/*-
 * SPDX-License-Identifier: BSD-3-Clause
 *
 * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the project 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 PROJECT 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 PROJECT 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.
 *
 *      $KAME: nd6_nbr.c,v 1.86 2002/01/21 02:33:04 jinmei Exp $
 */

#include "opt_inet.h"
#include "opt_inet6.h"
#include "opt_ipsec.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/counter.h>
#include <sys/eventhandler.h>
#include <sys/malloc.h>
#include <sys/libkern.h>
#include <sys/lock.h>
#include <sys/rwlock.h>
#include <sys/mbuf.h>
#include <sys/socket.h>
#include <sys/sockio.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <sys/errno.h>
#include <sys/sysctl.h>
#include <sys/syslog.h>
#include <sys/queue.h>
#include <sys/callout.h>
#include <sys/refcount.h>

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

#include <netinet/in.h>
#include <netinet/in_var.h>
#include <net/if_llatbl.h>
#include <netinet6/in6_var.h>
#include <netinet6/in6_ifattach.h>
#include <netinet/ip6.h>
#include <netinet6/ip6_var.h>
#include <netinet6/scope6_var.h>
#include <netinet6/nd6.h>
#include <netinet/icmp6.h>
#include <netinet/ip_carp.h>
#include <netinet6/send.h>

#include <machine/atomic.h>

#define SDL(s) ((struct sockaddr_dl *)s)

MALLOC_DECLARE(M_IP6NDP);

struct dadq;
static struct dadq *nd6_dad_find(struct ifaddr *, struct nd_opt_nonce *);
static void nd6_dad_add(struct dadq *dp);
static void nd6_dad_del(struct dadq *dp);
static void nd6_dad_rele(struct dadq *);
static void nd6_dad_starttimer(struct dadq *, int);
static void nd6_dad_stoptimer(struct dadq *);
static void nd6_dad_timer(void *);
static void nd6_dad_duplicated(struct ifaddr *, struct dadq *);
static void nd6_dad_ns_output(struct dadq *);
static void nd6_dad_ns_input(struct ifaddr *, struct nd_opt_nonce *);
static void nd6_dad_na_input(struct ifaddr *);
static void nd6_na_output_fib(struct ifnet *, const struct in6_addr *,
    const struct in6_addr *, u_long, int, struct sockaddr *, u_int);
static void nd6_ns_output_fib(struct ifnet *, const struct in6_addr *,
    const struct in6_addr *, const struct in6_addr *, uint8_t *, u_int);
static void nd6_queue_add(struct ifaddr *, struct in6_addr *,
    struct in6_addr *, struct sockaddr_dl *, int, uint32_t);

static struct ifaddr *nd6_proxy_fill_sdl(struct ifnet *,
    const struct in6_addr *, struct sockaddr_dl *);

VNET_DEFINE_STATIC(int, dad_enhanced) = 1;
#define V_dad_enhanced                  VNET(dad_enhanced)

SYSCTL_DECL(_net_inet6_ip6);
SYSCTL_INT(_net_inet6_ip6, OID_AUTO, dad_enhanced, CTLFLAG_VNET | CTLFLAG_RW,
    &VNET_NAME(dad_enhanced), 0,
    "Enable Enhanced DAD, which adds a random nonce to NS messages for DAD.");

VNET_DEFINE_STATIC(int, dad_maxtry) = 15;       /* max # of *tries* to
                                                   transmit DAD packet */
#define V_dad_maxtry                    VNET(dad_maxtry)

VNET_DEFINE_STATIC(int, nd6_onlink_ns_rfc4861) = 0;
#define V_nd6_onlink_ns_rfc4861         VNET(nd6_onlink_ns_rfc4861)
SYSCTL_INT(_net_inet6_icmp6, ICMPV6CTL_ND6_ONLINKNSRFC4861,
    nd6_onlink_ns_rfc4861, CTLFLAG_VNET | CTLFLAG_RW,
    &VNET_NAME(nd6_onlink_ns_rfc4861), 0,
    "Accept 'on-link' ICMPv6 NS messages in compliance with RFC 4861");

struct nd_queue {
        TAILQ_ENTRY(nd_queue) ndq_list;
        struct ifaddr           *ndq_ifa;
        struct in6_addr         ndq_daddr;
        struct in6_addr         ndq_taddr;
        struct sockaddr_dl      ndq_sdl;
        uint32_t                ndq_flags;
        struct callout          ndq_callout;
};

/*
 * Input a Neighbor Solicitation Message.
 *
 * Based on RFC 2461
 * Based on RFC 2462 (duplicate address detection)
 */
void
nd6_ns_input(struct mbuf *m, int off, int icmp6len)
{
        struct ifnet *ifp;
        struct ip6_hdr *ip6;
        struct nd_neighbor_solicit *nd_ns;
        struct in6_addr daddr6, myaddr6, saddr6, taddr6;
        struct ifaddr *ifa;
        struct sockaddr_dl proxydl;
        union nd_opts ndopts;
        char ip6bufs[INET6_ADDRSTRLEN], ip6bufd[INET6_ADDRSTRLEN];
        char *lladdr;
        int lladdrlen, rflag, tentative, tlladdr;
        uint32_t dflags;

        ifa = NULL;

        /* RFC 6980: Nodes MUST silently ignore fragments */
        if(m->m_flags & M_FRAGMENTED)
                goto freeit;

        ifp = m->m_pkthdr.rcvif;
        ip6 = mtod(m, struct ip6_hdr *);
        if (__predict_false(ip6->ip6_hlim != 255)) {
                ICMP6STAT_INC(icp6s_invlhlim);
                nd6log((LOG_ERR,
                    "nd6_ns_input: invalid hlim (%d) from %s to %s on %s\n",
                    ip6->ip6_hlim, ip6_sprintf(ip6bufs, &ip6->ip6_src),
                    ip6_sprintf(ip6bufd, &ip6->ip6_dst), if_name(ifp)));
                goto bads;
        }

        if (m->m_len < off + icmp6len) {
                m = m_pullup(m, off + icmp6len);
                if (m == NULL) {
                        IP6STAT_INC(ip6s_exthdrtoolong);
                        return;
                }
        }
        ip6 = mtod(m, struct ip6_hdr *);
        nd_ns = (struct nd_neighbor_solicit *)((caddr_t)ip6 + off);

        saddr6 = ip6->ip6_src;
        daddr6 = ip6->ip6_dst;
        taddr6 = nd_ns->nd_ns_target;
        if (in6_setscope(&taddr6, ifp, NULL) != 0)
                goto bad;

        rflag = (V_ip6_forwarding) ? ND_NA_FLAG_ROUTER : 0;
        if (ifp->if_inet6->nd_flags & ND6_IFF_ACCEPT_RTADV && V_ip6_norbit_raif)
                rflag = 0;

        if (IN6_IS_ADDR_UNSPECIFIED(&saddr6)) {
                /* dst has to be a solicited node multicast address. */
                if (daddr6.s6_addr16[0] == IPV6_ADDR_INT16_MLL &&
                    /* don't check ifindex portion */
                    daddr6.s6_addr32[1] == 0 &&
                    daddr6.s6_addr32[2] == IPV6_ADDR_INT32_ONE &&
                    daddr6.s6_addr8[12] == 0xff) {
                        ; /* good */
                } else {
                        nd6log((LOG_INFO, "nd6_ns_input: bad DAD packet "
                            "(wrong ip6 dst)\n"));
                        goto bad;
                }
        } else if (!V_nd6_onlink_ns_rfc4861) {
                struct sockaddr_in6 src_sa6;

                /*
                 * According to recent IETF discussions, it is not a good idea
                 * to accept a NS from an address which would not be deemed
                 * to be a neighbor otherwise.  This point is expected to be
                 * clarified in future revisions of the specification.
                 */
                bzero(&src_sa6, sizeof(src_sa6));
                src_sa6.sin6_family = AF_INET6;
                src_sa6.sin6_len = sizeof(src_sa6);
                src_sa6.sin6_addr = saddr6;
                if (nd6_is_addr_neighbor(&src_sa6, ifp) == 0) {
                        nd6log((LOG_INFO, "nd6_ns_input: "
                                "NS packet from non-neighbor\n"));
                        goto bad;
                }
        }

        if (IN6_IS_ADDR_MULTICAST(&taddr6)) {
                nd6log((LOG_INFO, "nd6_ns_input: bad NS target (multicast)\n"));
                goto bad;
        }

        icmp6len -= sizeof(*nd_ns);
        nd6_option_init(nd_ns + 1, icmp6len, &ndopts);
        if (nd6_options(&ndopts) < 0) {
                nd6log((LOG_INFO,
                    "nd6_ns_input: invalid ND option, ignored\n"));
                /* nd6_options have incremented stats */
                goto freeit;
        }

        lladdr = NULL;
        lladdrlen = 0;
        if (ndopts.nd_opts_src_lladdr) {
                lladdr = (char *)(ndopts.nd_opts_src_lladdr + 1);
                lladdrlen = ndopts.nd_opts_src_lladdr->nd_opt_len << 3;
        }

        if (IN6_IS_ADDR_UNSPECIFIED(&ip6->ip6_src) && lladdr) {
                nd6log((LOG_INFO, "nd6_ns_input: bad DAD packet "
                    "(link-layer address option)\n"));
                goto bad;
        }

        /*
         * Attaching target link-layer address to the NA?
         * (RFC 2461 7.2.4)
         *
         * NS IP dst is unicast/anycast                 MUST NOT add
         * NS IP dst is solicited-node multicast        MUST add
         *
         * In implementation, we add target link-layer address by default.
         * We do not add one in MUST NOT cases.
         */
        tlladdr = 0;
        if (IN6_IS_ADDR_MULTICAST(&daddr6))
                tlladdr |= ND6_NA_OPT_LLA;

        /*
         * Target address (taddr6) must be either:
         * (1) Valid unicast/anycast address for my receiving interface,
         * (2) Unicast address for which I'm offering proxy service, or
         * (3) "tentative" address on which DAD is being performed.
         */
        /* (1) and (3) check. */
        if (ifp->if_carp) {
                ifa = (*carp_iamatch6_p)(ifp, &taddr6);
                if (ifa != NULL)
                        tlladdr |= ND6_NA_CARP_MASTER;
        } else
                ifa = (struct ifaddr *)in6ifa_ifpwithaddr(ifp, &taddr6);

        /* (2) check. */
        dflags = 0;
        if (ifa == NULL) {
                if ((ifa = nd6_proxy_fill_sdl(ifp, &taddr6, &proxydl)) != NULL)
                        dflags |= ND6_QUEUE_FLAG_PROXY;
        }
        if (ifa == NULL) {
                /*
                 * We've got an NS packet, and we don't have that address
                 * assigned for us.  We MUST silently ignore it.
                 * See RFC2461 7.2.3.
                 */
                goto freeit;
        }
        if ((((struct in6_ifaddr *)ifa)->ia6_flags & IN6_IFF_ANYCAST) != 0)
                dflags |= ND6_QUEUE_FLAG_ANYCAST;
        myaddr6 = *IFA_IN6(ifa);
        tentative = ((struct in6_ifaddr *)ifa)->ia6_flags & IN6_IFF_TENTATIVE;
        if (((struct in6_ifaddr *)ifa)->ia6_flags & IN6_IFF_DUPLICATED)
                goto freeit;

        if (lladdr && ((ifp->if_addrlen + 2 + 7) & ~7) != lladdrlen) {
                nd6log((LOG_INFO, "nd6_ns_input: lladdrlen mismatch for %s "
                    "(if %d, NS packet %d)\n",
                    ip6_sprintf(ip6bufs, &taddr6),
                    ifp->if_addrlen, lladdrlen - 2));
                goto bad;
        }

        if (IN6_ARE_ADDR_EQUAL(&myaddr6, &saddr6)) {
                nd6log((LOG_INFO, "nd6_ns_input: duplicate IP6 address %s\n",
                    ip6_sprintf(ip6bufs, &saddr6)));
                goto freeit;
        }

        /*
         * We have neighbor solicitation packet, with target address equals to
         * one of my tentative address.
         *
         * src addr     how to process?
         * ---          ---
         * multicast    of course, invalid (rejected in ip6_input)
         * unicast      somebody is doing address resolution -> ignore
         * unspec       dup address detection
         *
         * The processing is defined in RFC 2462.
         */
        if (tentative) {
                /*
                 * If source address is unspecified address, it is for
                 * duplicate address detection.
                 *
                 * If not, the packet is for addess resolution;
                 * silently ignore it.
                 */
                if (IN6_IS_ADDR_UNSPECIFIED(&saddr6))
                        nd6_dad_ns_input(ifa, ndopts.nd_opts_nonce);

                goto freeit;
        }

        /*
         * If the Target Address is either an anycast address or a unicast
         * address for which the node is providing proxy service, or the Target
         * Link-Layer Address option is not included, the Override flag SHOULD
         * be set to zero.  Otherwise, the Override flag SHOULD be set to one.
         */
        if (dflags == 0 && (tlladdr & ND6_NA_OPT_LLA) != 0)
                rflag |= ND_NA_FLAG_OVERRIDE;
        /*
         * If the source address is unspecified address, entries must not
         * be created or updated.
         * It looks that sender is performing DAD. nd6_na_output() will
         * send NA toward all-node multicast address, to tell the sender
         * that I'm using the address.
         * S bit ("solicited") must be zero.
         */
        if (!IN6_IS_ADDR_UNSPECIFIED(&saddr6)) {
                nd6_cache_lladdr(ifp, &saddr6, lladdr, lladdrlen,
                    ND_NEIGHBOR_SOLICIT, 0);
                rflag |= ND_NA_FLAG_SOLICITED;
        }

        /*
         * RFC 4861, anycast or proxy NA sent in response to a NS SHOULD
         * be delayed by a random time between 0 and MAX_ANYCAST_DELAY_TIME
         * to reduce the probability of network congestion.
         */
        if (dflags == 0)
                nd6_na_output_fib(ifp, &saddr6, &taddr6, rflag, tlladdr, NULL, M_GETFIB(m));
        else
                nd6_queue_add(ifa, &saddr6, &taddr6, &proxydl, arc4random() %
                    (MAX_ANYCAST_DELAY_TIME * hz), dflags);
 freeit:
        if (ifa != NULL)
                ifa_free(ifa);
        m_freem(m);
        return;

 bad:
        nd6log((LOG_ERR, "nd6_ns_input: src=%s\n",
                ip6_sprintf(ip6bufs, &saddr6)));
        nd6log((LOG_ERR, "nd6_ns_input: dst=%s\n",
                ip6_sprintf(ip6bufs, &daddr6)));
        nd6log((LOG_ERR, "nd6_ns_input: tgt=%s\n",
                ip6_sprintf(ip6bufs, &taddr6)));
 bads:
        ICMP6STAT_INC(icp6s_badns);
        if (ifa != NULL)
                ifa_free(ifa);
        m_freem(m);
}

static struct ifaddr *
nd6_proxy_fill_sdl(struct ifnet *ifp, const struct in6_addr *taddr6,
    struct sockaddr_dl *sdl)
{
        struct ifaddr *ifa;
        struct llentry *ln;

        ifa = NULL;
        ln = nd6_lookup(taddr6, LLE_SF(AF_INET6, 0), ifp);
        if (ln == NULL)
                return (ifa);
        if ((ln->la_flags & (LLE_PUB | LLE_VALID)) == (LLE_PUB | LLE_VALID)) {
                link_init_sdl(ifp, (struct sockaddr *)sdl, ifp->if_type);
                sdl->sdl_alen = ifp->if_addrlen;
                bcopy(ln->ll_addr, &sdl->sdl_data, ifp->if_addrlen);
                LLE_RUNLOCK(ln);
                ifa = (struct ifaddr *)in6ifa_ifpforlinklocal(ifp,
                    IN6_IFF_NOTREADY|IN6_IFF_ANYCAST);
        } else
                LLE_RUNLOCK(ln);

        return (ifa);
}

/*
 * Output a Neighbor Solicitation Message. Caller specifies:
 *      - ICMP6 header source IP6 address
 *      - ND6 header target IP6 address
 *      - ND6 header source datalink address
 *
 * Based on RFC 2461
 * Based on RFC 2462 (duplicate address detection)
 *
 *    ln - for source address determination
 * nonce - If non-NULL, NS is used for duplicate address detection and
 *         the value (length is ND_OPT_NONCE_LEN) is used as a random nonce.
 */
static void
nd6_ns_output_fib(struct ifnet *ifp, const struct in6_addr *saddr6,
    const struct in6_addr *daddr6, const struct in6_addr *taddr6,
    uint8_t *nonce, u_int fibnum)
{
        struct mbuf *m;
        struct m_tag *mtag;
        struct ip6_hdr *ip6;
        struct nd_neighbor_solicit *nd_ns;
        struct ip6_moptions im6o;
        int icmp6len;
        int maxlen;

        NET_EPOCH_ASSERT();

        if (IN6_IS_ADDR_MULTICAST(taddr6))
                return;

        /* estimate the size of message */
        maxlen = sizeof(*ip6) + sizeof(*nd_ns);
        maxlen += (sizeof(struct nd_opt_hdr) + ifp->if_addrlen + 7) & ~7;
        KASSERT(max_linkhdr + maxlen <= MCLBYTES, (
            "%s: max_linkhdr + maxlen > MCLBYTES (%d + %d > %d)",
            __func__, max_linkhdr, maxlen, MCLBYTES));

        if (max_linkhdr + maxlen > MHLEN)
                m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
        else
                m = m_gethdr(M_NOWAIT, MT_DATA);
        if (m == NULL)
                return;
        M_SETFIB(m, fibnum);

        icmp6len = sizeof(*nd_ns);
        m->m_pkthdr.len = m->m_len = sizeof(*ip6) + icmp6len;
        m->m_data += max_linkhdr;       /* or M_ALIGN() equivalent? */

        /* fill neighbor solicitation packet */
        ip6 = mtod(m, struct ip6_hdr *);
        ip6->ip6_flow = 0;
        ip6->ip6_vfc &= ~IPV6_VERSION_MASK;
        ip6->ip6_vfc |= IPV6_VERSION;
        /* ip6->ip6_plen will be set later */
        ip6->ip6_nxt = IPPROTO_ICMPV6;
        ip6->ip6_hlim = 255;
        if (daddr6)
                ip6->ip6_dst = *daddr6;
        else {
                ip6->ip6_dst.s6_addr16[0] = IPV6_ADDR_INT16_MLL;
                ip6->ip6_dst.s6_addr16[1] = 0;
                ip6->ip6_dst.s6_addr32[1] = 0;
                ip6->ip6_dst.s6_addr32[2] = IPV6_ADDR_INT32_ONE;
                ip6->ip6_dst.s6_addr32[3] = taddr6->s6_addr32[3];
                ip6->ip6_dst.s6_addr8[12] = 0xff;
                if (in6_setscope(&ip6->ip6_dst, ifp, NULL) != 0)
                        goto bad;
        }
        if (IN6_IS_ADDR_MULTICAST(&ip6->ip6_dst)) {
                m->m_flags |= M_MCAST;
                im6o.im6o_multicast_ifp = ifp;
                im6o.im6o_multicast_hlim = 255;
                im6o.im6o_multicast_loop = 0;
        }
        if (nonce == NULL) {
                char ip6buf[INET6_ADDRSTRLEN];
                struct ifaddr *ifa = NULL;

                /*
                 * RFC2461 7.2.2:
                 * "If the source address of the packet prompting the
                 * solicitation is the same as one of the addresses assigned
                 * to the outgoing interface, that address SHOULD be placed
                 * in the IP Source Address of the outgoing solicitation.
                 * Otherwise, any one of the addresses assigned to the
                 * interface should be used."
                 *
                 * We use the source address for the prompting packet
                 * (saddr6), if saddr6 belongs to the outgoing interface.
                 * Otherwise, we perform the source address selection as usual.
                 */
                if (saddr6 != NULL)
                        ifa = (struct ifaddr *)in6ifa_ifpwithaddr(ifp, saddr6);
                if (ifa == NULL) {
                        int error;

                        error = in6_selectsrc_nbr(fibnum, &ip6->ip6_dst, &im6o,
                            ifp, &ip6->ip6_src);
                        if (error) {
                                nd6log((LOG_DEBUG, "%s: source can't be "
                                    "determined: dst=%s, error=%d\n", __func__,
                                    ip6_sprintf(ip6buf, &ip6->ip6_dst),
                                    error));
                                goto bad;
                        }
                } else
                        ip6->ip6_src = *saddr6;

                if (ifp->if_carp != NULL) {
                        /*
                         * Check that selected source address belongs to
                         * CARP addresses.
                         */
                        if (ifa == NULL)
                                ifa = (struct ifaddr *)in6ifa_ifpwithaddr(ifp,
                                    &ip6->ip6_src);
                        /*
                         * Do not send NS for CARP address if we are not
                         * the CARP master.
                         */
                        if (ifa != NULL && ifa->ifa_carp != NULL &&
                            !(*carp_master_p)(ifa)) {
                                nd6log((LOG_DEBUG,
                                    "nd6_ns_output: NS from BACKUP CARP address %s\n",
                                    ip6_sprintf(ip6buf, &ip6->ip6_src)));
                                ifa_free(ifa);
                                goto bad;
                        }
                }
                if (ifa != NULL)
                        ifa_free(ifa);
        } else {
                /*
                 * Source address for DAD packet must always be IPv6
                 * unspecified address. (0::0)
                 * We actually don't have to 0-clear the address (we did it
                 * above), but we do so here explicitly to make the intention
                 * clearer.
                 */
                bzero(&ip6->ip6_src, sizeof(ip6->ip6_src));
        }
        nd_ns = (struct nd_neighbor_solicit *)(ip6 + 1);
        nd_ns->nd_ns_type = ND_NEIGHBOR_SOLICIT;
        nd_ns->nd_ns_code = 0;
        nd_ns->nd_ns_reserved = 0;
        nd_ns->nd_ns_target = *taddr6;
        in6_clearscope(&nd_ns->nd_ns_target); /* XXX */

        /*
         * Add source link-layer address option.
         *
         *                              spec            implementation
         *                              ---             ---
         * DAD packet                   MUST NOT        do not add the option
         * there's no link layer address:
         *                              impossible      do not add the option
         * there's link layer address:
         *      Multicast NS            MUST add one    add the option
         *      Unicast NS              SHOULD add one  add the option
         */
        if (nonce == NULL) {
                struct nd_opt_hdr *nd_opt;
                char *mac;
                int optlen;

                mac = NULL;
                if (ifp->if_carp)
                        mac = (*carp_macmatch6_p)(ifp, m, &ip6->ip6_src);
                if (mac == NULL)
                        mac = nd6_ifptomac(ifp);

                if (mac != NULL) {
                        nd_opt = (struct nd_opt_hdr *)(nd_ns + 1);
                        optlen = sizeof(struct nd_opt_hdr) + ifp->if_addrlen;
                        /* 8 byte alignments... */
                        optlen = (optlen + 7) & ~7;
                        m->m_pkthdr.len += optlen;
                        m->m_len += optlen;
                        icmp6len += optlen;
                        bzero(nd_opt, optlen);
                        nd_opt->nd_opt_type = ND_OPT_SOURCE_LINKADDR;
                        nd_opt->nd_opt_len = optlen >> 3;
                        bcopy(mac, nd_opt + 1, ifp->if_addrlen);
                }
        }
        /*
         * Add a Nonce option (RFC 3971) to detect looped back NS messages.
         * This behavior is documented as Enhanced Duplicate Address
         * Detection in RFC 7527.
         * net.inet6.ip6.dad_enhanced=0 disables this.
         */
        if (V_dad_enhanced != 0 && nonce != NULL) {
                int optlen = sizeof(struct nd_opt_hdr) + ND_OPT_NONCE_LEN;
                struct nd_opt_hdr *nd_opt = (struct nd_opt_hdr *)(nd_ns + 1);
                /* 8-byte alignment is required. */
                optlen = (optlen + 7) & ~7;

                m->m_pkthdr.len += optlen;
                m->m_len += optlen;
                icmp6len += optlen;
                bzero((caddr_t)nd_opt, optlen);
                nd_opt->nd_opt_type = ND_OPT_NONCE;
                nd_opt->nd_opt_len = optlen >> 3;
                bcopy(nonce, (caddr_t)(nd_opt + 1), ND_OPT_NONCE_LEN);
        }
        ip6->ip6_plen = htons((u_short)icmp6len);
        nd_ns->nd_ns_cksum = 0;
        nd_ns->nd_ns_cksum =
            in6_cksum(m, IPPROTO_ICMPV6, sizeof(*ip6), icmp6len);

        if (send_sendso_input_hook != NULL) {
                mtag = m_tag_get(PACKET_TAG_ND_OUTGOING,
                        sizeof(unsigned short), M_NOWAIT);
                if (mtag == NULL)
                        goto bad;
                *(unsigned short *)(mtag + 1) = nd_ns->nd_ns_type;
                m_tag_prepend(m, mtag);
        }

        ip6_output(m, NULL, NULL, (nonce != NULL) ? IPV6_UNSPECSRC : 0,
            &im6o, NULL, NULL);
        icmp6_ifstat_inc(ifp, ifs6_out_msg);
        icmp6_ifstat_inc(ifp, ifs6_out_neighborsolicit);
        ICMP6STAT_INC2(icp6s_outhist, ND_NEIGHBOR_SOLICIT);

        return;

  bad:
        m_freem(m);
}

#ifndef BURN_BRIDGES
void
nd6_ns_output(struct ifnet *ifp, const struct in6_addr *saddr6,
    const struct in6_addr *daddr6, const struct in6_addr *taddr6,uint8_t *nonce)
{

        nd6_ns_output_fib(ifp, saddr6, daddr6, taddr6, nonce, RT_DEFAULT_FIB);
}
#endif
/*
 * Neighbor advertisement input handling.
 *
 * Based on RFC 2461
 * Based on RFC 2462 (duplicate address detection)
 */
void
nd6_na_input(struct mbuf *m, int off, int icmp6len)
{
        struct ifnet *ifp;
        struct ip6_hdr *ip6;
        struct ifaddr *ifa;
        struct llentry *ln;
        struct mbuf *chain;
        struct nd_neighbor_advert *nd_na;
        struct in6_addr daddr6, taddr6;
        union nd_opts ndopts;
        u_char linkhdr[LLE_MAX_LINKHDR];
        char ip6bufs[INET6_ADDRSTRLEN], ip6bufd[INET6_ADDRSTRLEN];
        char *lladdr;
        size_t linkhdrsize;
        int flags, is_override, is_router, is_solicited;
        int lladdr_off, lladdrlen, checklink;
        bool flush_holdchain = false;

        NET_EPOCH_ASSERT();

        chain = NULL;
        ln = NULL;
        checklink = 0;

        /* RFC 6980: Nodes MUST silently ignore fragments */
        if(m->m_flags & M_FRAGMENTED)
                goto freeit;

        ifp = m->m_pkthdr.rcvif;
        ip6 = mtod(m, struct ip6_hdr *);
        if (__predict_false(ip6->ip6_hlim != 255)) {
                ICMP6STAT_INC(icp6s_invlhlim);
                nd6log((LOG_ERR,
                    "nd6_na_input: invalid hlim (%d) from %s to %s on %s\n",
                    ip6->ip6_hlim, ip6_sprintf(ip6bufs, &ip6->ip6_src),
                    ip6_sprintf(ip6bufd, &ip6->ip6_dst), if_name(ifp)));
                goto bad;
        }

        if (m->m_len < off + icmp6len) {
                m = m_pullup(m, off + icmp6len);
                if (m == NULL) {
                        IP6STAT_INC(ip6s_exthdrtoolong);
                        return;
                }
        }
        ip6 = mtod(m, struct ip6_hdr *);
        nd_na = (struct nd_neighbor_advert *)((caddr_t)ip6 + off);

        flags = nd_na->nd_na_flags_reserved;
        is_router = ((flags & ND_NA_FLAG_ROUTER) != 0);
        is_solicited = ((flags & ND_NA_FLAG_SOLICITED) != 0);
        is_override = ((flags & ND_NA_FLAG_OVERRIDE) != 0);

        taddr6 = nd_na->nd_na_target;
        if (in6_setscope(&taddr6, ifp, NULL))
                goto bad;       /* XXX: impossible */

        if (IN6_IS_ADDR_MULTICAST(&taddr6)) {
                nd6log((LOG_ERR,
                    "nd6_na_input: invalid target address %s\n",
                    ip6_sprintf(ip6bufs, &taddr6)));
                goto bad;
        }

        daddr6 = ip6->ip6_dst;
        if (IN6_IS_ADDR_MULTICAST(&daddr6))
                if (is_solicited) {
                        nd6log((LOG_ERR,
                            "nd6_na_input: a solicited adv is multicasted\n"));
                        goto bad;
                }

        icmp6len -= sizeof(*nd_na);
        nd6_option_init(nd_na + 1, icmp6len, &ndopts);
        if (nd6_options(&ndopts) < 0) {
                nd6log((LOG_INFO,
                    "nd6_na_input: invalid ND option, ignored\n"));
                /* nd6_options have incremented stats */
                goto freeit;
        }

        lladdr = NULL;
        lladdrlen = 0;
        if (ndopts.nd_opts_tgt_lladdr) {
                lladdr = (char *)(ndopts.nd_opts_tgt_lladdr + 1);
                lladdrlen = ndopts.nd_opts_tgt_lladdr->nd_opt_len << 3;
        }

        ifa = (struct ifaddr *)in6ifa_ifpwithaddr(ifp, &taddr6);
        if (ifa != NULL && ifa->ifa_carp != NULL) {
                /*
                 * Silently ignore NAs for CARP addresses if we are not
                 * the CARP master.
                 */
                if (!(*carp_master_p)(ifa)) {
                        nd6log((LOG_DEBUG,
                            "nd6_na_input: NA for BACKUP CARP address %s\n",
                            ip6_sprintf(ip6bufs, &taddr6)));
                        ifa_free(ifa);
                        goto freeit;
                }
        }
        /*
         * Target address matches one of my interface address.
         *
         * If my address is tentative, this means that there's somebody
         * already using the same address as mine.  This indicates DAD failure.
         * This is defined in RFC 2462.
         *
         * Otherwise, process as defined in RFC 2461.
         */
        if (ifa
         && (((struct in6_ifaddr *)ifa)->ia6_flags & IN6_IFF_TENTATIVE)) {
                nd6_dad_na_input(ifa);
                ifa_free(ifa);
                goto freeit;
        }

        /* Just for safety, maybe unnecessary. */
        if (ifa) {
                ifa_free(ifa);
                log(LOG_ERR,
                    "nd6_na_input: duplicate IP6 address %s\n",
                    ip6_sprintf(ip6bufs, &taddr6));
                goto freeit;
        }

        if (lladdr && ((ifp->if_addrlen + 2 + 7) & ~7) != lladdrlen) {
                nd6log((LOG_INFO, "nd6_na_input: lladdrlen mismatch for %s "
                    "(if %d, NA packet %d)\n", ip6_sprintf(ip6bufs, &taddr6),
                    ifp->if_addrlen, lladdrlen - 2));
                goto bad;
        }

        /*
         * If no neighbor cache entry is found, NA SHOULD silently be
         * discarded.
         */
        ln = nd6_lookup(&taddr6, LLE_SF(AF_INET6, LLE_EXCLUSIVE), ifp);
        if (ln == NULL) {
                goto freeit;
        }

        /*
         * Do not try to override static entry.
         */
        if (ln->la_flags & LLE_STATIC)
                goto freeit;

        if (ln->ln_state == ND6_LLINFO_INCOMPLETE) {
                /*
                 * If the link-layer has address, and no lladdr option came,
                 * discard the packet.
                 */
                if (ifp->if_addrlen && lladdr == NULL) {
                        goto freeit;
                }

                /*
                 * Record link-layer address, and update the state.
                 */
                if (!nd6_try_set_entry_addr(ifp, ln, lladdr))
                        goto freeit;

                flush_holdchain = true;
                if (is_solicited)
                        nd6_llinfo_setstate(ln, ND6_LLINFO_REACHABLE);
                else
                        nd6_llinfo_setstate(ln, ND6_LLINFO_STALE);
                EVENTHANDLER_INVOKE(lle_event, ln, LLENTRY_RESOLVED);
                if ((ln->ln_router = is_router) != 0) {
                        /*
                         * This means a router's state has changed from
                         * non-reachable to probably reachable, and might
                         * affect the status of associated prefixes..
                         */
                        checklink = 1;
                }
        } else {
                int llchange;

                /*
                 * Check if the link-layer address has changed or not.
                 */
                if (lladdr == NULL)
                        llchange = 0;
                else {
                        if (ln->la_flags & LLE_VALID) {
                                if (bcmp(lladdr, ln->ll_addr, ifp->if_addrlen))
                                        llchange = 1;
                                else
                                        llchange = 0;
                        } else
                                llchange = 1;
                }

                /*
                 * This is VERY complex.  Look at it with care.
                 *
                 * override solicit lladdr llchange     action
                 *                                      (L: record lladdr)
                 *
                 *      0       0       n       --      (2c)
                 *      0       0       y       n       (2b) L
                 *      0       0       y       y       (1)    REACHABLE->STALE
                 *      0       1       n       --      (2c)   *->REACHABLE
                 *      0       1       y       n       (2b) L *->REACHABLE
                 *      0       1       y       y       (1)    REACHABLE->STALE
                 *      1       0       n       --      (2a)
                 *      1       0       y       n       (2a) L
                 *      1       0       y       y       (2a) L *->STALE
                 *      1       1       n       --      (2a)   *->REACHABLE
                 *      1       1       y       n       (2a) L *->REACHABLE
                 *      1       1       y       y       (2a) L *->REACHABLE
                 */
                if (!is_override && (lladdr != NULL && llchange)) {  /* (1) */
                        /*
                         * If state is REACHABLE, make it STALE.
                         * no other updates should be done.
                         */
                        if (ln->ln_state == ND6_LLINFO_REACHABLE)
                                nd6_llinfo_setstate(ln, ND6_LLINFO_STALE);
                        goto freeit;
                } else if (is_override                             /* (2a) */
                        || (!is_override && (lladdr != NULL && !llchange)) /* (2b) */
                        || lladdr == NULL) {                       /* (2c) */
                        /*
                         * Update link-local address, if any.
                         */
                        if (lladdr != NULL) {
                                linkhdrsize = sizeof(linkhdr);
                                if (lltable_calc_llheader(ifp, AF_INET6, lladdr,
                                    linkhdr, &linkhdrsize, &lladdr_off) != 0)
                                        goto freeit;
                                if (lltable_try_set_entry_addr(ifp, ln, linkhdr,
                                    linkhdrsize, lladdr_off) == 0)
                                        goto freeit;
                                EVENTHANDLER_INVOKE(lle_event, ln,
                                    LLENTRY_RESOLVED);
                        }

                        /*
                         * If solicited, make the state REACHABLE.
                         * If not solicited and the link-layer address was
                         * changed, make it STALE.
                         */
                        if (is_solicited)
                                nd6_llinfo_setstate(ln, ND6_LLINFO_REACHABLE);
                        else {
                                if (lladdr != NULL && llchange)
                                        nd6_llinfo_setstate(ln, ND6_LLINFO_STALE);
                        }
                }

                if (ln->ln_router && !is_router) {
                        /*
                         * The peer dropped the router flag.
                         * Remove the sender from the Default Router List and
                         * update the Destination Cache entries.
                         */
                        struct ifnet *nd6_ifp;

                        nd6_ifp = lltable_get_ifp(ln->lle_tbl);
                        if (!defrouter_remove(&ln->r_l3addr.addr6, nd6_ifp) &&
                            (nd6_ifp->if_inet6->nd_flags &
                             ND6_IFF_ACCEPT_RTADV) != 0)
                                /*
                                 * Even if the neighbor is not in the default
                                 * router list, the neighbor may be used as a
                                 * next hop for some destinations (e.g. redirect
                                 * case). So we must call rt6_flush explicitly.
                                 */
                                rt6_flush(&ip6->ip6_src, ifp);
                }
                ln->ln_router = is_router;
        }
        /* XXX - QL
         *  Does this matter?
         *  rt->rt_flags &= ~RTF_REJECT;
         */
        ln->la_asked = 0;
        if (ln->la_hold != NULL)
                chain = nd6_grab_holdchain(ln);
 freeit:
        if (ln != NULL)
                LLE_WUNLOCK(ln);

        if (chain != NULL)
                nd6_flush_holdchain(ifp, ln, chain);
        if (flush_holdchain)
                nd6_flush_children_holdchain(ifp, ln);

        if (checklink)
                pfxlist_onlink_check();

        m_freem(m);
        return;

 bad:
        if (ln != NULL)
                LLE_WUNLOCK(ln);

        ICMP6STAT_INC(icp6s_badna);
        m_freem(m);
}

/*
 * Neighbor advertisement output handling.
 *
 * Based on RFC 2461
 *
 * tlladdr:
 * - 0x01 if include target link-layer address
 * - 0x02 if target address is CARP MASTER
 * sdl0 - sockaddr_dl (= proxy NA) or NULL
 */
static void
nd6_na_output_fib(struct ifnet *ifp, const struct in6_addr *daddr6_0,
    const struct in6_addr *taddr6, u_long flags, int tlladdr,
    struct sockaddr *sdl0, u_int fibnum)
{
        struct mbuf *m;
        struct m_tag *mtag;
        struct ip6_hdr *ip6;
        struct nd_neighbor_advert *nd_na;
        struct ip6_moptions im6o;
        struct in6_addr daddr6;

        NET_EPOCH_ASSERT();

        int icmp6len, maxlen, error;
        caddr_t mac = NULL;

        daddr6 = *daddr6_0;     /* make a local copy for modification */

        /* estimate the size of message */
        maxlen = sizeof(*ip6) + sizeof(*nd_na);
        maxlen += (sizeof(struct nd_opt_hdr) + ifp->if_addrlen + 7) & ~7;
        KASSERT(max_linkhdr + maxlen <= MCLBYTES, (
            "%s: max_linkhdr + maxlen > MCLBYTES (%d + %d > %d)",
            __func__, max_linkhdr, maxlen, MCLBYTES));

        if (max_linkhdr + maxlen > MHLEN)
                m = m_getcl(M_NOWAIT, MT_DATA, M_PKTHDR);
        else
                m = m_gethdr(M_NOWAIT, MT_DATA);
        if (m == NULL)
                return;
        M_SETFIB(m, fibnum);

        icmp6len = sizeof(*nd_na);
        m->m_pkthdr.len = m->m_len = sizeof(struct ip6_hdr) + icmp6len;
        m->m_data += max_linkhdr;       /* or M_ALIGN() equivalent? */

        /* fill neighbor advertisement packet */
        ip6 = mtod(m, struct ip6_hdr *);
        ip6->ip6_flow = 0;
        ip6->ip6_vfc &= ~IPV6_VERSION_MASK;
        ip6->ip6_vfc |= IPV6_VERSION;
        ip6->ip6_nxt = IPPROTO_ICMPV6;
        ip6->ip6_hlim = 255;

        if (IN6_IS_ADDR_UNSPECIFIED(&daddr6)) {
                /* reply to DAD */
                daddr6 = in6addr_linklocal_allnodes;
                if (in6_setscope(&daddr6, ifp, NULL))
                        goto bad;

                flags &= ~ND_NA_FLAG_SOLICITED;
        }
        if (IN6_IS_ADDR_MULTICAST(&daddr6)) {
                m->m_flags |= M_MCAST;
                im6o.im6o_multicast_ifp = ifp;
                im6o.im6o_multicast_hlim = 255;
                im6o.im6o_multicast_loop = 0;
        }

        ip6->ip6_dst = daddr6;
        error = in6_selectsrc_nbr(fibnum, &daddr6, &im6o, ifp, &ip6->ip6_src);
        if (error) {
                char ip6buf[INET6_ADDRSTRLEN];
                nd6log((LOG_DEBUG, "nd6_na_output: source can't be "
                    "determined: dst=%s, error=%d\n",
                    ip6_sprintf(ip6buf, &daddr6), error));
                goto bad;
        }
        nd_na = (struct nd_neighbor_advert *)(ip6 + 1);
        nd_na->nd_na_type = ND_NEIGHBOR_ADVERT;
        nd_na->nd_na_code = 0;
        nd_na->nd_na_target = *taddr6;
        in6_clearscope(&nd_na->nd_na_target); /* XXX */

        /*
         * If we respond from CARP address, we need to prepare mac address
         * for carp_output().
         */
        if (ifp->if_carp && (tlladdr & ND6_NA_CARP_MASTER))
                mac = (*carp_macmatch6_p)(ifp, m, taddr6);
        /*
         * "tlladdr" indicates NS's condition for adding tlladdr or not.
         * see nd6_ns_input() for details.
         * Basically, if NS packet is sent to unicast/anycast addr,
         * target lladdr option SHOULD NOT be included.
         */
        if (tlladdr & ND6_NA_OPT_LLA) {
                /*
                 * sdl0 != NULL indicates proxy NA.  If we do proxy, use
                 * lladdr in sdl0.  If we are not proxying (sending NA for
                 * my address) use lladdr configured for the interface.
                 */
                if (sdl0 == NULL) {
                        if (mac == NULL)
                                mac = nd6_ifptomac(ifp);
                } else if (sdl0->sa_family == AF_LINK) {
                        struct sockaddr_dl *sdl;
                        sdl = (struct sockaddr_dl *)sdl0;
                        if (sdl->sdl_alen == ifp->if_addrlen)
                                mac = LLADDR(sdl);
                }
        }
        if ((tlladdr & ND6_NA_OPT_LLA) && mac != NULL) {
                int optlen = sizeof(struct nd_opt_hdr) + ifp->if_addrlen;
                struct nd_opt_hdr *nd_opt = (struct nd_opt_hdr *)(nd_na + 1);

                /* roundup to 8 bytes alignment! */
                optlen = (optlen + 7) & ~7;

                m->m_pkthdr.len += optlen;
                m->m_len += optlen;
                icmp6len += optlen;
                bzero((caddr_t)nd_opt, optlen);
                nd_opt->nd_opt_type = ND_OPT_TARGET_LINKADDR;
                nd_opt->nd_opt_len = optlen >> 3;
                bcopy(mac, (caddr_t)(nd_opt + 1), ifp->if_addrlen);
        } else
                flags &= ~ND_NA_FLAG_OVERRIDE;

        ip6->ip6_plen = htons((u_short)icmp6len);
        nd_na->nd_na_flags_reserved = flags;
        nd_na->nd_na_cksum = 0;
        nd_na->nd_na_cksum =
            in6_cksum(m, IPPROTO_ICMPV6, sizeof(struct ip6_hdr), icmp6len);

        if (send_sendso_input_hook != NULL) {
                mtag = m_tag_get(PACKET_TAG_ND_OUTGOING,
                    sizeof(unsigned short), M_NOWAIT);
                if (mtag == NULL)
                        goto bad;
                *(unsigned short *)(mtag + 1) = nd_na->nd_na_type;
                m_tag_prepend(m, mtag);
        }

        ip6_output(m, NULL, NULL, 0, &im6o, NULL, NULL);
        icmp6_ifstat_inc(ifp, ifs6_out_msg);
        icmp6_ifstat_inc(ifp, ifs6_out_neighboradvert);
        ICMP6STAT_INC2(icp6s_outhist, ND_NEIGHBOR_ADVERT);

        return;

  bad:
        m_freem(m);
}

#ifndef BURN_BRIDGES
void
nd6_na_output(struct ifnet *ifp, const struct in6_addr *daddr6_0,
    const struct in6_addr *taddr6, u_long flags, int tlladdr,
    struct sockaddr *sdl0)
{

        nd6_na_output_fib(ifp, daddr6_0, taddr6, flags, tlladdr, sdl0,
            RT_DEFAULT_FIB);
}
#endif

caddr_t
nd6_ifptomac(struct ifnet *ifp)
{
        switch (ifp->if_type) {
        case IFT_ETHER:
        case IFT_IEEE1394:
        case IFT_L2VLAN:
        case IFT_INFINIBAND:
        case IFT_BRIDGE:
                return IF_LLADDR(ifp);
        default:
                return NULL;
        }
}

struct dadq {
        TAILQ_ENTRY(dadq) dad_list;
        struct ifaddr *dad_ifa;
        int dad_count;          /* max NS to send */
        int dad_ns_tcount;      /* # of trials to send NS */
        int dad_ns_ocount;      /* NS sent so far */
        int dad_ns_icount;
        int dad_na_icount;
        int dad_ns_lcount;      /* looped back NS */
        int dad_loopbackprobe;  /* probing state for loopback detection */
        struct callout dad_timer_ch;
        struct vnet *dad_vnet;
        u_int dad_refcnt;
#define ND_OPT_NONCE_LEN32 \
                ((ND_OPT_NONCE_LEN + sizeof(uint32_t) - 1)/sizeof(uint32_t))
        uint32_t dad_nonce[ND_OPT_NONCE_LEN32];
        bool dad_ondadq;        /* on dadq? Protected by DADQ_WLOCK. */
};

VNET_DEFINE_STATIC(TAILQ_HEAD(, dadq), dadq);
VNET_DEFINE_STATIC(struct rwlock, dad_rwlock);
#define V_dadq                  VNET(dadq)
#define V_dad_rwlock            VNET(dad_rwlock)

#define DADQ_LOCKPTR()          (&V_dad_rwlock)
#define DADQ_LOCK_INIT()        rw_init(DADQ_LOCKPTR(), "nd6 DAD queue")
#define DADQ_RLOCK()            rw_rlock(DADQ_LOCKPTR())
#define DADQ_RUNLOCK()          rw_runlock(DADQ_LOCKPTR())
#define DADQ_WLOCK()            rw_wlock(DADQ_LOCKPTR())
#define DADQ_WUNLOCK()          rw_wunlock(DADQ_LOCKPTR())

#define DADQ_LOCK_ASSERT()      rw_assert(DADQ_LOCKPTR(), RA_LOCKED);
#define DADQ_RLOCK_ASSERT()     rw_assert(DADQ_LOCKPTR(), RA_RLOCKED);
#define DADQ_WLOCK_ASSERT()     rw_assert(DADQ_LOCKPTR(), RA_WLOCKED);

static void
nd6_dad_add(struct dadq *dp)
{
        DADQ_WLOCK_ASSERT();

        TAILQ_INSERT_TAIL(&V_dadq, dp, dad_list);
        dp->dad_ondadq = true;
}

static void
nd6_dad_del(struct dadq *dp)
{
        DADQ_WLOCK_ASSERT();

        if (dp->dad_ondadq) {
                /*
                 * Remove dp from the dadq and release the dadq's
                 * reference.
                 */
                TAILQ_REMOVE(&V_dadq, dp, dad_list);
                dp->dad_ondadq = false;
                nd6_dad_rele(dp);
        }
}

static struct dadq *
nd6_dad_find(struct ifaddr *ifa, struct nd_opt_nonce *n)
{
        struct dadq *dp;

        DADQ_LOCK_ASSERT();

        TAILQ_FOREACH(dp, &V_dadq, dad_list) {
                if (dp->dad_ifa != ifa)
                        continue;

                /*
                 * Skip if the nonce matches the received one.
                 * +2 in the length is required because of type and
                 * length fields are included in a header.
                 */
                if (n != NULL &&
                    n->nd_opt_nonce_len == (ND_OPT_NONCE_LEN + 2) / 8 &&
                    memcmp(&n->nd_opt_nonce[0], &dp->dad_nonce[0],
                    ND_OPT_NONCE_LEN) == 0) {
                        dp->dad_ns_lcount++;
                        continue;
                }
                break;
        }

        return (dp);
}

static void
nd6_dad_starttimer(struct dadq *dp, int ticks)
{
        DADQ_WLOCK_ASSERT();

        callout_reset(&dp->dad_timer_ch, ticks, nd6_dad_timer, dp);
}

static void
nd6_dad_stoptimer(struct dadq *dp)
{
        callout_drain(&dp->dad_timer_ch);
}

static void
nd6_dad_rele(struct dadq *dp)
{
        if (refcount_release(&dp->dad_refcnt)) {
                KASSERT(!dp->dad_ondadq, ("dp %p still on DAD queue", dp));
                ifa_free(dp->dad_ifa);
                free(dp, M_IP6NDP);
        }
}

void
nd6_dad_init(void)
{
        DADQ_LOCK_INIT();
        TAILQ_INIT(&V_dadq);
}

/*
 * Start Duplicate Address Detection (DAD) for specified interface address.
 */
void
nd6_dad_start(struct ifaddr *ifa, int delay)
{
        struct in6_ifaddr *ia = (struct in6_ifaddr *)ifa;
        struct dadq *dp;
        char ip6buf[INET6_ADDRSTRLEN];

        KASSERT((ia->ia6_flags & IN6_IFF_TENTATIVE) != 0,
            ("starting DAD on non-tentative address %p", ifa));

        /*
         * If we don't need DAD, don't do it.
         * There are several cases:
         * - DAD is disabled globally or on the interface
         * - the interface address is anycast
         */
        if ((ia->ia6_flags & IN6_IFF_ANYCAST) != 0 ||
            V_ip6_dad_count == 0 ||
            (ifa->ifa_ifp->if_inet6->nd_flags & ND6_IFF_NO_DAD) != 0) {
                ia->ia6_flags &= ~IN6_IFF_TENTATIVE;
                return;
        }
        if ((ifa->ifa_ifp->if_flags & IFF_UP) == 0 ||
            (ifa->ifa_ifp->if_drv_flags & IFF_DRV_RUNNING) == 0 ||
            (ifa->ifa_ifp->if_inet6->nd_flags & ND6_IFF_IFDISABLED) != 0)
                return;

        DADQ_WLOCK();
        if ((dp = nd6_dad_find(ifa, NULL)) != NULL) {
                /*
                 * DAD is already in progress.  Let the existing entry
                 * finish it.
                 */
                DADQ_WUNLOCK();
                return;
        }

        dp = malloc(sizeof(*dp), M_IP6NDP, M_NOWAIT | M_ZERO);
        if (dp == NULL) {
                log(LOG_ERR, "nd6_dad_start: memory allocation failed for "
                        "%s(%s)\n",
                        ip6_sprintf(ip6buf, &ia->ia_addr.sin6_addr),
                        ifa->ifa_ifp ? if_name(ifa->ifa_ifp) : "???");
                return;
        }
        callout_init_rw(&dp->dad_timer_ch, DADQ_LOCKPTR(),
            CALLOUT_RETURNUNLOCKED);
#ifdef VIMAGE
        dp->dad_vnet = curvnet;
#endif
        nd6log((LOG_DEBUG, "%s: starting DAD for %s\n", if_name(ifa->ifa_ifp),
            ip6_sprintf(ip6buf, &ia->ia_addr.sin6_addr)));

        /*
         * Send NS packet for DAD, ip6_dad_count times.
         * Note that we must delay the first transmission, if this is the
         * first packet to be sent from the interface after interface
         * (re)initialization.
         */
        dp->dad_ifa = ifa;
        ifa_ref(dp->dad_ifa);
        dp->dad_count = V_ip6_dad_count;
        dp->dad_ns_icount = dp->dad_na_icount = 0;
        dp->dad_ns_ocount = dp->dad_ns_tcount = 0;
        dp->dad_ns_lcount = dp->dad_loopbackprobe = 0;

        /* Add this to the dadq and add a reference for the dadq. */
        refcount_init(&dp->dad_refcnt, 1);
        nd6_dad_add(dp);
        nd6_dad_starttimer(dp, delay);
        DADQ_WUNLOCK();
}

/*
 * terminate DAD unconditionally.  used for address removals.
 */
void
nd6_dad_stop(struct ifaddr *ifa)
{
        struct dadq *dp;

        DADQ_WLOCK();
        dp = nd6_dad_find(ifa, NULL);
        if (dp == NULL) {
                DADQ_WUNLOCK();
                /* DAD wasn't started yet */
                return;
        }

        /*
         * Acquire a temporary reference so that we can safely stop the callout.
         */
        (void)refcount_acquire(&dp->dad_refcnt);
        nd6_dad_del(dp);
        DADQ_WUNLOCK();

        nd6_dad_stoptimer(dp);
        nd6_dad_rele(dp);
}

static void
nd6_dad_timer(void *arg)
{
        struct dadq *dp = arg;
        struct ifaddr *ifa = dp->dad_ifa;
        struct ifnet *ifp = dp->dad_ifa->ifa_ifp;
        struct in6_ifaddr *ia = (struct in6_ifaddr *)ifa;
        char ip6buf[INET6_ADDRSTRLEN];
        struct epoch_tracker et;

        CURVNET_SET(dp->dad_vnet);
        KASSERT(ia != NULL, ("DAD entry %p with no address", dp));

        NET_EPOCH_ENTER(et);
        if (ifp->if_inet6->nd_flags & ND6_IFF_IFDISABLED) {
                /* Do not need DAD for ifdisabled interface. */
                log(LOG_ERR, "nd6_dad_timer: cancel DAD on %s because of "
                    "ND6_IFF_IFDISABLED.\n", ifp->if_xname);
                goto err;
        }
        if (ia->ia6_flags & IN6_IFF_DUPLICATED) {
                log(LOG_ERR, "nd6_dad_timer: called with duplicated address "
                        "%s(%s)\n",
                        ip6_sprintf(ip6buf, &ia->ia_addr.sin6_addr),
                        ifa->ifa_ifp ? if_name(ifa->ifa_ifp) : "???");
                goto err;
        }
        if ((ia->ia6_flags & IN6_IFF_TENTATIVE) == 0) {
                log(LOG_ERR, "nd6_dad_timer: called with non-tentative address "
                        "%s(%s)\n",
                        ip6_sprintf(ip6buf, &ia->ia_addr.sin6_addr),
                        ifa->ifa_ifp ? if_name(ifa->ifa_ifp) : "???");
                goto err;
        }

        /* Stop DAD if the interface is down even after dad_maxtry attempts. */
        if ((dp->dad_ns_tcount > V_dad_maxtry) &&
            (((ifp->if_flags & IFF_UP) == 0) ||
             ((ifp->if_drv_flags & IFF_DRV_RUNNING) == 0))) {
                nd6log((LOG_INFO, "%s: could not run DAD "
                    "because the interface was down or not running.\n",
                    if_name(ifa->ifa_ifp)));
                goto err;
        }

        /* Need more checks? */
        if (dp->dad_ns_ocount < dp->dad_count) {
                /*
                 * We have more NS to go.  Send NS packet for DAD.
                 */
                nd6_dad_starttimer(dp,
                    (long)ifa->ifa_ifp->if_inet6->nd_retrans * hz / 1000);
                nd6_dad_ns_output(dp);
                goto done;
        } else {
                /*
                 * We have transmitted sufficient number of DAD packets.
                 * See what we've got.
                 */
                if (dp->dad_ns_icount > 0 || dp->dad_na_icount > 0) {
                        /* We've seen NS or NA, means DAD has failed. */
                        nd6_dad_duplicated(ifa, dp);
                } else if (V_dad_enhanced != 0 &&
                    dp->dad_ns_lcount > 0 &&
                    dp->dad_ns_lcount > dp->dad_loopbackprobe) {
                        /*
                         * Sec. 4.1 in RFC 7527 requires transmission of
                         * additional probes until the loopback condition
                         * becomes clear when a looped back probe is detected.
                         */
                        log(LOG_ERR, "%s: a looped back NS message is "
                            "detected during DAD for %s.  "
                            "Another DAD probes are being sent.\n",
                            if_name(ifa->ifa_ifp),
                            ip6_sprintf(ip6buf, IFA_IN6(ifa)));
                        dp->dad_loopbackprobe = dp->dad_ns_lcount;
                        /*
                         * Send an NS immediately and increase dad_count by
                         * V_nd6_mmaxtries - 1.
                         */
                        dp->dad_count =
                            dp->dad_ns_ocount + V_nd6_mmaxtries - 1;
                        nd6_dad_starttimer(dp,
                            (long)ifa->ifa_ifp->if_inet6->nd_retrans * hz / 1000);
                        nd6_dad_ns_output(dp);
                        goto done;
                } else {
                        /*
                         * We are done with DAD.  No NA came, no NS came.
                         * No duplicate address found.  Check IFDISABLED flag
                         * again in case that it is changed between the
                         * beginning of this function and here.
                         *
                         * Reset DAD failures counter if using stable addresses.
                         */
                        if ((ifp->if_inet6->nd_flags & ND6_IFF_IFDISABLED) == 0) {
                                ia->ia6_flags &= ~IN6_IFF_TENTATIVE;
                                if ((ifp->if_inet6->nd_flags & ND6_IFF_STABLEADDR) && !(ia->ia6_flags & IN6_IFF_TEMPORARY))
                                        atomic_store_int(&DAD_FAILURES(ifp), 0);
                                /*
                                 * RFC 9131 Section 6.1.2: The first advertisement
                                 * SHOULD be sent as soon as an address changes the
                                 * state from tentative to preferred.
                                 */
                                nd6_grand_start(ifa, ND6_QUEUE_FLAG_NEWGUA);
                        }

                        nd6log((LOG_DEBUG,
                            "%s: DAD complete for %s - no duplicates found\n",
                            if_name(ifa->ifa_ifp),
                            ip6_sprintf(ip6buf, &ia->ia_addr.sin6_addr)));
                        if (dp->dad_ns_lcount > 0)
                                log(LOG_ERR, "%s: DAD completed while "
                                    "a looped back NS message is detected "
                                    "during DAD for %s.\n",
                                    if_name(ifa->ifa_ifp),
                                    ip6_sprintf(ip6buf, IFA_IN6(ifa)));
                }
        }
err:
        nd6_dad_del(dp);
        DADQ_WUNLOCK();
done:
        NET_EPOCH_EXIT(et);
        CURVNET_RESTORE();
}

static void
nd6_dad_duplicated(struct ifaddr *ifa, struct dadq *dp)
{
        struct in6_ifaddr *ia = (struct in6_ifaddr *)ifa;
        struct ifnet *ifp;
        char ip6buf[INET6_ADDRSTRLEN];

        ifp = ifa->ifa_ifp;

        log(LOG_ERR, "%s: DAD detected duplicate IPv6 address %s: "
            "NS in/out/loopback=%d/%d/%d, NA in=%d\n",
            if_name(ifp), ip6_sprintf(ip6buf, &ia->ia_addr.sin6_addr),
            dp->dad_ns_icount, dp->dad_ns_ocount, dp->dad_ns_lcount,
            dp->dad_na_icount);

        ia->ia6_flags &= ~IN6_IFF_TENTATIVE;
        ia->ia6_flags |= IN6_IFF_DUPLICATED;

        log(LOG_ERR, "%s: DAD complete for %s - duplicate found\n",
            if_name(ifp), ip6_sprintf(ip6buf, &ia->ia_addr.sin6_addr));

        /*
         * For RFC 7217 stable addresses, increment failure counter here if we still have retries.
         * More addresses will be generated as long as retries are not exhausted.
         */
        if ((ifp->if_inet6->nd_flags & ND6_IFF_STABLEADDR) && !(ia->ia6_flags & IN6_IFF_TEMPORARY)) {
                u_int dad_failures = atomic_load_int(&DAD_FAILURES(ifp));

                if (dad_failures <= V_ip6_stableaddr_maxretries) {
                        atomic_add_int(&DAD_FAILURES(ifp), 1);
                        /* if retries exhausted, output an informative error message */
                        if (dad_failures == V_ip6_stableaddr_maxretries)
                                log(LOG_ERR, "%s: manual intervention required, consider disabling \"stableaddr\" on the interface"
                                    " or checking hostuuid for uniqueness\n",
                                    if_name(ifp));
                }
        } else {
                log(LOG_ERR, "%s: manual intervention required\n",
                    if_name(ifp));
        }

        /*
         * If the address is a link-local address formed from an interface
         * identifier based on the hardware address which is supposed to be
         * uniquely assigned (e.g., EUI-64 for an Ethernet interface), IP
         * operation on the interface SHOULD be disabled.
         * [RFC 4862, Section 5.4.5]
         */
        if (IN6_IS_ADDR_LINKLOCAL(&ia->ia_addr.sin6_addr)) {
                struct in6_addr in6;

                /*
                 * To avoid over-reaction, we only apply this logic when we are
                 * very sure that hardware addresses are supposed to be unique.
                 */
                switch (ifp->if_type) {
                case IFT_ETHER:
                case IFT_ATM:
                case IFT_IEEE1394:
                case IFT_INFINIBAND:
                        in6 = ia->ia_addr.sin6_addr;
                        if (in6_get_hw_ifid(ifp, &in6) == 0 &&
                            IN6_ARE_ADDR_EQUAL(&ia->ia_addr.sin6_addr, &in6)) {
                                ifp->if_inet6->nd_flags |= ND6_IFF_IFDISABLED;
                                log(LOG_ERR, "%s: possible hardware address "
                                    "duplication detected, disable IPv6\n",
                                    if_name(ifp));
                        }
                        break;
                }
        }
}

/*
 * Transmit a neighbour solicitation for the purpose of DAD.  Returns with the
 * DAD queue unlocked.
 */
static void
nd6_dad_ns_output(struct dadq *dp)
{
        struct in6_ifaddr *ia = (struct in6_ifaddr *)dp->dad_ifa;
        struct ifnet *ifp = dp->dad_ifa->ifa_ifp;
        int i;

        DADQ_WLOCK_ASSERT();

        dp->dad_ns_tcount++;
        if ((ifp->if_flags & IFF_UP) == 0) {
                DADQ_WUNLOCK();
                return;
        }
        if ((ifp->if_drv_flags & IFF_DRV_RUNNING) == 0) {
                DADQ_WUNLOCK();
                return;
        }

        dp->dad_ns_ocount++;
        if (V_dad_enhanced != 0) {
                for (i = 0; i < ND_OPT_NONCE_LEN32; i++)
                        dp->dad_nonce[i] = arc4random();
                /*
                 * XXXHRS: Note that in the case that
                 * DupAddrDetectTransmits > 1, multiple NS messages with
                 * different nonces can be looped back in an unexpected
                 * order.  The current implementation recognizes only
                 * the latest nonce on the sender side.  Practically it
                 * should work well in almost all cases.
                 */
        }
        DADQ_WUNLOCK();
        nd6_ns_output(ifp, NULL, NULL, &ia->ia_addr.sin6_addr,
            (uint8_t *)&dp->dad_nonce[0]);
}

static void
nd6_dad_ns_input(struct ifaddr *ifa, struct nd_opt_nonce *ndopt_nonce)
{
        struct dadq *dp;

        if (ifa == NULL)
                panic("ifa == NULL in nd6_dad_ns_input");

        /* Ignore Nonce option when Enhanced DAD is disabled. */
        if (V_dad_enhanced == 0)
                ndopt_nonce = NULL;
        DADQ_RLOCK();
        dp = nd6_dad_find(ifa, ndopt_nonce);
        if (dp != NULL)
                dp->dad_ns_icount++;
        DADQ_RUNLOCK();
}

static void
nd6_dad_na_input(struct ifaddr *ifa)
{
        struct dadq *dp;

        if (ifa == NULL)
                panic("ifa == NULL in nd6_dad_na_input");

        DADQ_RLOCK();
        dp = nd6_dad_find(ifa, NULL);
        if (dp != NULL)
                dp->dad_na_icount++;
        DADQ_RUNLOCK();
}

static void
nd6_queue_rel(void *arg)
{
        struct nd_queue *ndq = arg;
        struct ifaddr *ifa;

        ifa = ndq->ndq_ifa;
        IF_ADDR_WLOCK_ASSERT(ifa->ifa_ifp);

        /* Remove ndq from the nd_queue list and free it */
        TAILQ_REMOVE(&ifa->ifa_ifp->if_inet6->nd_queue, ndq, ndq_list);
        IF_ADDR_WUNLOCK(ifa->ifa_ifp);

        free(ndq, M_IP6NDP);
        ifa_free(ifa);
}

static void
nd6_queue_timer(void *arg)
{
        struct nd_queue *ndq = arg;
        struct ifaddr *ifa = ndq->ndq_ifa;
        struct ifnet *ifp;
        struct in6_addr daddr, taddr;
        struct sockaddr_dl sdl;
        struct epoch_tracker et;
        int delay, tlladdr;
        u_long flags;
        bool proxy;

        KASSERT(ifa != NULL, ("ND6 queue entry %p with no address", ndq));

        ifp = ifa->ifa_ifp;
        CURVNET_SET(ifp->if_vnet);
        NET_EPOCH_ENTER(et);

        daddr = ndq->ndq_daddr;
        taddr = ndq->ndq_taddr;
        tlladdr = ND6_NA_OPT_LLA;
        flags = (V_ip6_forwarding) ? ND_NA_FLAG_ROUTER : 0;
        if ((ifp->if_inet6->nd_flags & ND6_IFF_ACCEPT_RTADV) != 0 && V_ip6_norbit_raif)
                flags &= ~ND_NA_FLAG_ROUTER;

        /*
         * RFC 9131 Section 6.1.2: If the address is preferred,
         * then the Override flag SHOULD NOT be set.
         */
        if ((ndq->ndq_flags & ND6_QUEUE_FLAG_NEWGUA) != 0) {
                /*
                 * XXX: If the address is in the Optimistic state,
                 * then the Override flag MUST NOT be set.
                 * We don't support RFC 4429 yet.
                 */
                if ((ifp->if_inet6->nd_flags & ND6_IFF_PREFER_SOURCE) == 0)
                        flags |= ND_NA_FLAG_OVERRIDE;
        }
        /*
         * RFC 4861 Section 7.2.6: if link-layer address changed,
         * The Override flag MAY be set to either zero or one.
         */
        if ((ndq->ndq_flags & ND6_QUEUE_FLAG_LLADDR) != 0)
                flags |= ND_NA_FLAG_OVERRIDE;
        /* anycast advertisement delay rule (RFC 4861 7.2.7, SHOULD) */
        if ((ndq->ndq_flags & ND6_QUEUE_FLAG_ANYCAST) != 0)
                flags |= ND_NA_FLAG_SOLICITED;
        /* proxy advertisement delay rule (RFC 4861 7.2.8, SHOULD) */
        proxy = false;
        if ((ndq->ndq_flags & ND6_QUEUE_FLAG_PROXY) != 0) {
                flags |= ND_NA_FLAG_SOLICITED;
                sdl = ndq->ndq_sdl;
                proxy = true;
        }

        /*
         * if it was GRAND, wait at least a RetransTimer
         * before removing from queue.
         */
        if ((ndq->ndq_flags & ND6_QUEUE_GRAND_MASK) != 0) {
                delay = ifp->if_inet6->nd_retrans * hz / 1000;
                callout_reset(&ndq->ndq_callout, delay, nd6_queue_rel, ndq);
                IF_ADDR_WUNLOCK(ifp);
        } else
                nd6_queue_rel(ndq);

        if (__predict_true(in6_setscope(&daddr, ifp, NULL) == 0))
                nd6_na_output_fib(ifp, &daddr, &taddr, flags, tlladdr,
                    proxy ? (struct sockaddr *)&sdl : NULL, ifp->if_fib);

        NET_EPOCH_EXIT(et);
        CURVNET_RESTORE();
}

/*
 * Queue a delayed IPv6 Neighbor Advertisement.
 *
 * daddr: destination address (who the NA is sent to)
 * taddr: target address being advertised (used for proxy NAs)
 * sdl: link-layer address (used for proxy NAs)
 */
static void
nd6_queue_add(struct ifaddr *ifa, struct in6_addr *daddr,
    struct in6_addr *taddr, struct sockaddr_dl *sdl, int delay, uint32_t flags)
{
        struct nd_queue *ndq = NULL;
        struct ifnet *ifp;
        struct in6_ifextra *ext;
        char ip6buf[INET6_ADDRSTRLEN];

        NET_EPOCH_ASSERT();

        ifp = ifa->ifa_ifp;
        ext = ifp->if_inet6;
        IF_ADDR_WLOCK(ifp);
        /*
         * if request comes from GRAND, check whether another delayed
         * GRAND NA exists in the queue.
         * If it exists, cancel previous one and reuse its ndq.
         */
        if ((flags & ND6_QUEUE_GRAND_MASK) != 0) {
                TAILQ_FOREACH(ndq, &ext->nd_queue, ndq_list) {
                        if (ndq->ndq_ifa == ifa &&
                            (flags & ND6_QUEUE_GRAND_MASK) != 0)
                                break;
                }
        }
        if (ndq == NULL) {
                ndq = malloc(sizeof(*ndq), M_IP6NDP, M_NOWAIT | M_ZERO);
                if (ndq == NULL) {
                        log(LOG_ERR, "%s: memory allocation failed for %s(%s)\n",
                            __func__, ip6_sprintf(ip6buf, IFA_IN6(ifa)),
                            ifp ? if_name(ifp) : "???");
                        IF_ADDR_WUNLOCK(ifp);
                        return;
                }

                callout_init_mtx(&ndq->ndq_callout, &ifp->if_addr_lock,
                    CALLOUT_TRYLOCK | CALLOUT_RETURNUNLOCKED);
                ifa_ref(ifa);
                ndq->ndq_ifa = ifa;
                TAILQ_INSERT_TAIL(&ext->nd_queue, ndq, ndq_list);
        }

        memcpy(&ndq->ndq_daddr, daddr, sizeof(struct in6_addr));
        /*
         * For proxy NAs, the target address (taddr) being advertised differs from
         * the interface address (ifa), so we must explicitly store both the proxy
         * target address and its link-layer address (sdl).
         * For non-proxy NAs, use the interface address (ifa) itself as the target.
         */
        if ((flags & ND6_QUEUE_FLAG_PROXY) != 0) {
                memcpy(&ndq->ndq_taddr, taddr, sizeof(struct in6_addr));
                memcpy(&ndq->ndq_sdl, sdl, sizeof(struct sockaddr_dl));
        } else
                memcpy(&ndq->ndq_taddr, IFA_IN6(ifa), sizeof(struct in6_addr));
        ndq->ndq_flags = flags;

        nd6log((LOG_DEBUG, "%s: delay IPv6 NA for %s\n", if_name(ifp),
            ip6_sprintf(ip6buf, IFA_IN6(ifa))));
        callout_reset(&ndq->ndq_callout, delay, nd6_queue_timer, ndq);
        IF_ADDR_WUNLOCK(ifp);
}

/*
 * Start Gratuitous Neighbor Discovery (GRAND) for specified address.
 * Called after DAD completes and by interface link layer change event.
 */
void
nd6_grand_start(struct ifaddr *ifa, uint32_t flags)
{
        struct nd_queue *ndq;
        struct in6_ifextra *ext = ifa->ifa_ifp->if_inet6;
        struct in6_addr daddr = IN6ADDR_ANY_INIT;
        int delay, count = 0;

        NET_EPOCH_ASSERT();
        /* If we don't need GRAND, don't do it. */
        if (V_ip6_grand_count == 0 ||
            ifa->ifa_carp != NULL)
                return;

        /* Check if new address is global */
        if ((flags & ND6_QUEUE_FLAG_NEWGUA) != 0 &&
            in6_addrscope(IFA_IN6(ifa)) != IPV6_ADDR_SCOPE_GLOBAL)
                return;

        /*
         * RFC 9131 Section 6.1.2: These advertisements MUST be
         * separated by at least RetransTimer seconds.
         */
        TAILQ_FOREACH(ndq, &ext->nd_queue, ndq_list) {
                /*
                 * RFC 9131 Section 6.1.2: a node SHOULD send
                 * up to MAX_NEIGHBOR_ADVERTISEMENT Neighbor Advertisement messages.
                 * Make sure we don't queue GRAND more than V_ip6_grand_count
                 * per interface.
                 * Since this limitation only applies to GRAND, don't
                 * count non-GRAND ndq.
                 */
                if ((ndq->ndq_flags & ND6_QUEUE_GRAND_MASK) == 0)
                        continue;

                count++;
                if (count >= V_ip6_grand_count)
                        return;
        }

        /*
         * RFC 9131 Section 6.1.2: if new global address added,
         * use the all-routers multicast address.
         */
        if ((flags & ND6_QUEUE_FLAG_NEWGUA) != 0)
                daddr = in6addr_linklocal_allrouters;

        /*
         * RFC 4861 Section 7.2.6: if link-layer address changed,
         * use the all-nodes multicast address.
         */
        if ((flags & ND6_QUEUE_FLAG_LLADDR) != 0)
                daddr = in6addr_linklocal_allnodes;

        delay = ext->nd_retrans * hz / 1000;
        nd6_queue_add(ifa, &daddr, NULL, NULL, count * delay, flags);
}

/*
 * drain nd6 queue. used for address removals.
 */
void
nd6_queue_stop(struct ifaddr *ifa)
{
        struct nd_queue *ndq, *dndq;
        struct ifnet *ifp;

        ifp = ifa->ifa_ifp;
        IF_ADDR_WLOCK(ifp);
        TAILQ_FOREACH_SAFE(ndq, &ifp->if_inet6->nd_queue, ndq_list, dndq) {
                if (ndq->ndq_ifa != ifa)
                        continue;

                callout_stop(&ndq->ndq_callout);

                /* Remove ndq from the nd_queue list and free it */
                TAILQ_REMOVE(&ifa->ifa_ifp->if_inet6->nd_queue, ndq, ndq_list);
                free(ndq, M_IP6NDP);
                ifa_free(ifa);
        }
        IF_ADDR_WUNLOCK(ifp);
}