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/*
 * 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 1.1 2002-03-17 19:58:52 simons 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
 *
 *              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 1.85 (1999-01-05)";
 
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 err;
 
    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 (flags == 0)
	flags = 3;
 
    strcpy(req.arp_dev, device);
 
    err = -1;
 
    /* Call the kernel. */
    if (flags & 2) {
	if (opt_v)
	    fprintf(stderr, "arp: SIOCDARP(nopub)\n");
	if ((err = ioctl(sockfd, SIOCDARP, &req) < 0)) {
	    if (errno == ENXIO) {
		if (flags & 1)
		    goto nopub;
		printf(_("No ARP entry for %s\n"), host);
		return (-1);
	    }
	    perror("SIOCDARP(priv)");
	    return (-1);
	}
    }
    if ((flags & 1) && (err)) {
      nopub:
	req.arp_flags |= ATF_PUBL;
	if (opt_v)
	    fprintf(stderr, "arp: SIOCDARP(pub)\n");
	if (ioctl(sockfd, SIOCDARP, &req) < 0) {
	    if (errno == ENXIO) {
		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->sprint == 0)) {
	    xhw = get_hwntype(-1);
	}
	fprintf(stderr, _("arp: device `%s' has HW address %s `%s'.\n"), ifname, xhw->name, xhw->sprint(&ifr.ifr_hwaddr));
    }
    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 (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\t\t\tHWtype\tHWaddress\t    Flags Mask\t\t  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\t", name);
 
    if (!(arp_flags & ATF_COM)) {
	if (arp_flags & ATF_PUBL)
	    printf("%-8.8s%-20.20s", "*", "*");
	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("* ");
	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("PUP ");
#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);
	}
	strcpy(host, ap->sprint(&sa, 1));
    }
    /* 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>] -s  <hostname> <hwaddr> [netmask <nm>] pub  <-''-\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            dont 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, _("        -f, --file               read new entries from file\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;
#ifdef EMBED
#define	getopt_long(a,b,c,d,e)	getopt(a,b,c)
#else
    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", 0, 0, 'i'},
	{"help", 0, 0, 'h'},
	{"use-device", 0, 0, 'D'},
	{"symbolic", 0, 0, 'N'},
	{NULL, 0, 0, 0}
    };
#endif
 
#if I18N
    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 (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]);
	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);
}