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arp.c

/*
 * arp                This file contains an implementation of the command
 *              that maintains the kernel's ARP cache.  It is derived
 *              from Berkeley UNIX arp(8), but cleaner and with sup-
 *              port for devices other than Ethernet.
 *
 * NET-TOOLS    A collection of programs that form the base set of the
 *              NET-3 Networking Distribution for the LINUX operating
 *              system.
 *
 * Version:     $Id: arp.c,v 1.23 2003/02/08 19:56:25 ecki Exp $
 *
 * Maintainer:  Bernd 'eckes' Eckenfels, <net-tools@lina.inka.de>
 *
 * Author:      Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org>
 *
 * Changes:
 *              (based on work from Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org>)
 *              Alan Cox        :       modified for NET3
 *              Andrew Tridgell :       proxy arp netmasks
 *              Bernd Eckenfels :       -n option
 *              Bernd Eckenfels :       Use only /proc for display
 *       {1.60} Bernd Eckenfels :       new arpcode (-i) for 1.3.42 but works 
 *                                      with 1.2.x, too
 *       {1.61} Bernd Eckenfels :       more verbose messages
 *       {1.62} Bernd Eckenfels :       check -t for hw adresses and try to
 *                                      explain EINVAL (jeff)
 *970125 {1.63} Bernd Eckenfels :       -a print hardwarename instead of tiltle
 *970201 {1.64} Bernd Eckenfels :       net-features.h support
 *970203 {1.65} Bernd Eckenfels :       "#define" in "#if", 
 *                                      -H|-A additional to -t|-p
 *970214 {1.66} Bernd Eckenfels :       Fix optarg required for -H and -A
 *970412 {1.67} Bernd Eckenfels :       device=""; is default
 *970514 {1.68} Bernd Eckenfels :       -N and -D
 *970517 {1.69} Bernd Eckenfels :       usage() fixed
 *970622 {1.70} Bernd Eckenfels :       arp -d priv
 *970106 {1.80} Bernd Eckenfels :       new syntax without -D and with "dev <If>",
 *                                      ATF_MAGIC, ATF_DONTPUB support. 
 *                                      Typo fix (Debian Bug#5728 Giuliano Procida)
 *970803 {1.81} Bernd Eckenfels :       removed junk comment line 1
 *970925 {1.82} Bernd Eckenfels :       include fix for libc6
 *980213 (1.83) Phil Blundell:          set ATF_COM on new entries
 *980629 (1.84) Arnaldo Carvalho de Melo: gettext instead of catgets
 *990101 {1.85} Bernd Eckenfels           fixed usage and return codes
 *990105 (1.86) Phil Blundell:            don't ignore EINVAL in arp_set
 *991121 (1.87) Bernd Eckenfels:    yes --device has a mandatory arg
 *010404 (1.88) Arnaldo Carvalho de Melo: use setlocale
 *
 *              This program is free software; you can redistribute it
 *              and/or  modify it under  the terms of  the GNU General
 *              Public  License as  published  by  the  Free  Software
 *              Foundation;  either  version 2 of the License, or  (at
 *              your option) any later version.
 */
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
/* #include <linux/netdevice.h> */
/* #include <linux/if_arp.h>    */
#include <net/if_arp.h>
#include <stdlib.h>
#include <stdio.h>
#include <errno.h>
#include <ctype.h>
#include <fcntl.h>
#include <string.h>
#include <getopt.h>
#include <unistd.h>
#include "net-support.h"
#include "pathnames.h"
#include "version.h"
#include "config.h"
#include "intl.h"
#include "util.h"

#define DFLT_AF   "inet"
#define DFLT_HW   "ether"

#define FEATURE_ARP
#include "lib/net-features.h"

char *Release = RELEASE, *Version = "arp 1.88 (2001-04-04)";

int opt_n = 0;                /* do not resolve addresses     */
int opt_N = 0;                /* use symbolic names           */
int opt_v = 0;                /* debugging output flag        */
int opt_D = 0;                /* HW-address is devicename     */
int opt_e = 0;                /* 0=BSD output, 1=new linux    */
int opt_a = 0;                /* all entries, substring match */
struct aftype *ap;            /* current address family       */
struct hwtype *hw;            /* current hardware type        */
int sockfd = 0;               /* active socket descriptor     */
int hw_set = 0;               /* flag if hw-type was set (-H) */
char device[16] = "";         /* current device               */
static void usage(void);

/* Delete an entry from the ARP cache. */
static int arp_del(char **args)
{
    char host[128];
    struct arpreq req;
    struct sockaddr sa;
    int flags = 0;
    int deleted = 0;

    memset((char *) &req, 0, sizeof(req));

    /* Resolve the host name. */
    if (*args == NULL) {
      fprintf(stderr, _("arp: need host name\n"));
      return (-1);
    }
    safe_strncpy(host, *args, (sizeof host));
    if (ap->input(0, host, &sa) < 0) {
      ap->herror(host);
      return (-1);
    }
    /* If a host has more than one address, use the correct one! */
    memcpy((char *) &req.arp_pa, (char *) &sa, sizeof(struct sockaddr));

    if (hw_set)
      req.arp_ha.sa_family = hw->type;

    req.arp_flags = ATF_PERM;
    args++;
    while (*args != NULL) {
      if (opt_v)
          fprintf(stderr, "args=%s\n", *args);
      if (!strcmp(*args, "pub")) {
          flags |= 1;
          args++;
          continue;
      }
      if (!strcmp(*args, "priv")) {
          flags |= 2;
          args++;
          continue;
      }
      if (!strcmp(*args, "temp")) {
          req.arp_flags &= ~ATF_PERM;
          args++;
          continue;
      }
      if (!strcmp(*args, "trail")) {
          req.arp_flags |= ATF_USETRAILERS;
          args++;
          continue;
      }
      if (!strcmp(*args, "dontpub")) {
#ifdef HAVE_ATF_DONTPUB
          req.arp_flags |= ATF_DONTPUB;
#else
          ENOSUPP("arp", "ATF_DONTPUB");
#endif
          args++;
          continue;
      }
      if (!strcmp(*args, "auto")) {
#ifdef HAVE_ATF_MAGIC
          req.arp_flags |= ATF_MAGIC;
#else
          ENOSUPP("arp", "ATF_MAGIC");
#endif
          args++;
          continue;
      }
      if (!strcmp(*args, "dev")) {
          if (*++args == NULL)
            usage();
          safe_strncpy(device, *args, sizeof(device));
          args++;
          continue;
      }
      if (!strcmp(*args, "netmask")) {
          if (*++args == NULL)
            usage();
          if (strcmp(*args, "255.255.255.255") != 0) {
            strcpy(host, *args);
            if (ap->input(0, host, &sa) < 0) {
                ap->herror(host);
                return (-1);
            }
            memcpy((char *) &req.arp_netmask, (char *) &sa,
                   sizeof(struct sockaddr));
            req.arp_flags |= ATF_NETMASK;
          }
          args++;
          continue;
      }
      usage();
    }

    // if neighter priv nor pub is given, work on both
    if (flags == 0)
      flags = 3;

    strcpy(req.arp_dev, device);

    /* unfortuatelly the kernel interface does not allow us to
       delete private entries anlone, so we need this hack
       to avoid "not found" errors if we try both. */
    deleted = 0;

    /* Call the kernel. */
    if (flags & 2) {
      if (opt_v)
          fprintf(stderr, "arp: SIOCDARP(nopub)\n");
      if (ioctl(sockfd, SIOCDARP, &req) < 0) {
          if ((errno == ENXIO) || (errno == ENOENT)) {
            if (flags & 1)
                goto nopub;
            printf(_("No ARP entry for %s\n"), host);
            return (-1);
          }
          perror("SIOCDARP(nopub)");
          return (-1);
      } else
        deleted = 1;
    }
    if (!deleted && (flags & 1)) {
      nopub:
      req.arp_flags |= ATF_PUBL;
      if (opt_v)
          fprintf(stderr, "arp: SIOCDARP(pub)\n");
      if (ioctl(sockfd, SIOCDARP, &req) < 0) {
          if ((errno == ENXIO) || (errno == ENOENT)) {
            printf(_("No ARP entry for %s\n"), host);
            return (-1);
          }
          perror("SIOCDARP(pub)");
          return (-1);
      }
    }
    return (0);
}

/* Get the hardware address to a specified interface name */
static int arp_getdevhw(char *ifname, struct sockaddr *sa, struct hwtype *hw)
{
    struct ifreq ifr;
    struct hwtype *xhw;

    strcpy(ifr.ifr_name, ifname);
    if (ioctl(sockfd, SIOCGIFHWADDR, &ifr) < 0) {
      fprintf(stderr, _("arp: cant get HW-Address for `%s': %s.\n"), ifname, strerror(errno));
      return (-1);
    }
    if (hw && (ifr.ifr_hwaddr.sa_family != hw->type)) {
      fprintf(stderr, _("arp: protocol type mismatch.\n"));
      return (-1);
    }
    memcpy((char *) sa, (char *) &(ifr.ifr_hwaddr), sizeof(struct sockaddr));

    if (opt_v) {
      if (!(xhw = get_hwntype(ifr.ifr_hwaddr.sa_family)) || (xhw->print == 0)) {
          xhw = get_hwntype(-1);
      }
      fprintf(stderr, _("arp: device `%s' has HW address %s `%s'.\n"), ifname, xhw->name, xhw->print((char *)&ifr.ifr_hwaddr.sa_data));
    }
    return (0);
}

/* Set an entry in the ARP cache. */
static int arp_set(char **args)
{
    char host[128];
    struct arpreq req;
    struct sockaddr sa;
    int flags;

    memset((char *) &req, 0, sizeof(req));

    /* Resolve the host name. */
    if (*args == NULL) {
      fprintf(stderr, _("arp: need host name\n"));
      return (-1);
    }
    safe_strncpy(host, *args++, (sizeof host));
    if (ap->input(0, host, &sa) < 0) {
      ap->herror(host);
      return (-1);
    }
    /* If a host has more than one address, use the correct one! */
    memcpy((char *) &req.arp_pa, (char *) &sa, sizeof(struct sockaddr));

    /* Fetch the hardware address. */
    if (*args == NULL) {
      fprintf(stderr, _("arp: need hardware address\n"));
      return (-1);
    }
    if (opt_D) {
      if (arp_getdevhw(*args++, &req.arp_ha, hw_set ? hw : NULL) < 0)
          return (-1);
    } else {
      if (hw->input(*args++, &req.arp_ha) < 0) {
          fprintf(stderr, _("arp: invalid hardware address\n"));
          return (-1);
      }
    }

    /* Check out any modifiers. */
    flags = ATF_PERM | ATF_COM;
    while (*args != NULL) {
      if (!strcmp(*args, "temp")) {
          flags &= ~ATF_PERM;
          args++;
          continue;
      }
      if (!strcmp(*args, "pub")) {
          flags |= ATF_PUBL;
          args++;
          continue;
      }
      if (!strcmp(*args, "priv")) {
          flags &= ~ATF_PUBL;
          args++;
          continue;
      }
      if (!strcmp(*args, "trail")) {
          flags |= ATF_USETRAILERS;
          args++;
          continue;
      }
      if (!strcmp(*args, "dontpub")) {
#ifdef HAVE_ATF_DONTPUB
          flags |= ATF_DONTPUB;
#else
          ENOSUPP("arp", "ATF_DONTPUB");
#endif
          args++;
          continue;
      }
      if (!strcmp(*args, "auto")) {
#ifdef HAVE_ATF_MAGIC
          flags |= ATF_MAGIC;
#else
          ENOSUPP("arp", "ATF_MAGIC");
#endif
          args++;
          continue;
      }
      if (!strcmp(*args, "dev")) {
          if (*++args == NULL)
            usage();
          safe_strncpy(device, *args, sizeof(device));
          args++;
          continue;
      }
      if (!strcmp(*args, "netmask")) {
          if (*++args == NULL)
            usage();
          if (strcmp(*args, "255.255.255.255") != 0) {
            strcpy(host, *args);
            if (ap->input(0, host, &sa) < 0) {
                ap->herror(host);
                return (-1);
            }
            memcpy((char *) &req.arp_netmask, (char *) &sa,
                   sizeof(struct sockaddr));
            flags |= ATF_NETMASK;
          }
          args++;
          continue;
      }
      usage();
    }

    /* Fill in the remainder of the request. */
    req.arp_flags = flags;

    strcpy(req.arp_dev, device);

    /* Call the kernel. */
    if (opt_v)
      fprintf(stderr, "arp: SIOCSARP()\n");
    if (ioctl(sockfd, SIOCSARP, &req) < 0) {
        perror("SIOCSARP");
      return (-1);
    }
    return (0);
}


/* Process an EtherFile */
static int arp_file(char *name)
{
    char buff[1024];
    char *sp, *args[32];
    int linenr, argc;
    FILE *fp;

    if ((fp = fopen(name, "r")) == NULL) {
      fprintf(stderr, _("arp: cannot open etherfile %s !\n"), name);
      return (-1);
    }
    /* Read the lines in the file. */
    linenr = 0;
    while (fgets(buff, sizeof(buff), fp) != (char *) NULL) {
      linenr++;
      if (opt_v == 1)
          fprintf(stderr, ">> %s", buff);
      if ((sp = strchr(buff, '\n')) != (char *) NULL)
          *sp = '\0';
      if (buff[0] == '#' || buff[0] == '\0')
          continue;

      argc = getargs(buff, args);
      if (argc < 2) {
          fprintf(stderr, _("arp: format error on line %u of etherfile %s !\n"),
                linenr, name);
          continue;
      }
      if (strchr (args[0], ':') != NULL) {
          /* We have a correct ethers file, switch hw adress and hostname
             for arp */
          char *cp;
          cp = args[1];
          args[1] = args[0];
          args[0] = cp;
      }
      if (arp_set(args) != 0)
          fprintf(stderr, _("arp: cannot set entry on line %u of etherfile %s !\n"),
                linenr, name);
    }

    (void) fclose(fp);
    return (0);
}


/* Print the contents of an ARP request block. */
static void arp_disp_2(char *name, int type, int arp_flags, char *hwa, char *mask, char *dev)
{
    static int title = 0;
    struct hwtype *xhw;
    char flags[10];

    xhw = get_hwntype(type);
    if (xhw == NULL)
      xhw = get_hwtype(DFLT_HW);

    if (title++ == 0) {
      printf(_("Address                  HWtype  HWaddress           Flags Mask            Iface\n"));
    }
    /* Setup the flags. */
    flags[0] = '\0';
    if (arp_flags & ATF_COM)
      strcat(flags, "C");
    if (arp_flags & ATF_PERM)
      strcat(flags, "M");
    if (arp_flags & ATF_PUBL)
      strcat(flags, "P");
#ifdef HAVE_ATF_MAGIC
    if (arp_flags & ATF_MAGIC)
      strcat(flags, "A");
#endif
#ifdef HAVE_ATF_DONTPUB
    if (arp_flags & ATF_DONTPUB)
      strcat(flags, "!");
#endif
    if (arp_flags & ATF_USETRAILERS)
      strcat(flags, "T");

    if (!(arp_flags & ATF_NETMASK))
      mask = "";

    printf("%-23.23s  ", name);

    if (!(arp_flags & ATF_COM)) {
      if (arp_flags & ATF_PUBL)
          printf("%-8.8s%-20.20s", "*", _("<from_interface>"));
      else
          printf("%-8.8s%-20.20s", "", _("(incomplete)"));
    } else {
      printf("%-8.8s%-20.20s", xhw->name, hwa);
    }

    printf("%-6.6s%-15.15s %s\n", flags, mask, dev);
}

/* Print the contents of an ARP request block. */
static void arp_disp(char *name, char *ip, int type, int arp_flags, char *hwa, char *mask, char *dev)
{
    struct hwtype *xhw;

    xhw = get_hwntype(type);
    if (xhw == NULL)
      xhw = get_hwtype(DFLT_HW);

    printf(_("%s (%s) at "), name, ip);

    if (!(arp_flags & ATF_COM)) {
      if (arp_flags & ATF_PUBL)
          printf("<from_interface> ");
      else
          printf(_("<incomplete> "));
    } else {
      printf("%s [%s] ", hwa, xhw->name);
    }

    if (arp_flags & ATF_NETMASK)
      printf(_("netmask %s "), mask);

    if (arp_flags & ATF_PERM)
      printf("PERM ");
    if (arp_flags & ATF_PUBL)
      printf("PUB ");
#ifdef HAVE_ATF_MAGIC
    if (arp_flags & ATF_MAGIC)
      printf("AUTO ");
#endif
#ifdef HAVE_ATF_DONTPUB
    if (arp_flags & ATF_DONTPUB)
      printf("DONTPUB ");
#endif
    if (arp_flags & ATF_USETRAILERS)
      printf("TRAIL ");

    printf(_("on %s\n"), dev);
}


/* Display the contents of the ARP cache in the kernel. */
static int arp_show(char *name)
{
    char host[100];
    struct sockaddr sa;
    char ip[100];
    char hwa[100];
    char mask[100];
    char line[200];
    char dev[100];
    int type, flags;
    FILE *fp;
    char *hostname;
    int num, entries = 0, showed = 0;

    host[0] = '\0';

    if (name != NULL) {
      /* Resolve the host name. */
      safe_strncpy(host, name, (sizeof host));
      if (ap->input(0, host, &sa) < 0) {
          ap->herror(host);
          return (-1);
      }
      safe_strncpy(host, ap->sprint(&sa, 1), sizeof(host));
    }
    /* Open the PROCps kernel table. */
    if ((fp = fopen(_PATH_PROCNET_ARP, "r")) == NULL) {
      perror(_PATH_PROCNET_ARP);
      return (-1);
    }
    /* Bypass header -- read until newline */
    if (fgets(line, sizeof(line), fp) != (char *) NULL) {
      strcpy(mask, "-");
      strcpy(dev, "-");
      /* Read the ARP cache entries. */
      for (; fgets(line, sizeof(line), fp);) {
          num = sscanf(line, "%s 0x%x 0x%x %100s %100s %100s\n",
                   ip, &type, &flags, hwa, mask, dev);
          if (num < 4)
            break;

          entries++;
          /* if the user specified hw-type differs, skip it */
          if (hw_set && (type != hw->type))
            continue;

          /* if the user specified address differs, skip it */
          if (host[0] && strcmp(ip, host))
            continue;

          /* if the user specified device differs, skip it */
          if (device[0] && strcmp(dev, device))
            continue;

          showed++;
          /* This IS ugly but it works -be */
          if (opt_n)
            hostname = "?";
          else {
            if (ap->input(0, ip, &sa) < 0)
                hostname = ip;
            else
                hostname = ap->sprint(&sa, opt_n | 0x8000);
            if (strcmp(hostname, ip) == 0)
                hostname = "?";
          }

          if (opt_e)
            arp_disp_2(hostname[0] == '?' ? ip : hostname, type, flags, hwa, mask, dev);
          else
            arp_disp(hostname, ip, type, flags, hwa, mask, dev);
      }
    }
    if (opt_v)
      printf(_("Entries: %d\tSkipped: %d\tFound: %d\n"), entries, entries - showed, showed);

    if (!showed) {
      if (host[0] && !opt_a)
          printf(_("%s (%s) -- no entry\n"), name, host);
      else if (hw_set || host[0] || device[0]) {
          printf(_("arp: in %d entries no match found.\n"), entries);
      }
    }
    (void) fclose(fp);
    return (0);
}

static void version(void)
{
    fprintf(stderr, "%s\n%s\n%s\n", Release, Version, Features);
    exit(E_VERSION);
}

static void usage(void)
{
    fprintf(stderr, _("Usage:\n  arp [-vn]  [<HW>] [-i <if>] [-a] [<hostname>]             <-Display ARP cache\n"));
    fprintf(stderr, _("  arp [-v]          [-i <if>] -d  <hostname> [pub][nopub]    <-Delete ARP entry\n"));
    fprintf(stderr, _("  arp [-vnD] [<HW>] [-i <if>] -f  [<filename>]            <-Add entry from file\n"));
    fprintf(stderr, _("  arp [-v]   [<HW>] [-i <if>] -s  <hostname> <hwaddr> [temp][nopub] <-Add entry\n"));
    fprintf(stderr, _("  arp [-v]   [<HW>] [-i <if>] -Ds <hostname> <if> [netmask <nm>] pub      <-''-\n\n"));
    
    fprintf(stderr, _("        -a                       display (all) hosts in alternative (BSD) style\n"));
    fprintf(stderr, _("        -s, --set                set a new ARP entry\n"));
    fprintf(stderr, _("        -d, --delete             delete a specified entry\n"));
    fprintf(stderr, _("        -v, --verbose            be verbose\n"));
    fprintf(stderr, _("        -n, --numeric            don't resolve names\n"));
    fprintf(stderr, _("        -i, --device             specify network interface (e.g. eth0)\n"));
    fprintf(stderr, _("        -D, --use-device         read <hwaddr> from given device\n"));
    fprintf(stderr, _("        -A, -p, --protocol       specify protocol family\n"));
    fprintf(stderr, _("        -f, --file               read new entries from file or from /etc/ethers\n\n"));

    fprintf(stderr, _("  <HW>=Use '-H <hw>' to specify hardware address type. Default: %s\n"), DFLT_HW);
    fprintf(stderr, _("  List of possible hardware types (which support ARP):\n"));
    print_hwlist(1); /* 1 = ARPable */
    exit(E_USAGE);
}

int main(int argc, char **argv)
{
    int i, lop, what;
    struct option longopts[] =
    {
      {"verbose", 0, 0, 'v'},
      {"version", 0, 0, 'V'},
      {"all", 0, 0, 'a'},
      {"delete", 0, 0, 'd'},
      {"file", 0, 0, 'f'},
      {"numeric", 0, 0, 'n'},
      {"set", 0, 0, 's'},
      {"protocol", 1, 0, 'A'},
      {"hw-type", 1, 0, 'H'},
      {"device", 1, 0, 'i'},
      {"help", 0, 0, 'h'},
      {"use-device", 0, 0, 'D'},
      {"symbolic", 0, 0, 'N'},
      {NULL, 0, 0, 0}
    };

#if I18N
    setlocale (LC_ALL, "");
    bindtextdomain("net-tools", "/usr/share/locale");
    textdomain("net-tools");
#endif

    /* Initialize variables... */
    if ((hw = get_hwtype(DFLT_HW)) == NULL) {
      fprintf(stderr, _("%s: hardware type not supported!\n"), DFLT_HW);
      return (-1);
    }
    if ((ap = get_aftype(DFLT_AF)) == NULL) {
      fprintf(stderr, _("%s: address family not supported!\n"), DFLT_AF);
      return (-1);
    }
    what = 0;

    /* Fetch the command-line arguments. */
    /* opterr = 0; */
    while ((i = getopt_long(argc, argv, "A:H:adfp:nsei:t:vh?DNV", longopts, &lop)) != EOF)
      switch (i) {
      case 'a':
          what = 1;
          opt_a = 1;
          break;
      case 'f':
          what = 2;
          break;
      case 'd':
          what = 3;
          break;
      case 's':
          what = 4;
          break;


      case 'e':
          opt_e = 1;
          break;
      case 'n':
          opt_n = FLAG_NUM;
          break;
      case 'D':
          opt_D = 1;
          break;
      case 'N':
          opt_N = FLAG_SYM;
          fprintf(stderr, _("arp: -N not yet supported.\n"));
          break;
      case 'v':
          opt_v = 1;
          break;

      case 'A':
      case 'p':
          ap = get_aftype(optarg);
          if (ap == NULL) {
            fprintf(stderr, _("arp: %s: unknown address family.\n"),
                  optarg);
            exit(-1);
          }
          break;
      case 'H':
      case 't':
          hw = get_hwtype(optarg);
          if (hw == NULL) {
            fprintf(stderr, _("arp: %s: unknown hardware type.\n"),
                  optarg);
            exit(-1);
          }
          hw_set = 1;
          break;
      case 'i':
          safe_strncpy(device, optarg, sizeof(device));
          break;

      case 'V':
          version();
      case '?':
      case 'h':
      default:
          usage();
      }

    if (ap->af != AF_INET) {
      fprintf(stderr, _("arp: %s: kernel only supports 'inet'.\n"),
            ap->name);
      exit(-1);
    }

    /* If not hw type specified get default */
    if(hw_set==0)
      if ((hw = get_hwtype(DFLT_HW)) == NULL) {
        fprintf(stderr, _("%s: hardware type not supported!\n"), DFLT_HW);
        return (-1);
      }

    if (hw->alen <= 0) {
      fprintf(stderr, _("arp: %s: hardware type without ARP support.\n"),
            hw->name);
      exit(-1);
    }
    if ((sockfd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
      perror("socket");
      exit(-1);
    }
    /* Now see what we have to do here... */
    switch (what) {
    case 0:
      opt_e = 1;
      what = arp_show(argv[optind]);
      break;

    case 1:             /* show an ARP entry in the cache */
      what = arp_show(argv[optind]);
      break;

    case 2:             /* process an EtherFile */
      what = arp_file(argv[optind] ? argv[optind] : "/etc/ethers");
      break;

    case 3:             /* delete an ARP entry from the cache */
      what = arp_del(&argv[optind]);
      break;

    case 4:             /* set an ARP entry in the cache */
      what = arp_set(&argv[optind]);
      break;

    default:
      usage();
    }

    exit(what);
}

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