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Annotation of 43BSD/sys/netinet/if_ether.c, revision 1.1

1.1     ! root        1: /*
        !             2:  * Copyright (c) 1982, 1986 Regents of the University of California.
        !             3:  * All rights reserved.  The Berkeley software License Agreement
        !             4:  * specifies the terms and conditions for redistribution.
        !             5:  *
        !             6:  *     @(#)if_ether.c  7.1.1.1 (Berkeley) 2/27/87
        !             7:  */
        !             8: 
        !             9: /*
        !            10:  * Ethernet address resolution protocol.
        !            11:  */
        !            12: 
        !            13: #include "param.h"
        !            14: #include "systm.h"
        !            15: #include "mbuf.h"
        !            16: #include "socket.h"
        !            17: #include "time.h"
        !            18: #include "kernel.h"
        !            19: #include "errno.h"
        !            20: #include "ioctl.h"
        !            21: #include "syslog.h"
        !            22: 
        !            23: #include "../net/if.h"
        !            24: #include "in.h"
        !            25: #include "in_systm.h"
        !            26: #include "ip.h"
        !            27: #include "if_ether.h"
        !            28: 
        !            29: #define        ARPTAB_BSIZ     9               /* bucket size */
        !            30: #define        ARPTAB_NB       19              /* number of buckets */
        !            31: #define        ARPTAB_SIZE     (ARPTAB_BSIZ * ARPTAB_NB)
        !            32: struct arptab arptab[ARPTAB_SIZE];
        !            33: int    arptab_size = ARPTAB_SIZE;      /* for arp command */
        !            34: 
        !            35: /*
        !            36:  * ARP trailer negotiation.  Trailer protocol is not IP specific,
        !            37:  * but ARP request/response use IP addresses.
        !            38:  */
        !            39: #define ETHERTYPE_IPTRAILERS ETHERTYPE_TRAIL
        !            40: 
        !            41: #define        ARPTAB_HASH(a) \
        !            42:        ((u_long)(a) % ARPTAB_NB)
        !            43: 
        !            44: #define        ARPTAB_LOOK(at,addr) { \
        !            45:        register n; \
        !            46:        at = &arptab[ARPTAB_HASH(addr) * ARPTAB_BSIZ]; \
        !            47:        for (n = 0 ; n < ARPTAB_BSIZ ; n++,at++) \
        !            48:                if (at->at_iaddr.s_addr == addr) \
        !            49:                        break; \
        !            50:        if (n >= ARPTAB_BSIZ) \
        !            51:                at = 0; \
        !            52: }
        !            53: 
        !            54: /* timer values */
        !            55: #define        ARPT_AGE        (60*1)  /* aging timer, 1 min. */
        !            56: #define        ARPT_KILLC      20      /* kill completed entry in 20 mins. */
        !            57: #define        ARPT_KILLI      3       /* kill incomplete entry in 3 minutes */
        !            58: 
        !            59: u_char etherbroadcastaddr[6] = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff };
        !            60: extern struct ifnet loif;
        !            61: 
        !            62: /*
        !            63:  * Timeout routine.  Age arp_tab entries once a minute.
        !            64:  */
        !            65: arptimer()
        !            66: {
        !            67:        register struct arptab *at;
        !            68:        register i;
        !            69: 
        !            70:        timeout(arptimer, (caddr_t)0, ARPT_AGE * hz);
        !            71:        at = &arptab[0];
        !            72:        for (i = 0; i < ARPTAB_SIZE; i++, at++) {
        !            73:                if (at->at_flags == 0 || (at->at_flags & ATF_PERM))
        !            74:                        continue;
        !            75:                if (++at->at_timer < ((at->at_flags&ATF_COM) ?
        !            76:                    ARPT_KILLC : ARPT_KILLI))
        !            77:                        continue;
        !            78:                /* timer has expired, clear entry */
        !            79:                arptfree(at);
        !            80:        }
        !            81: }
        !            82: 
        !            83: /*
        !            84:  * Broadcast an ARP packet, asking who has addr on interface ac.
        !            85:  */
        !            86: arpwhohas(ac, addr)
        !            87:        register struct arpcom *ac;
        !            88:        struct in_addr *addr;
        !            89: {
        !            90:        register struct mbuf *m;
        !            91:        register struct ether_header *eh;
        !            92:        register struct ether_arp *ea;
        !            93:        struct sockaddr sa;
        !            94: 
        !            95:        if ((m = m_get(M_DONTWAIT, MT_DATA)) == NULL)
        !            96:                return;
        !            97:        m->m_len = sizeof *ea;
        !            98:        m->m_off = MMAXOFF - m->m_len;
        !            99:        ea = mtod(m, struct ether_arp *);
        !           100:        eh = (struct ether_header *)sa.sa_data;
        !           101:        bzero((caddr_t)ea, sizeof (*ea));
        !           102:        bcopy((caddr_t)etherbroadcastaddr, (caddr_t)eh->ether_dhost,
        !           103:            sizeof(eh->ether_dhost));
        !           104:        eh->ether_type = ETHERTYPE_ARP;         /* if_output will swap */
        !           105:        ea->arp_hrd = htons(ARPHRD_ETHER);
        !           106:        ea->arp_pro = htons(ETHERTYPE_IP);
        !           107:        ea->arp_hln = sizeof(ea->arp_sha);      /* hardware address length */
        !           108:        ea->arp_pln = sizeof(ea->arp_spa);      /* protocol address length */
        !           109:        ea->arp_op = htons(ARPOP_REQUEST);
        !           110:        bcopy((caddr_t)ac->ac_enaddr, (caddr_t)ea->arp_sha,
        !           111:           sizeof(ea->arp_sha));
        !           112:        bcopy((caddr_t)&ac->ac_ipaddr, (caddr_t)ea->arp_spa,
        !           113:           sizeof(ea->arp_spa));
        !           114:        bcopy((caddr_t)addr, (caddr_t)ea->arp_tpa, sizeof(ea->arp_tpa));
        !           115:        sa.sa_family = AF_UNSPEC;
        !           116:        (*ac->ac_if.if_output)(&ac->ac_if, m, &sa);
        !           117: }
        !           118: 
        !           119: int    useloopback = 1;        /* use loopback interface for local traffic */
        !           120: 
        !           121: /*
        !           122:  * Resolve an IP address into an ethernet address.  If success, 
        !           123:  * desten is filled in.  If there is no entry in arptab,
        !           124:  * set one up and broadcast a request for the IP address.
        !           125:  * Hold onto this mbuf and resend it once the address
        !           126:  * is finally resolved.  A return value of 1 indicates
        !           127:  * that desten has been filled in and the packet should be sent
        !           128:  * normally; a 0 return indicates that the packet has been
        !           129:  * taken over here, either now or for later transmission.
        !           130:  *
        !           131:  * We do some (conservative) locking here at splimp, since
        !           132:  * arptab is also altered from input interrupt service (ecintr/ilintr
        !           133:  * calls arpinput when ETHERTYPE_ARP packets come in).
        !           134:  */
        !           135: arpresolve(ac, m, destip, desten, usetrailers)
        !           136:        register struct arpcom *ac;
        !           137:        struct mbuf *m;
        !           138:        register struct in_addr *destip;
        !           139:        register u_char *desten;
        !           140:        int *usetrailers;
        !           141: {
        !           142:        register struct arptab *at;
        !           143:        register struct ifnet *ifp;
        !           144:        struct sockaddr_in sin;
        !           145:        int s, lna;
        !           146: 
        !           147:        *usetrailers = 0;
        !           148:        if (in_broadcast(*destip)) {    /* broadcast address */
        !           149:                bcopy((caddr_t)etherbroadcastaddr, (caddr_t)desten,
        !           150:                    sizeof(etherbroadcastaddr));
        !           151:                return (1);
        !           152:        }
        !           153:        lna = in_lnaof(*destip);
        !           154:        ifp = &ac->ac_if;
        !           155:        /* if for us, use software loopback driver if up */
        !           156:        if (destip->s_addr == ac->ac_ipaddr.s_addr) {
        !           157:                if (useloopback) {
        !           158:                        sin.sin_family = AF_INET;
        !           159:                        sin.sin_addr = *destip;
        !           160:                        (void) looutput(&loif, m, (struct sockaddr *)&sin);
        !           161:                        /*
        !           162:                         * The packet has already been sent and freed.
        !           163:                         */
        !           164:                        return (0);
        !           165:                } else {
        !           166:                        bcopy((caddr_t)ac->ac_enaddr, (caddr_t)desten,
        !           167:                            sizeof(ac->ac_enaddr));
        !           168:                        return (1);
        !           169:                }
        !           170:        }
        !           171:        s = splimp();
        !           172:        ARPTAB_LOOK(at, destip->s_addr);
        !           173:        if (at == 0) {                  /* not found */
        !           174:                if (ifp->if_flags & IFF_NOARP) {
        !           175:                        bcopy((caddr_t)ac->ac_enaddr, (caddr_t)desten, 3);
        !           176:                        desten[3] = (lna >> 16) & 0x7f;
        !           177:                        desten[4] = (lna >> 8) & 0xff;
        !           178:                        desten[5] = lna & 0xff;
        !           179:                        splx(s);
        !           180:                        return (1);
        !           181:                } else {
        !           182:                        at = arptnew(destip);
        !           183:                        at->at_hold = m;
        !           184:                        arpwhohas(ac, destip);
        !           185:                        splx(s);
        !           186:                        return (0);
        !           187:                }
        !           188:        }
        !           189:        at->at_timer = 0;               /* restart the timer */
        !           190:        if (at->at_flags & ATF_COM) {   /* entry IS complete */
        !           191:                bcopy((caddr_t)at->at_enaddr, (caddr_t)desten,
        !           192:                    sizeof(at->at_enaddr));
        !           193:                if (at->at_flags & ATF_USETRAILERS)
        !           194:                        *usetrailers = 1;
        !           195:                splx(s);
        !           196:                return (1);
        !           197:        }
        !           198:        /*
        !           199:         * There is an arptab entry, but no ethernet address
        !           200:         * response yet.  Replace the held mbuf with this
        !           201:         * latest one.
        !           202:         */
        !           203:        if (at->at_hold)
        !           204:                m_freem(at->at_hold);
        !           205:        at->at_hold = m;
        !           206:        arpwhohas(ac, destip);          /* ask again */
        !           207:        splx(s);
        !           208:        return (0);
        !           209: }
        !           210: 
        !           211: /*
        !           212:  * Called from 10 Mb/s Ethernet interrupt handlers
        !           213:  * when ether packet type ETHERTYPE_ARP
        !           214:  * is received.  Common length and type checks are done here,
        !           215:  * then the protocol-specific routine is called.
        !           216:  */
        !           217: arpinput(ac, m)
        !           218:        struct arpcom *ac;
        !           219:        struct mbuf *m;
        !           220: {
        !           221:        register struct arphdr *ar;
        !           222: 
        !           223:        if (ac->ac_if.if_flags & IFF_NOARP)
        !           224:                goto out;
        !           225:        IF_ADJ(m);
        !           226:        if (m->m_len < sizeof(struct arphdr))
        !           227:                goto out;
        !           228:        ar = mtod(m, struct arphdr *);
        !           229:        if (ntohs(ar->ar_hrd) != ARPHRD_ETHER)
        !           230:                goto out;
        !           231:        if (m->m_len < sizeof(struct arphdr) + 2 * ar->ar_hln + 2 * ar->ar_pln)
        !           232:                goto out;
        !           233: 
        !           234:        switch (ntohs(ar->ar_pro)) {
        !           235: 
        !           236:        case ETHERTYPE_IP:
        !           237:        case ETHERTYPE_IPTRAILERS:
        !           238:                in_arpinput(ac, m);
        !           239:                return;
        !           240: 
        !           241:        default:
        !           242:                break;
        !           243:        }
        !           244: out:
        !           245:        m_freem(m);
        !           246: }
        !           247: 
        !           248: /*
        !           249:  * ARP for Internet protocols on 10 Mb/s Ethernet.
        !           250:  * Algorithm is that given in RFC 826.
        !           251:  * In addition, a sanity check is performed on the sender
        !           252:  * protocol address, to catch impersonators.
        !           253:  * We also handle negotiations for use of trailer protocol:
        !           254:  * ARP replies for protocol type ETHERTYPE_TRAIL are sent
        !           255:  * along with IP replies if we want trailers sent to us,
        !           256:  * and also send them in response to IP replies.
        !           257:  * This allows either end to announce the desire to receive
        !           258:  * trailer packets.
        !           259:  * We reply to requests for ETHERTYPE_TRAIL protocol as well,
        !           260:  * but don't normally send requests.
        !           261:  */
        !           262: in_arpinput(ac, m)
        !           263:        register struct arpcom *ac;
        !           264:        struct mbuf *m;
        !           265: {
        !           266:        register struct ether_arp *ea;
        !           267:        struct ether_header *eh;
        !           268:        register struct arptab *at;  /* same as "merge" flag */
        !           269:        struct mbuf *mcopy = 0;
        !           270:        struct sockaddr_in sin;
        !           271:        struct sockaddr sa;
        !           272:        struct in_addr isaddr, itaddr, myaddr;
        !           273:        int proto, op, s;
        !           274: 
        !           275:        myaddr = ac->ac_ipaddr;
        !           276:        ea = mtod(m, struct ether_arp *);
        !           277:        proto = ntohs(ea->arp_pro);
        !           278:        op = ntohs(ea->arp_op);
        !           279:        isaddr.s_addr = ((struct in_addr *)ea->arp_spa)->s_addr;
        !           280:        itaddr.s_addr = ((struct in_addr *)ea->arp_tpa)->s_addr;
        !           281:        if (!bcmp((caddr_t)ea->arp_sha, (caddr_t)ac->ac_enaddr,
        !           282:          sizeof (ea->arp_sha)))
        !           283:                goto out;       /* it's from me, ignore it. */
        !           284:        if (!bcmp((caddr_t)ea->arp_sha, (caddr_t)etherbroadcastaddr,
        !           285:            sizeof (ea->arp_sha))) {
        !           286:                log(LOG_ERR,
        !           287:                    "arp: ether address is broadcast for IP address %x!\n",
        !           288:                    ntohl(isaddr.s_addr));
        !           289:                goto out;
        !           290:        }
        !           291:        if (isaddr.s_addr == myaddr.s_addr) {
        !           292:                log(LOG_ERR, "%s: %s\n",
        !           293:                        "duplicate IP address!! sent from ethernet address",
        !           294:                        ether_sprintf(ea->arp_sha));
        !           295:                itaddr = myaddr;
        !           296:                if (op == ARPOP_REQUEST)
        !           297:                        goto reply;
        !           298:                goto out;
        !           299:        }
        !           300:        s = splimp();
        !           301:        ARPTAB_LOOK(at, isaddr.s_addr);
        !           302:        if (at) {
        !           303:                bcopy((caddr_t)ea->arp_sha, (caddr_t)at->at_enaddr,
        !           304:                    sizeof(ea->arp_sha));
        !           305:                at->at_flags |= ATF_COM;
        !           306:                if (at->at_hold) {
        !           307:                        sin.sin_family = AF_INET;
        !           308:                        sin.sin_addr = isaddr;
        !           309:                        (*ac->ac_if.if_output)(&ac->ac_if, 
        !           310:                            at->at_hold, (struct sockaddr *)&sin);
        !           311:                        at->at_hold = 0;
        !           312:                }
        !           313:        }
        !           314:        if (at == 0 && itaddr.s_addr == myaddr.s_addr) {
        !           315:                /* ensure we have a table entry */
        !           316:                at = arptnew(&isaddr);
        !           317:                bcopy((caddr_t)ea->arp_sha, (caddr_t)at->at_enaddr,
        !           318:                    sizeof(ea->arp_sha));
        !           319:                at->at_flags |= ATF_COM;
        !           320:        }
        !           321:        splx(s);
        !           322: reply:
        !           323:        switch (proto) {
        !           324: 
        !           325:        case ETHERTYPE_IPTRAILERS:
        !           326:                /* partner says trailers are OK */
        !           327:                if (at)
        !           328:                        at->at_flags |= ATF_USETRAILERS;
        !           329:                /*
        !           330:                 * Reply to request iff we want trailers.
        !           331:                 */
        !           332:                if (op != ARPOP_REQUEST || ac->ac_if.if_flags & IFF_NOTRAILERS)
        !           333:                        goto out;
        !           334:                break;
        !           335: 
        !           336:        case ETHERTYPE_IP:
        !           337:                /*
        !           338:                 * Reply if this is an IP request, or if we want to send
        !           339:                 * a trailer response.
        !           340:                 */
        !           341:                if (op != ARPOP_REQUEST && ac->ac_if.if_flags & IFF_NOTRAILERS)
        !           342:                        goto out;
        !           343:        }
        !           344:        if (itaddr.s_addr == myaddr.s_addr) {
        !           345:                /* I am the target */
        !           346:                bcopy((caddr_t)ea->arp_sha, (caddr_t)ea->arp_tha,
        !           347:                    sizeof(ea->arp_sha));
        !           348:                bcopy((caddr_t)ac->ac_enaddr, (caddr_t)ea->arp_sha,
        !           349:                    sizeof(ea->arp_sha));
        !           350:        } else {
        !           351:                ARPTAB_LOOK(at, itaddr.s_addr);
        !           352:                if (at == NULL || (at->at_flags & ATF_PUBL) == 0)
        !           353:                        goto out;
        !           354:                bcopy((caddr_t)ea->arp_sha, (caddr_t)ea->arp_tha,
        !           355:                    sizeof(ea->arp_sha));
        !           356:                bcopy((caddr_t)at->at_enaddr, (caddr_t)ea->arp_sha,
        !           357:                    sizeof(ea->arp_sha));
        !           358:        }
        !           359: 
        !           360:        bcopy((caddr_t)ea->arp_spa, (caddr_t)ea->arp_tpa,
        !           361:            sizeof(ea->arp_spa));
        !           362:        bcopy((caddr_t)&itaddr, (caddr_t)ea->arp_spa,
        !           363:            sizeof(ea->arp_spa));
        !           364:        ea->arp_op = htons(ARPOP_REPLY); 
        !           365:        /*
        !           366:         * If incoming packet was an IP reply,
        !           367:         * we are sending a reply for type IPTRAILERS.
        !           368:         * If we are sending a reply for type IP
        !           369:         * and we want to receive trailers,
        !           370:         * send a trailer reply as well.
        !           371:         */
        !           372:        if (op == ARPOP_REPLY)
        !           373:                ea->arp_pro = htons(ETHERTYPE_IPTRAILERS);
        !           374:        else if (proto == ETHERTYPE_IP &&
        !           375:            (ac->ac_if.if_flags & IFF_NOTRAILERS) == 0)
        !           376:                mcopy = m_copy(m, 0, (int)M_COPYALL);
        !           377:        eh = (struct ether_header *)sa.sa_data;
        !           378:        bcopy((caddr_t)ea->arp_tha, (caddr_t)eh->ether_dhost,
        !           379:            sizeof(eh->ether_dhost));
        !           380:        eh->ether_type = ETHERTYPE_ARP;
        !           381:        sa.sa_family = AF_UNSPEC;
        !           382:        (*ac->ac_if.if_output)(&ac->ac_if, m, &sa);
        !           383:        if (mcopy) {
        !           384:                ea = mtod(mcopy, struct ether_arp *);
        !           385:                ea->arp_pro = htons(ETHERTYPE_IPTRAILERS);
        !           386:                (*ac->ac_if.if_output)(&ac->ac_if, mcopy, &sa);
        !           387:        }
        !           388:        return;
        !           389: out:
        !           390:        m_freem(m);
        !           391:        return;
        !           392: }
        !           393: 
        !           394: /*
        !           395:  * Free an arptab entry.
        !           396:  */
        !           397: arptfree(at)
        !           398:        register struct arptab *at;
        !           399: {
        !           400:        int s = splimp();
        !           401: 
        !           402:        if (at->at_hold)
        !           403:                m_freem(at->at_hold);
        !           404:        at->at_hold = 0;
        !           405:        at->at_timer = at->at_flags = 0;
        !           406:        at->at_iaddr.s_addr = 0;
        !           407:        splx(s);
        !           408: }
        !           409: 
        !           410: /*
        !           411:  * Enter a new address in arptab, pushing out the oldest entry 
        !           412:  * from the bucket if there is no room.
        !           413:  * This always succeeds since no bucket can be completely filled
        !           414:  * with permanent entries (except from arpioctl when testing whether
        !           415:  * another permanent entry will fit).
        !           416:  */
        !           417: struct arptab *
        !           418: arptnew(addr)
        !           419:        struct in_addr *addr;
        !           420: {
        !           421:        register n;
        !           422:        int oldest = -1;
        !           423:        register struct arptab *at, *ato = NULL;
        !           424:        static int first = 1;
        !           425: 
        !           426:        if (first) {
        !           427:                first = 0;
        !           428:                timeout(arptimer, (caddr_t)0, hz);
        !           429:        }
        !           430:        at = &arptab[ARPTAB_HASH(addr->s_addr) * ARPTAB_BSIZ];
        !           431:        for (n = 0; n < ARPTAB_BSIZ; n++,at++) {
        !           432:                if (at->at_flags == 0)
        !           433:                        goto out;        /* found an empty entry */
        !           434:                if (at->at_flags & ATF_PERM)
        !           435:                        continue;
        !           436:                if (at->at_timer > oldest) {
        !           437:                        oldest = at->at_timer;
        !           438:                        ato = at;
        !           439:                }
        !           440:        }
        !           441:        if (ato == NULL)
        !           442:                return (NULL);
        !           443:        at = ato;
        !           444:        arptfree(at);
        !           445: out:
        !           446:        at->at_iaddr = *addr;
        !           447:        at->at_flags = ATF_INUSE;
        !           448:        return (at);
        !           449: }
        !           450: 
        !           451: arpioctl(cmd, data)
        !           452:        int cmd;
        !           453:        caddr_t data;
        !           454: {
        !           455:        register struct arpreq *ar = (struct arpreq *)data;
        !           456:        register struct arptab *at;
        !           457:        register struct sockaddr_in *sin;
        !           458:        int s;
        !           459: 
        !           460:        if (ar->arp_pa.sa_family != AF_INET ||
        !           461:            ar->arp_ha.sa_family != AF_UNSPEC)
        !           462:                return (EAFNOSUPPORT);
        !           463:        sin = (struct sockaddr_in *)&ar->arp_pa;
        !           464:        s = splimp();
        !           465:        ARPTAB_LOOK(at, sin->sin_addr.s_addr);
        !           466:        if (at == NULL) {               /* not found */
        !           467:                if (cmd != SIOCSARP) {
        !           468:                        splx(s);
        !           469:                        return (ENXIO);
        !           470:                }
        !           471:                if (ifa_ifwithnet(&ar->arp_pa) == NULL) {
        !           472:                        splx(s);
        !           473:                        return (ENETUNREACH);
        !           474:                }
        !           475:        }
        !           476:        switch (cmd) {
        !           477: 
        !           478:        case SIOCSARP:          /* set entry */
        !           479:                if (at == NULL) {
        !           480:                        at = arptnew(&sin->sin_addr);
        !           481:                        if (ar->arp_flags & ATF_PERM) {
        !           482:                        /* never make all entries in a bucket permanent */
        !           483:                                register struct arptab *tat;
        !           484:                                
        !           485:                                /* try to re-allocate */
        !           486:                                tat = arptnew(&sin->sin_addr);
        !           487:                                if (tat == NULL) {
        !           488:                                        arptfree(at);
        !           489:                                        splx(s);
        !           490:                                        return (EADDRNOTAVAIL);
        !           491:                                }
        !           492:                                arptfree(tat);
        !           493:                        }
        !           494:                }
        !           495:                bcopy((caddr_t)ar->arp_ha.sa_data, (caddr_t)at->at_enaddr,
        !           496:                    sizeof(at->at_enaddr));
        !           497:                at->at_flags = ATF_COM | ATF_INUSE |
        !           498:                        (ar->arp_flags & (ATF_PERM|ATF_PUBL));
        !           499:                at->at_timer = 0;
        !           500:                break;
        !           501: 
        !           502:        case SIOCDARP:          /* delete entry */
        !           503:                arptfree(at);
        !           504:                break;
        !           505: 
        !           506:        case SIOCGARP:          /* get entry */
        !           507:                bcopy((caddr_t)at->at_enaddr, (caddr_t)ar->arp_ha.sa_data,
        !           508:                    sizeof(at->at_enaddr));
        !           509:                ar->arp_flags = at->at_flags;
        !           510:                break;
        !           511:        }
        !           512:        splx(s);
        !           513:        return (0);
        !           514: }
        !           515: 
        !           516: /*
        !           517:  * Convert Ethernet address to printable (loggable) representation.
        !           518:  */
        !           519: char *
        !           520: ether_sprintf(ap)
        !           521:        register u_char *ap;
        !           522: {
        !           523:        register i;
        !           524:        static char etherbuf[18];
        !           525:        register char *cp = etherbuf;
        !           526:        static char digits[] = "0123456789abcdef";
        !           527: 
        !           528:        for (i = 0; i < 6; i++) {
        !           529:                *cp++ = digits[*ap >> 4];
        !           530:                *cp++ = digits[*ap++ & 0xf];
        !           531:                *cp++ = ':';
        !           532:        }
        !           533:        *--cp = 0;
        !           534:        return (etherbuf);
        !           535: }

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