                                goto done;

                        /*
                         * Don't proxy for hosts already on the same interface.
                         */
                        RT_LOCK(route);
                        if (route->rt_ifp == ifp) {
                                RT_UNLOCK(route);
                                rtfree(route);
                                goto done;
                        }
                }
                RT_REMREF_LOCKED(route);
                RT_UNLOCK(route);
        }

        dlil_send_arp(ifp, ARPOP_REPLY,
            target_hw, (const struct sockaddr*)target_ip,
            sender_hw, (const struct sockaddr*)sender_ip);

done:
        if (best_ia != NULL)
                ifafree(&best_ia->ia_ifa);
        return 0;
}

void
arp_ifinit(
        struct ifnet *ifp,
        struct ifaddr *ifa)
{
        ifa->ifa_rtrequest = arp_rtrequest;
        ifa->ifa_flags |= RTF_CLONING;
        dlil_send_arp(ifp, ARPOP_REQUEST, NULL, ifa->ifa_addr, NULL, ifa->ifa_addr);
}