/*
 * Copyright (c) 1984, 1993
 *      The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Sun Microsystems, Inc.
 *
 * 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. 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.
 *
 * @(#)from: arp.c      8.2 (Berkeley) 1/2/94
 * $FreeBSD: src/usr.sbin/arp/arp.c,v 1.22.2.12 2003/04/16 10:02:37 ru Exp $
 */

/*
 * arp - display, set, and delete arp table entries
 */


#include <sys/param.h>
#include <sys/file.h>
#include <sys/socket.h>
#include <sys/sockio.h>
#include <sys/sysctl.h>
#include <sys/ioctl.h>
#include <sys/time.h>

#include <net/if.h>
#include <net/if_dl.h>
#include <net/if_types.h>
#include <net/route.h>

#include <netinet/in.h>
#include <netinet/if_ether.h>

#include <arpa/inet.h>

#include <ctype.h>
#include <err.h>
#include <errno.h>
#include <netdb.h>
#include <nlist.h>
#include <paths.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static void search(u_long addr, void (*action)(struct sockaddr_dl *sdl,
        struct sockaddr_inarp *sin, struct rt_msghdr *rtm));
static void print_entry(struct sockaddr_dl *sdl,
        struct sockaddr_inarp *addr, struct rt_msghdr *rtm);
static void nuke_entry(struct sockaddr_dl *sdl,
        struct sockaddr_inarp *addr, struct rt_msghdr *rtm);
static int delete(char *host, char *info);
static void usage(void) __dead2;
static int set(int argc, char **argv);
static int get(char *host);
static int file(char *name);
static void getsocket(void);
static int my_ether_aton(char *a, struct ether_addr *n);
static int rtmsg(int cmd);
static int get_ether_addr(u_int32_t ipaddr, struct ether_addr *hwaddr);

static int pid;
static int nflag;       /* no reverse dns lookups */
static int aflag;       /* do it for all entries */
static int cpuflag = -1;
static int s = -1;
static int rifindex = 0;
static const char *rifname = NULL;

static struct   sockaddr_in so_mask;
static struct   sockaddr_inarp blank_sin, sin_m;
static struct   sockaddr_dl blank_sdl, sdl_m;
static int      flags, doing_proxy, proxy_only, found_entry;
static time_t   expire_time;
static struct   {
        struct  rt_msghdr m_rtm;
        char    m_space[512];
}       m_rtmsg;

/* which function we're supposed to do */
#define F_GET           1
#define F_SET           2
#define F_FILESET       3
#define F_REPLACE       4
#define F_DELETE        5

#define SETFUNC(f)      { if (func) usage(); func = (f); }

int
main(int argc, char **argv)
{
        int ch, func = 0;
        int rtn = 0;

        pid = getpid();
        while ((ch = getopt(argc, argv, "ac:i:ndfsS")) != -1)
                switch((char)ch) {
                case 'a':
                        aflag = 1;
                        break;
                case 'c':
                        cpuflag = strtol(optarg, NULL, 0);
                        break;
                case 'i':
                        rifname = optarg;
                        break;
                case 'd':
                        SETFUNC(F_DELETE);
                        break;
                case 'n':
                        nflag = 1;
                        break;
                case 'S':
                        SETFUNC(F_REPLACE);
                        break;
                case 's':
                        SETFUNC(F_SET);
                        break;
                case 'f' :
                        SETFUNC(F_FILESET);
                        break;
                case '?':
                default:
                        usage();
                }
        argc -= optind;
        argv += optind;

        bzero(&so_mask, sizeof(so_mask));
        so_mask.sin_len = 8;
        so_mask.sin_addr.s_addr = 0xffffffff;
        bzero(&blank_sin, sizeof(blank_sin));
        blank_sin.sin_len = sizeof(blank_sin);
        blank_sin.sin_family = AF_INET;
        bzero(&blank_sdl, sizeof(blank_sdl));
        blank_sdl.sdl_len = sizeof(blank_sdl);
        blank_sdl.sdl_family = AF_LINK;

        if (func == 0)
                func = F_GET;
        if (rifname != NULL) {
                if (func != F_GET && !(func == F_DELETE && aflag))
                        errx(1, "-i not applicable to this operation");
                if ((rifindex = if_nametoindex(rifname)) == 0) {
                        if (errno == ENXIO)
                                errx(1, "interface %s does not exist",
                                     rifname);
                        else
                                err(1, "if_nametoindex(%s)", rifname);
                }
        }

        switch (func) {
        case F_GET:
                if (aflag) {
                        if (argc != 0)
                                usage();
                        search(0, print_entry);
                } else {
                        if (argc != 1)
                                usage();
                        get(argv[0]);
                }
                break;
        case F_SET:
        case F_REPLACE:
                if (argc < 2 || argc > 6)
                        usage();
                if (func == F_REPLACE)
                        delete(argv[0], NULL);
                rtn = set(argc, argv) ? 1 : 0;
                break;
        case F_DELETE:
                if (aflag) {
                        if (argc != 0)
                                usage();
                        search(0, nuke_entry);
                } else {
                        if (argc < 1 || argc > 2)
                                usage();
                        rtn = delete(argv[0], argv[1]);
                }
                break;
        case F_FILESET:
                if (argc != 1)
                        usage();
                rtn = file(argv[0]);
                break;
        }

        return(rtn);
}

/*
 * Process a file to set standard arp entries
 */
static int
file(char *name)
{
        FILE *fp;
        int i, retval;
        char line[100], arg[5][50], *args[5], *p;

        if ((fp = fopen(name, "r")) == NULL)
                errx(1, "cannot open %s", name);
        args[0] = &arg[0][0];
        args[1] = &arg[1][0];
        args[2] = &arg[2][0];
        args[3] = &arg[3][0];
        args[4] = &arg[4][0];
        retval = 0;
        while(fgets(line, 100, fp) != NULL) {
                if ((p = strchr(line, '#')) != NULL)
                        *p = '\0';
                for (p = line; isblank(*p); p++);
                if (*p == '\n' || *p == '\0')
                        continue;
                i = sscanf(p, "%49s %49s %49s %49s %49s", arg[0], arg[1],
                    arg[2], arg[3], arg[4]);
                if (i < 2) {
                        warnx("bad line: %s", line);
                        retval = 1;
                        continue;
                }
                if (set(i, args))
                        retval = 1;
        }
        fclose(fp);
        return(retval);
}

static void
getsocket(void)
{
        if (s < 0) {
                s = socket(PF_ROUTE, SOCK_RAW, 0);
                if (s < 0)
                        err(1, "socket");
        }
}

/*
 * Set an individual arp entry
 */
static int
set(int argc, char **argv)
{
        struct hostent *hp;
        struct sockaddr_inarp *addr = &sin_m;
        struct sockaddr_dl *sdl;
        struct rt_msghdr *rtm = &(m_rtmsg.m_rtm);
        struct ether_addr *ea;
        char *host = argv[0], *eaddr = argv[1];

        getsocket();
        argc -= 2;
        argv += 2;
        sdl_m = blank_sdl;
        sin_m = blank_sin;
        addr->sin_addr.s_addr = inet_addr(host);
        if (addr->sin_addr.s_addr == INADDR_NONE) {
                if (!(hp = gethostbyname(host))) {
                        warnx("%s: %s", host, hstrerror(h_errno));
                        return(1);
                }
                bcopy((char *)hp->h_addr, (char *)&addr->sin_addr,
                    sizeof(addr->sin_addr));
        }
        doing_proxy = flags = proxy_only = expire_time = 0;
        while (argc-- > 0) {
                if (strncmp(argv[0], "temp", 4) == 0) {
                        struct timespec sp;

                        clock_gettime(CLOCK_MONOTONIC, &sp);
                        expire_time = sp.tv_sec + 20 * 60;
                }
                else if (strncmp(argv[0], "pub", 3) == 0) {
                        flags |= RTF_ANNOUNCE;
                        doing_proxy = 1;
                        if (argc && strncmp(argv[1], "only", 3) == 0) {
                                proxy_only = 1;
                                sin_m.sin_other = SIN_PROXY;
                                argc--; argv++;
                        }
                } else if (strncmp(argv[0], "trail", 5) == 0) {
                        printf("%s: Sending trailers is no longer supported\n",
                                host);
                }
                argv++;
        }
        ea = (struct ether_addr *)LLADDR(&sdl_m);
        if (doing_proxy && !strcmp(eaddr, "auto")) {
                if (!get_ether_addr(addr->sin_addr.s_addr, ea)) {
                        printf("no interface found for %s\n",
                               inet_ntoa(addr->sin_addr));
                        return(1);
                }
                sdl_m.sdl_alen = ETHER_ADDR_LEN;
        } else {
                if (my_ether_aton(eaddr, ea) == 0)
                        sdl_m.sdl_alen = ETHER_ADDR_LEN;
        }
tryagain:
        if (rtmsg(RTM_GET) < 0) {
                warn("%s", host);
                return(1);
        }
        addr = (struct sockaddr_inarp *)(rtm + 1);
        sdl = (struct sockaddr_dl *)(RT_ROUNDUP(addr->sin_len) + (char *)addr);
        if (addr->sin_addr.s_addr == sin_m.sin_addr.s_addr) {
                if (sdl->sdl_family == AF_LINK &&
                    (rtm->rtm_flags & RTF_LLINFO) &&
                    !(rtm->rtm_flags & RTF_GATEWAY)) switch (sdl->sdl_type) {
                case IFT_ETHER: case IFT_FDDI: case IFT_ISO88023:
                case IFT_ISO88024: case IFT_ISO88025: case IFT_L2VLAN:
                case IFT_CARP:
                        goto overwrite;
                }
                if (doing_proxy == 0) {
                        printf("set: can only proxy for %s\n", host);
                        return(1);
                }
                if (sin_m.sin_other & SIN_PROXY) {
                        printf("set: proxy entry exists for non 802 device\n");
                        return(1);
                }
                sin_m.sin_other = SIN_PROXY;
                proxy_only = 1;
                goto tryagain;
        }
overwrite:
        if (sdl->sdl_family != AF_LINK) {
                printf("cannot intuit interface index and type for %s\n", host);
                return(1);
        }
        sdl_m.sdl_type = sdl->sdl_type;
        sdl_m.sdl_index = sdl->sdl_index;
        return(rtmsg(RTM_ADD));
}

/*
 * Display an individual arp entry
 */
static int
get(char *host)
{
        struct hostent *hp;
        struct sockaddr_inarp *addr = &sin_m;

        sin_m = blank_sin;
        addr->sin_addr.s_addr = inet_addr(host);
        if (addr->sin_addr.s_addr == INADDR_NONE) {
                if (!(hp = gethostbyname(host)))
                        errx(1, "%s: %s", host, hstrerror(h_errno));
                bcopy((char *)hp->h_addr, (char *)&addr->sin_addr,
                    sizeof(addr->sin_addr));
        }
        search(addr->sin_addr.s_addr, print_entry);
        if (found_entry == 0) {
                printf("%s (%s) -- no entry",
                    host, inet_ntoa(addr->sin_addr));
                if (rifname)
                        printf(" on %s", rifname);
                printf("\n");
                return(1);
        }
        return(0);
}

/*
 * Delete an arp entry
 */
static int
delete(char *host, char *info)
{
        struct hostent *hp;
        struct sockaddr_inarp *addr = &sin_m;
        struct rt_msghdr *rtm = &m_rtmsg.m_rtm;
        struct sockaddr_dl *sdl;

        getsocket();
        sin_m = blank_sin;
        if (info) {
                if (strncmp(info, "pub", 3) == 0)
                        sin_m.sin_other = SIN_PROXY;
                else
                        usage();
        }
        addr->sin_addr.s_addr = inet_addr(host);
        if (addr->sin_addr.s_addr == INADDR_NONE) {
                if (!(hp = gethostbyname(host))) {
                        warnx("%s: %s", host, hstrerror(h_errno));
                        return(1);
                }
                bcopy((char *)hp->h_addr, (char *)&addr->sin_addr,
                    sizeof(addr->sin_addr));
        }
tryagain:
        if (rtmsg(RTM_GET) < 0) {
                warn("%s", host);
                return(1);
        }
        addr = (struct sockaddr_inarp *)(rtm + 1);
        sdl = (struct sockaddr_dl *)(RT_ROUNDUP(addr->sin_len) + (char *)addr);
        if (addr->sin_addr.s_addr == sin_m.sin_addr.s_addr) {
                if (sdl->sdl_family == AF_LINK &&
                    (rtm->rtm_flags & RTF_LLINFO) &&
                    !(rtm->rtm_flags & RTF_GATEWAY)) switch (sdl->sdl_type) {
                case IFT_ETHER: case IFT_FDDI: case IFT_ISO88023:
                case IFT_ISO88024: case IFT_ISO88025: case IFT_L2VLAN:
                case IFT_CARP:
                        goto delete;
                }
        }
        if (sin_m.sin_other & SIN_PROXY) {
                fprintf(stderr, "delete: can't locate %s\n",host);
                return(1);
        } else {
                sin_m.sin_other = SIN_PROXY;
                goto tryagain;
        }
delete:
        if (sdl->sdl_family != AF_LINK) {
                printf("cannot locate %s\n", host);
                return(1);
        }
        if (aflag && (rtm->rtm_flags & RTF_STATIC)) {
                sdl->sdl_alen = 0;
                sdl->sdl_slen = 0;
                if (rtmsg(RTM_CHANGE) == 0) {
                        printf("%s (%s) cleared\n", 
                                host, inet_ntoa(addr->sin_addr));
                        return(0);
                }
        } else {
                if (rtmsg(RTM_DELETE) == 0) {
                        printf("%s (%s) deleted\n", 
                                host, inet_ntoa(addr->sin_addr));
                        return(0);
                }
        }
        return(1);
}

/*
 * Search the arp table and do some action on matching entries
 */
static void
search(u_long addr, void (*action)(struct sockaddr_dl *sdl,
        struct sockaddr_inarp *sin, struct rt_msghdr *rtm))
{
        int mib[7];
        int miblen;
        size_t needed;
        char *lim, *buf, *next;
        struct rt_msghdr *rtm;
        struct sockaddr_inarp *sin2;
        struct sockaddr_dl *sdl;

        mib[0] = CTL_NET;
        mib[1] = PF_ROUTE;
        mib[2] = 0;
        mib[3] = AF_INET;
        mib[4] = NET_RT_FLAGS;
        mib[5] = RTF_LLINFO;
        if (cpuflag >= 0) {
            mib[6] = cpuflag;
            miblen = 7;
        } else {
            miblen = 6;
        }
        if (sysctl(mib, miblen, NULL, &needed, NULL, 0) < 0)
                errx(1, "route-sysctl-estimate");
        if ((buf = malloc(needed)) == NULL)
                errx(1, "malloc");
        if (sysctl(mib, miblen, buf, &needed, NULL, 0) < 0)
                errx(1, "actual retrieval of routing table");
        lim = buf + needed;
        for (next = buf; next < lim; next += rtm->rtm_msglen) {
                rtm = (struct rt_msghdr *)next;
                sin2 = (struct sockaddr_inarp *)(rtm + 1);
                sdl = (struct sockaddr_dl *)((char *)sin2 +
                            RT_ROUNDUP(sin2->sin_len));
                if (rifindex > 0 && rifindex != sdl->sdl_index)
                        continue;
                if (addr) {
                        if (addr != sin2->sin_addr.s_addr)
                                continue;
                        found_entry = 1;
                }
                (*action)(sdl, sin2, rtm);
        }
        free(buf);
}

/*
 * Display an arp entry
 */
static void
print_entry(struct sockaddr_dl *sdl,
        struct sockaddr_inarp *addr, struct rt_msghdr *rtm)
{
        const char *host;
        struct hostent *hp;
        char ifname[IF_NAMESIZE];

        if (nflag == 0)
                hp = gethostbyaddr(&(addr->sin_addr), sizeof(addr->sin_addr),
                    AF_INET);
        else
                hp = NULL;
        if (hp)
                host = hp->h_name;
        else {
                host = "?";
                if (h_errno == TRY_AGAIN)
                        nflag = 1;
        }
        printf("%s (%s) at ", host, inet_ntoa(addr->sin_addr));
        if (sdl->sdl_alen)
                printf("%s", ether_ntoa((struct ether_addr *)LLADDR(sdl)));
        else
                printf("(incomplete)");
        if (if_indextoname(sdl->sdl_index, ifname) != NULL)
                printf(" on %s", ifname);
        if (rtm->rtm_rmx.rmx_expire == 0)
                printf(" permanent");
        if (addr->sin_other & SIN_PROXY)
                printf(" published (proxy only)");
        if (rtm->rtm_addrs & RTA_NETMASK) {
                addr = (struct sockaddr_inarp *)
                        (RT_ROUNDUP(sdl->sdl_len) + (char *)sdl);
                if (addr->sin_addr.s_addr == 0xffffffff)
                        printf(" published");
                if (addr->sin_len != 8)
                        printf("(weird)");
        }
        switch(sdl->sdl_type) {
            case IFT_ETHER:
                printf(" [ethernet]");
                break;
            case IFT_L2VLAN:
                printf(" [vlan]");
                break;
            case IFT_CARP:
                printf(" [carp]");
            default:
                break;
        }
                
        printf("\n");

}

/*
 * Nuke an arp entry
 */
static void
nuke_entry(struct sockaddr_dl *sdl __unused,
        struct sockaddr_inarp *addr, struct rt_msghdr *rtm __unused)
{
        char ip[20];

        snprintf(ip, sizeof(ip), "%s", inet_ntoa(addr->sin_addr));
        delete(ip, NULL);
}

static int
my_ether_aton(char *a, struct ether_addr *n)
{
        struct ether_addr *ea;

        if ((ea = ether_aton(a)) == NULL) {
                warnx("invalid Ethernet address '%s'", a);
                return(1);
        }
        *n = *ea;
        return(0);
}

static void
usage(void)
{
        fprintf(stderr, "%s\n%s\n%s\n%s\n%s\n%s\n%s\n",
                "usage: arp [-n] [-c cpu] [-i interface] hostname",
                "       arp [-n] [-c cpu] [-i interface] -a",
                "       arp -d hostname [pub]",
                "       arp -d [-i interface] -a",
                "       arp -s hostname ether_addr [temp] [pub [only]]",
                "       arp -S hostname ether_addr [temp] [pub [only]]",
                "       arp -f filename");
        exit(1);
}

static int
rtmsg(int cmd)
{
        static int seq;
        int rlen;
        struct rt_msghdr *rtm = &m_rtmsg.m_rtm;
        char *cp = m_rtmsg.m_space;
        int l;

        errno = 0;
        if (cmd == RTM_DELETE || cmd == RTM_CHANGE)
                goto doit;
        bzero((char *)&m_rtmsg, sizeof(m_rtmsg));
        rtm->rtm_flags = flags;
        rtm->rtm_version = RTM_VERSION;

        switch (cmd) {
        default:
                errx(1, "internal wrong cmd");
        case RTM_ADD:
                rtm->rtm_addrs |= RTA_GATEWAY;
                rtm->rtm_rmx.rmx_expire = expire_time;
                rtm->rtm_inits = RTV_EXPIRE;
                rtm->rtm_flags |= (RTF_HOST | RTF_STATIC);
                sin_m.sin_other = 0;
                if (doing_proxy) {
                        if (proxy_only)
                                sin_m.sin_other = SIN_PROXY;
                        else {
                                rtm->rtm_addrs |= RTA_NETMASK;
                                rtm->rtm_flags &= ~RTF_HOST;
                        }
                }
                /* FALLTHROUGH */
        case RTM_GET:
                rtm->rtm_addrs |= RTA_DST;
        }

#define NEXTADDR(w, s)                                  \
        if (rtm->rtm_addrs & (w)) {                     \
                bcopy((char *)&s, cp, sizeof(s));       \
                cp += RT_ROUNDUP(sizeof(s));            \
        }

        NEXTADDR(RTA_DST, sin_m);
        NEXTADDR(RTA_GATEWAY, sdl_m);
        NEXTADDR(RTA_NETMASK, so_mask);

        rtm->rtm_msglen = cp - (char *)&m_rtmsg;
doit:
        l = rtm->rtm_msglen;
        rtm->rtm_seq = ++seq;
        rtm->rtm_type = cmd;
        if ((rlen = write(s, (char *)&m_rtmsg, l)) < 0) {
                if (errno != ESRCH || (cmd != RTM_DELETE && cmd != RTM_CHANGE)) {
                        warn("writing to routing socket");
                        return(-1);
                }
        }
        do {
                l = read(s, (char *)&m_rtmsg, sizeof(m_rtmsg));
        } while (l > 0 && (rtm->rtm_seq != seq || rtm->rtm_pid != pid));
        if (l < 0)
                warn("read from routing socket");
        return(0);
}

/*
 * get_ether_addr - get the hardware address of an interface on the
 * the same subnet as ipaddr.
 */
#define MAX_IFS         32

static int
get_ether_addr(u_int32_t ipaddr, struct ether_addr *hwaddr)
{
        struct ifreq *ifr, *ifend, *ifp;
        u_int32_t ina, mask;
        struct sockaddr_dl *dla;
        struct ifreq ifreq;
        struct ifconf ifc;
        struct ifreq ifs[MAX_IFS];
        int sock;

        sock = socket(AF_INET, SOCK_DGRAM, 0);
        if (sock < 0)
                err(1, "socket");

        ifc.ifc_len = sizeof(ifs);
        ifc.ifc_req = ifs;
        if (ioctl(sock, SIOCGIFCONF, &ifc) < 0) {
                warnx("ioctl(SIOCGIFCONF)");
                close(sock);
                return(0);
        }

        /*
        * Scan through looking for an interface with an Internet
        * address on the same subnet as `ipaddr'.
        */
        ifend = (struct ifreq *) (ifc.ifc_buf + ifc.ifc_len);
        for (ifr = ifc.ifc_req; ifr < ifend; ) {
                if (ifr->ifr_addr.sa_family == AF_INET) {
                        ina = ((struct sockaddr_in *) 
                                &ifr->ifr_addr)->sin_addr.s_addr;
                        strncpy(ifreq.ifr_name, ifr->ifr_name, 
                                sizeof(ifreq.ifr_name));
                        /*
                         * Check that the interface is up,
                         * and not point-to-point or loopback.
                         */
                        if (ioctl(sock, SIOCGIFFLAGS, &ifreq) < 0)
                                continue;
                        if ((ifreq.ifr_flags &
                             (IFF_UP|IFF_BROADCAST|IFF_POINTOPOINT|
                                        IFF_LOOPBACK|IFF_NOARP))
                             != (IFF_UP|IFF_BROADCAST))
                                goto nextif;
                        /*
                         * Get its netmask and check that it's on 
                         * the right subnet.
                         */
                        if (ioctl(sock, SIOCGIFNETMASK, &ifreq) < 0)
                                continue;
                        mask = ((struct sockaddr_in *)
                                &ifreq.ifr_addr)->sin_addr.s_addr;
                        if ((ipaddr & mask) != (ina & mask))
                                goto nextif;
                        break;
                }
nextif:
                ifr = (struct ifreq *) ((char *)&ifr->ifr_addr
                    + MAX(ifr->ifr_addr.sa_len, sizeof(ifr->ifr_addr)));
        }

        if (ifr >= ifend) {
                close(sock);
                return(0);
        }

        /*
        * Now scan through again looking for a link-level address
        * for this interface.
        */
        ifp = ifr;
        for (ifr = ifc.ifc_req; ifr < ifend; ) {
                if (strcmp(ifp->ifr_name, ifr->ifr_name) == 0
                    && ifr->ifr_addr.sa_family == AF_LINK) {
                        /*
                         * Found the link-level address - copy it out
                         */
                        dla = (struct sockaddr_dl *) &ifr->ifr_addr;
                        memcpy(hwaddr,  LLADDR(dla), dla->sdl_alen);
                        close (sock);
                        printf("using interface %s for proxy with address ",
                                ifp->ifr_name);
                        printf("%s\n", ether_ntoa(hwaddr));
                        return(dla->sdl_alen);
                }
                ifr = (struct ifreq *) ((char *)&ifr->ifr_addr
                    + MAX(ifr->ifr_addr.sa_len, sizeof(ifr->ifr_addr)));
        }
        return(0);
}