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

/*
 * Copyright (c) 2004-2007 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/route.h>
#include <netinet/if_ether.h>
#include <netinet/in_var.h>

#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

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 {
        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 */
};

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");

extern u_int32_t        ipv4_ll_arp_aware;

/*
 * Free an arp entry.
 */
static void
arptfree(
        struct llinfo_arp *la)
{
        struct rtentry *rt = la->la_rt;
        struct sockaddr_dl *sdl;
        lck_mtx_assert(rt_mtx, LCK_MTX_ASSERT_OWNED);
        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_locked(RTM_DELETE, rt_key(rt), (struct sockaddr *)0, rt_mask(rt),
                        0, (struct rtentry **)0);
}

/*
 * 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(rt_mtx);
        la = llinfo_arp.lh_first;
        getmicrotime(&timenow);
        while ((ola = la) != 0) {
                struct rtentry *rt = la->la_rt;
                la = la->la_le.le_next;
                if (rt->rt_expire && rt->rt_expire <= timenow.tv_sec)
                        arptfree(ola); /* timer has expired, clear */
        }
        lck_mtx_unlock(rt_mtx);
        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 = (struct llinfo_arp *)rt->rt_llinfo;
        static struct sockaddr_dl null_sdl = {sizeof(null_sdl), AF_LINK, 0, 0, 0, 0, 0, {0}};
        static int arpinit_done;
        struct timeval timenow;

        if (!arpinit_done) {
                arpinit_done = 1;
                LIST_INIT(&llinfo_arp);
                timeout(arptimer, (caddr_t)0, hz);
        }
        lck_mtx_assert(rt_mtx, LCK_MTX_ASSERT_OWNED);

        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.
                         */
                        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;
                        /* 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)
                        dlil_send_arp(rt->rt_ifp, ARPOP_REQUEST, SDL(gate), rt_key(rt), (struct sockaddr_dl *)rt_key(rt), NULL);
                /*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.
                 */
                R_Malloc(la, struct llinfo_arp *, sizeof(*la));
                rt->rt_llinfo = (caddr_t)la;
                if (la == 0) {
                        if ( log_arp_warnings) 
                                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))) {
                        dlil_resolve_multi(rt->rt_ifp, rt_key(rt), gate, sizeof(struct sockaddr_dl));
                        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);
                }
#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;
                        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--;
                LIST_REMOVE(la, la_le);
                rt->rt_llinfo = NULL;
                rt->rt_flags &= ~RTF_LLINFO;
                if (la->la_hold) {
                        m_freem(la->la_hold);
                }
                la->la_hold = NULL;
                R_Free((caddr_t)la);
        }
}

/*
 * 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 *)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 routing lock must be held. The address must be for a
 * host on a local network on this interface.
 */
static errno_t
arp_lookup_route(
        const struct in_addr *addr,
        int     create,
        int proxy,
        route_t *route)
{
        struct sockaddr_inarp sin = {sizeof(sin), AF_INET, 0, {0}, {0}, 0, 0};
        const char *why = NULL;
        errno_t error = 0;
        
        // Caller is responsible for taking the routing lock
        lck_mtx_assert(rt_mtx, LCK_MTX_ASSERT_OWNED);

        sin.sin_addr.s_addr = addr->s_addr;
        sin.sin_other = proxy ? SIN_PROXY : 0;
        
        *route = rtalloc1_locked((struct sockaddr*)&sin, create, 0);
        if (*route == NULL)
                return ENETUNREACH;
        
        rtunref(*route);
        
        if ((*route)->rt_flags & RTF_GATEWAY) {
                why = "host is not on local network";
                
                /* If there are no references to this route, purge it */
                if ((*route)->rt_refcnt <= 0 && ((*route)->rt_flags & RTF_WASCLONED) != 0) {
                        rtrequest_locked(RTM_DELETE,
                                        (struct sockaddr *)rt_key(*route),
                                        (*route)->rt_gateway, rt_mask(*route),
                                        (*route)->rt_flags, 0);
                }
                *route = NULL;
                error = ENETUNREACH;
        }
        else if (((*route)->rt_flags & RTF_LLINFO) == 0) {
                why = "could not allocate llinfo";
                *route = NULL;
                error = ENOMEM;
        }
        else if ((*route)->rt_gateway->sa_family != AF_LINK) {
                why = "gateway route is not ours";
                *route = NULL;
                error = EPROTONOSUPPORT;
        }
        
        if (why && create && log_arp_warnings) {
                char    tmp[MAX_IPv4_STR_LEN];
                log(LOG_DEBUG, "arplookup %s failed: %s\n",
                        inet_ntop(AF_INET, addr, tmp, sizeof(tmp)), why);
        }
        
        return error;
}


__private_extern__ errno_t
arp_route_to_gateway_route(
        const struct sockaddr *net_dest,
        route_t hint,
        route_t *out_route);
/*
 * 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.
 */
__private_extern__ errno_t
arp_route_to_gateway_route(
        const struct sockaddr *net_dest,
        route_t hint,
        route_t *out_route)
{
        struct timeval timenow;
        route_t route = hint;
        *out_route = NULL;
        
        /* If we got a hint from the higher layers, check it out */
        if (route) {
                lck_mtx_lock(rt_mtx);
                
                if ((route->rt_flags & RTF_UP) == 0) {
                        /* route is down, find a new one */
                        hint = route = rtalloc1_locked(net_dest, 1, 0);
                        if (hint) {
                                rtunref(hint);
                        }
                        else {
                                /* No route to host */
                                lck_mtx_unlock(rt_mtx);
                                return EHOSTUNREACH;
                        }
                }
                
                if (route->rt_flags & RTF_GATEWAY) {
                        /*
                         * We need the gateway route. If it is NULL or down,
                         * look it up.
                         */
                        if (route->rt_gwroute == 0 ||
                                (route->rt_gwroute->rt_flags & RTF_UP) == 0) {
                                if (route->rt_gwroute != 0)
                                        rtfree_locked(route->rt_gwroute);
                                
                                route->rt_gwroute = rtalloc1_locked(route->rt_gateway, 1, 0);
                                if (route->rt_gwroute == 0) {
                                        lck_mtx_unlock(rt_mtx);
                                        return EHOSTUNREACH;
                                }
                        }
                        
                        route = route->rt_gwroute;
                }
                
                if (route->rt_flags & RTF_REJECT) {
                        getmicrotime(&timenow);
                        if (route->rt_rmx.rmx_expire == 0 ||
                                timenow.tv_sec < route->rt_rmx.rmx_expire) {
                                lck_mtx_unlock(rt_mtx);
                                return route == hint ? EHOSTDOWN : EHOSTUNREACH;
                        }
                }
                
                lck_mtx_unlock(rt_mtx);
        }
        
        *out_route = route;
        return 0;
}

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;
        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) {
                result = arp_route_to_gateway_route((const struct sockaddr*)net_dest,
                                                                                        hint, &route);
                if (result != 0)
                        return result;
        }
        
        if (packet->m_flags & M_BCAST) {
                u_long  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) {
                        return result;
                }
                
                ll_dest->sdl_alen = broadcast_len;
                ll_dest->sdl_family = AF_LINK;
                ll_dest->sdl_len = sizeof(struct sockaddr_dl);
                
                return 0;
        }
        if (packet->m_flags & M_MCAST) {
                return dlil_resolve_multi(ifp, (const struct sockaddr*)net_dest,
                                                                   (struct sockaddr*)ll_dest, ll_dest_len);
        }
        
        lck_mtx_lock(rt_mtx);
        
        /*
         * 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)
                result = arp_lookup_route(&net_dest->sin_addr, 1, 0, &route);
        
        if (result || route == NULL || route->rt_llinfo == NULL) {
                char    tmp[MAX_IPv4_STR_LEN];
                lck_mtx_unlock(rt_mtx);
                if (log_arp_warnings)
                        log(LOG_DEBUG, "arpresolve: can't allocate llinfo for %s\n",
                                inet_ntop(AF_INET, &net_dest->sin_addr, tmp, sizeof(tmp)));
                return result;
        }
        
        /*
         * 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));
                lck_mtx_unlock(rt_mtx);
                return 0;
        }
        
        /*
         * Route wasn't complete/valid. We need to arp.
         */
        if (ifp->if_flags & IFF_NOARP) {
                lck_mtx_unlock(rt_mtx);
                return ENOTSUP;
        }
        
        llinfo = (struct llinfo_arp*)route->rt_llinfo;
        if (packet) {
                if (llinfo->la_hold) {
                        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) {
                                lck_mtx_unlock(rt_mtx);
                                dlil_send_arp(ifp, ARPOP_REQUEST, NULL, route->rt_ifa->ifa_addr,
                                                          NULL, (const struct sockaddr*)net_dest);
                                return EJUSTRETURN;
                        }
                        else {
                                route->rt_flags |= RTF_REJECT;
                                route->rt_rmx.rmx_expire += arpt_down;
                                llinfo->la_asked = 0;
                                llinfo->la_hold = NULL;
                                lck_mtx_unlock(rt_mtx);
                                return EHOSTUNREACH;
                        }
                }
        }
        lck_mtx_unlock(rt_mtx);
        
        return EJUSTRETURN;
}

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 *gateway;
        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;
        
        /* Do not respond to requests for 0.0.0.0 */
        if (target_ip->sin_addr.s_addr == 0 && arpop == ARPOP_REQUEST) {
                return 0;
        }
        
        /*
         * Determine if this ARP is for us
         */
        lck_mtx_lock(rt_mtx);
        for (ia = in_ifaddrhead.tqh_first; ia; ia = ia->ia_link.tqe_next) {
                /* do_bridge should be tested here for bridging */
                if (ia->ia_ifp == ifp) {
                        best_ia = ia;
                        if (target_ip->sin_addr.s_addr == ia->ia_addr.sin_addr.s_addr ||
                                sender_ip->sin_addr.s_addr == ia->ia_addr.sin_addr.s_addr) {
                                break;
                        }
                }
        }
        
        /* If we don't have an IP address on this interface, ignore the packet */
        if (best_ia == 0) {
                lck_mtx_unlock(rt_mtx);
                return 0;
        }
        
        /* If the packet is from this interface, ignore the packet */
        if (!bcmp(CONST_LLADDR(sender_hw), ifnet_lladdr(ifp), sender_hw->sdl_len)) {
                lck_mtx_unlock(rt_mtx);
                return 0;
        }
        
        /* Check for a conflict */
        if (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, go ahead and create one.
         */
        error = arp_lookup_route(&sender_ip->sin_addr, (target_ip->sin_addr.s_addr ==
                                best_ia->ia_addr.sin_addr.s_addr), 0, &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.
                         */
                        error = arp_lookup_route(&target_ip->sin_addr, 0, 0, &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);
                                        }
                                        /*
                                         * 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.
                                         */
                                        dlil_send_arp_internal(ifp, ARPOP_REQUEST,
                                                (struct sockaddr_dl*)TAILQ_FIRST(&ifp->if_addrhead)->ifa_addr,
                                                (const struct sockaddr*)sender_ip, sender_hw,
                                                (const struct sockaddr*)target_ip);
                                }
                        }
                        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) {
                                error = arp_lookup_route(&sender_ip->sin_addr, 1, 0, &route);
                                if (error == 0 && route != NULL && route->rt_gateway != NULL) {
                                        created_announcement = 1;
                                }
                        }
                        if (created_announcement == 0) {
                                goto respond;
                        }
                } else {
                        goto respond;
                }
        }
        
        gateway = SDL(route->rt_gateway);
        if (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;
                        }
                        
                        /*
                         * Don't change the cloned route away from the parent's interface
                         * if the address did resolve.
                         */
                        if (gateway->sdl_alen != 0 && route->rt_parent &&
                                route->rt_parent->rt_ifp == route->rt_ifp) {
                                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;
                }
        }
        
        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 = (struct llinfo_arp*)route->rt_llinfo;
        llinfo->la_asked = 0;
        if (llinfo->la_hold) {
                struct mbuf *m0;
                m0 = llinfo->la_hold;
                llinfo->la_hold = 0;
                
                /* Should we a reference on the route first? */
                lck_mtx_unlock(rt_mtx);
                dlil_output(ifp, PF_INET, m0, (caddr_t)route, rt_key(route), 0);
                lck_mtx_lock(rt_mtx);
        }
        
respond:
        if (arpop != ARPOP_REQUEST) {
                lck_mtx_unlock(rt_mtx);
                return 0;
        }
        
        /* 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 */
                error = arp_lookup_route(&target_ip->sin_addr, 0, SIN_PROXY, &route);
                if (error || route == NULL) {
                        
                        /* 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) {
                                lck_mtx_unlock(rt_mtx);
                                return 0;
                        }
                        
                        /* See if we have a route to the target ip before we proxy it */
                        route = rtalloc1_locked((const struct sockaddr*)target_ip, 0, 0);
                        if (!route) {
                                lck_mtx_unlock(rt_mtx);
                                return 0;
                        }
                        
                        /*
                         * Don't proxy for hosts already on the same interface.
                         */
                        if (route->rt_ifp == ifp) {
                                rtfree_locked(route);
                                lck_mtx_unlock(rt_mtx);
                                return 0;
                        }
                }
        }
        lck_mtx_unlock(rt_mtx);
        
        dlil_send_arp(ifp, ARPOP_REPLY, NULL, (const struct sockaddr*)target_ip,
                sender_hw, (const struct sockaddr*)sender_ip);
        
        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);
}