ZeroTierOne/osdep/MacKextEthernetTap.cpp

/*
 * Copyright (c)2019 ZeroTier, Inc.
 *
 * Use of this software is governed by the Business Source License included
 * in the LICENSE.TXT file in the project's root directory.
 *
 * Change Date: 2026-01-01
 *
 * On the date above, in accordance with the Business Source License, use
 * of this software will be governed by version 2.0 of the Apache License.
 */
/****/

#include "MacDNSHelper.hpp"

#include <arpa/inet.h>
#include <errno.h>
#include <fcntl.h>
#include <net/if.h>
#include <net/if_arp.h>
#include <net/if_dl.h>
#include <net/if_media.h>
#include <net/route.h>
#include <netinet/icmp6.h>
#include <netinet/in.h>
#include <netinet/in_var.h>
#include <netinet6/in6_var.h>
#include <signal.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/cdefs.h>
#include <sys/ioctl.h>
#include <sys/param.h>
#include <sys/select.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/sysctl.h>
#include <sys/types.h>
#include <sys/uio.h>
#include <sys/wait.h>
#include <unistd.h>

// OSX compile fix... in6_var defines this in a struct which namespaces it for C++ ... why?!?
struct prf_ra {
    u_char onlink : 1;
    u_char autonomous : 1;
    u_char reserved : 6;
} prf_ra;

#include <ifaddrs.h>
#include <netinet6/nd6.h>

// These are KERNEL_PRIVATE... why?
#ifndef SIOCAUTOCONF_START
#define SIOCAUTOCONF_START _IOWR('i', 132, struct in6_ifreq) /* accept rtadvd on this interface */
#endif
#ifndef SIOCAUTOCONF_STOP
#define SIOCAUTOCONF_STOP _IOWR('i', 133, struct in6_ifreq) /* stop accepting rtadv for this interface */
#endif

// --------------------------------------------------------------------------
// --------------------------------------------------------------------------
// This source is from:
// http://www.opensource.apple.com/source/Libinfo/Libinfo-406.17/gen.subproj/getifmaddrs.c?txt
// It's here because OSX 10.6 does not have this convenience function.

#define SALIGN         (sizeof(uint32_t) - 1)
#define SA_RLEN(sa)    ((sa)->sa_len ? (((sa)->sa_len + SALIGN) & ~SALIGN) : (SALIGN + 1))
#define MAX_SYSCTL_TRY 5
#define RTA_MASKS      (RTA_GATEWAY | RTA_IFP | RTA_IFA)

/* FreeBSD uses NET_RT_IFMALIST and RTM_NEWMADDR from <sys/socket.h> */
/* We can use NET_RT_IFLIST2 and RTM_NEWMADDR2 on Darwin */
// #define DARWIN_COMPAT

// #ifdef DARWIN_COMPAT
#define GIM_SYSCTL_MIB NET_RT_IFLIST2
#define GIM_RTM_ADDR   RTM_NEWMADDR2
// #else
// #define GIM_SYSCTL_MIB NET_RT_IFMALIST
// #define GIM_RTM_ADDR RTM_NEWMADDR
// #endif

// Not in 10.6 includes so use our own
struct _intl_ifmaddrs {
    struct _intl_ifmaddrs* ifma_next;
    struct sockaddr* ifma_name;
    struct sockaddr* ifma_addr;
    struct sockaddr* ifma_lladdr;
};

static inline int _intl_getifmaddrs(struct _intl_ifmaddrs** pif)
{
    int icnt = 1;
    int dcnt = 0;
    int ntry = 0;
    size_t len;
    size_t needed;
    int mib[6];
    int i;
    char* buf;
    char* data;
    char* next;
    char* p;
    struct ifma_msghdr2* ifmam;
    struct _intl_ifmaddrs *ifa, *ift;
    struct rt_msghdr* rtm;
    struct sockaddr* sa;

    mib[0] = CTL_NET;
    mib[1] = PF_ROUTE;
    mib[2] = 0; /* protocol */
    mib[3] = 0; /* wildcard address family */
    mib[4] = GIM_SYSCTL_MIB;
    mib[5] = 0; /* no flags */
    do {
        if (sysctl(mib, 6, NULL, &needed, NULL, 0) < 0)
            return (-1);
        if ((buf = (char*)malloc(needed)) == NULL)
            return (-1);
        if (sysctl(mib, 6, buf, &needed, NULL, 0) < 0) {
            if (errno != ENOMEM || ++ntry >= MAX_SYSCTL_TRY) {
                free(buf);
                return (-1);
            }
            free(buf);
            buf = NULL;
        }
    } while (buf == NULL);

    for (next = buf; next < buf + needed; next += rtm->rtm_msglen) {
        rtm = (struct rt_msghdr*)(void*)next;
        if (rtm->rtm_version != RTM_VERSION)
            continue;
        switch (rtm->rtm_type) {
            case GIM_RTM_ADDR:
                ifmam = (struct ifma_msghdr2*)(void*)rtm;
                if ((ifmam->ifmam_addrs & RTA_IFA) == 0)
                    break;
                icnt++;
                p = (char*)(ifmam + 1);
                for (i = 0; i < RTAX_MAX; i++) {
                    if ((RTA_MASKS & ifmam->ifmam_addrs & (1 << i)) == 0)
                        continue;
                    sa = (struct sockaddr*)(void*)p;
                    len = SA_RLEN(sa);
                    dcnt += len;
                    p += len;
                }
                break;
        }
    }

    data = (char*)malloc(sizeof(struct _intl_ifmaddrs) * icnt + dcnt);
    if (data == NULL) {
        free(buf);
        return (-1);
    }

    ifa = (struct _intl_ifmaddrs*)(void*)data;
    data += sizeof(struct _intl_ifmaddrs) * icnt;

    memset(ifa, 0, sizeof(struct _intl_ifmaddrs) * icnt);
    ift = ifa;

    for (next = buf; next < buf + needed; next += rtm->rtm_msglen) {
        rtm = (struct rt_msghdr*)(void*)next;
        if (rtm->rtm_version != RTM_VERSION)
            continue;

        switch (rtm->rtm_type) {
            case GIM_RTM_ADDR:
                ifmam = (struct ifma_msghdr2*)(void*)rtm;
                if ((ifmam->ifmam_addrs & RTA_IFA) == 0)
                    break;

                p = (char*)(ifmam + 1);
                for (i = 0; i < RTAX_MAX; i++) {
                    if ((RTA_MASKS & ifmam->ifmam_addrs & (1 << i)) == 0)
                        continue;
                    sa = (struct sockaddr*)(void*)p;
                    len = SA_RLEN(sa);
                    switch (i) {
                        case RTAX_GATEWAY:
                            ift->ifma_lladdr = (struct sockaddr*)(void*)data;
                            memcpy(data, p, len);
                            data += len;
                            break;

                        case RTAX_IFP:
                            ift->ifma_name = (struct sockaddr*)(void*)data;
                            memcpy(data, p, len);
                            data += len;
                            break;

                        case RTAX_IFA:
                            ift->ifma_addr = (struct sockaddr*)(void*)data;
                            memcpy(data, p, len);
                            data += len;
                            break;

                        default:
                            data += len;
                            break;
                    }
                    p += len;
                }
                ift->ifma_next = ift + 1;
                ift = ift->ifma_next;
                break;
        }
    }

    free(buf);

    if (ift > ifa) {
        ift--;
        ift->ifma_next = NULL;
        *pif = ifa;
    }
    else {
        *pif = NULL;
        free(ifa);
    }
    return (0);
}

static inline void _intl_freeifmaddrs(struct _intl_ifmaddrs* ifmp)
{
    free(ifmp);
}

// --------------------------------------------------------------------------
// --------------------------------------------------------------------------

#include "../node/Constants.hpp"
#include "../node/Dictionary.hpp"
#include "../node/Mutex.hpp"
#include "../node/Utils.hpp"
#include "MacKextEthernetTap.hpp"
#include "OSUtils.hpp"

#include <algorithm>
#include <map>
#include <set>
#include <string>

// ff:ff:ff:ff:ff:ff with no ADI
static const ZeroTier::MulticastGroup _blindWildcardMulticastGroup(ZeroTier::MAC(0xff), 0);

static inline bool _setIpv6Stuff(const char* ifname, bool performNUD, bool acceptRouterAdverts)
{
    struct in6_ndireq nd;
    struct in6_ifreq ifr;

    int s = socket(AF_INET6, SOCK_DGRAM, 0);
    if (s <= 0)
        return false;

    memset(&nd, 0, sizeof(nd));
    strncpy(nd.ifname, ifname, sizeof(nd.ifname));

    if (ioctl(s, SIOCGIFINFO_IN6, &nd)) {
        close(s);
        return false;
    }

    unsigned long oldFlags = (unsigned long)nd.ndi.flags;

    if (performNUD)
        nd.ndi.flags |= ND6_IFF_PERFORMNUD;
    else
        nd.ndi.flags &= ~ND6_IFF_PERFORMNUD;

    if (oldFlags != (unsigned long)nd.ndi.flags) {
        if (ioctl(s, SIOCSIFINFO_FLAGS, &nd)) {
            close(s);
            return false;
        }
    }

    memset(&ifr, 0, sizeof(ifr));
    strncpy(ifr.ifr_name, ifname, sizeof(ifr.ifr_name));
    if (ioctl(s, acceptRouterAdverts ? SIOCAUTOCONF_START : SIOCAUTOCONF_STOP, &ifr)) {
        close(s);
        return false;
    }

    close(s);
    return true;
}

namespace ZeroTier {

static long globalTapsRunning = 0;
static Mutex globalTapCreateLock;

MacKextEthernetTap::MacKextEthernetTap(
    const char* homePath,
    const MAC& mac,
    unsigned int mtu,
    unsigned int metric,
    uint64_t nwid,
    const char* friendlyName,
    void (*handler)(void*, void*, uint64_t, const MAC&, const MAC&, unsigned int, unsigned int, const void* data, unsigned int len),
    void* arg)
    : _handler(handler)
    , _arg(arg)
    , _nwid(nwid)
    , _homePath(homePath)
    , _mtu(mtu)
    , _metric(metric)
    , _fd(0)
    , _enabled(true)
{
    char devpath[64], ethaddr[64], mtustr[32], metstr[32], nwids[32];
    struct stat stattmp;

    OSUtils::ztsnprintf(nwids, sizeof(nwids), "%.16llx", nwid);

    Mutex::Lock _gl(globalTapCreateLock);

    if (::stat("/dev/zt0", &stattmp)) {
        long kextpid = (long)fork();
        if (kextpid == 0) {
            ::chdir(homePath);
            OSUtils::redirectUnixOutputs("/dev/null", (const char*)0);
            ::execl("/sbin/kextload", "/sbin/kextload", "-q", "-repository", homePath, "tap.kext", (const char*)0);
            ::_exit(-1);
        }
        else if (kextpid > 0) {
            int exitcode = -1;
            ::waitpid(kextpid, &exitcode, 0);
        }
        ::usleep(500);   // give tap device driver time to start up and try again
        if (::stat("/dev/zt0", &stattmp))
            throw std::runtime_error("/dev/zt# tap devices do not exist and cannot load tap.kext");
    }

    // Try to reopen the last device we had, if we had one and it's still unused.
    std::map<std::string, std::string> globalDeviceMap;
    FILE* devmapf = fopen((_homePath + ZT_PATH_SEPARATOR_S + "devicemap").c_str(), "r");
    if (devmapf) {
        char buf[256];
        while (fgets(buf, sizeof(buf), devmapf)) {
            char* x = (char*)0;
            char* y = (char*)0;
            char* saveptr = (char*)0;
            for (char* f = Utils::stok(buf, "\r\n=", &saveptr); (f); f = Utils::stok((char*)0, "\r\n=", &saveptr)) {
                if (! x)
                    x = f;
                else if (! y)
                    y = f;
                else
                    break;
            }
            if ((x) && (y) && (x[0]) && (y[0]))
                globalDeviceMap[x] = y;
        }
        fclose(devmapf);
    }
    bool recalledDevice = false;
    std::map<std::string, std::string>::const_iterator gdmEntry = globalDeviceMap.find(nwids);
    if (gdmEntry != globalDeviceMap.end()) {
        std::string devpath("/dev/");
        devpath.append(gdmEntry->second);
        if (stat(devpath.c_str(), &stattmp) == 0) {
            _fd = ::open(devpath.c_str(), O_RDWR);
            if (_fd > 0) {
                _dev = gdmEntry->second;
                recalledDevice = true;
            }
        }
    }

    // Open the first unused tap device if we didn't recall a previous one.
    if (! recalledDevice) {
        for (int i = 0; i < 64; ++i) {
            OSUtils::ztsnprintf(devpath, sizeof(devpath), "/dev/zt%d", i);
            if (stat(devpath, &stattmp))
                throw std::runtime_error("no more TAP devices available");
            _fd = ::open(devpath, O_RDWR);
            if (_fd > 0) {
                char foo[16];
                OSUtils::ztsnprintf(foo, sizeof(foo), "zt%d", i);
                _dev = foo;
                break;
            }
        }
    }

    if (_fd <= 0)
        throw std::runtime_error("unable to open TAP device or no more devices available");

    if (fcntl(_fd, F_SETFL, fcntl(_fd, F_GETFL) & ~O_NONBLOCK) == -1) {
        ::close(_fd);
        throw std::runtime_error("unable to set flags on file descriptor for TAP device");
    }

    // Configure MAC address and MTU, bring interface up
    OSUtils::ztsnprintf(ethaddr, sizeof(ethaddr), "%.2x:%.2x:%.2x:%.2x:%.2x:%.2x", (int)mac[0], (int)mac[1], (int)mac[2], (int)mac[3], (int)mac[4], (int)mac[5]);
    OSUtils::ztsnprintf(mtustr, sizeof(mtustr), "%u", _mtu);
    OSUtils::ztsnprintf(metstr, sizeof(metstr), "%u", _metric);
    long cpid = (long)fork();
    if (cpid == 0) {
        ::execl("/sbin/ifconfig", "/sbin/ifconfig", _dev.c_str(), "lladdr", ethaddr, "mtu", mtustr, "metric", metstr, "up", (const char*)0);
        ::_exit(-1);
    }
    else if (cpid > 0) {
        int exitcode = -1;
        ::waitpid(cpid, &exitcode, 0);
        if (exitcode) {
            ::close(_fd);
            throw std::runtime_error("ifconfig failure setting link-layer address and activating tap interface");
        }
    }

    _setIpv6Stuff(_dev.c_str(), true, false);

    // Set close-on-exec so that devices cannot persist if we fork/exec for update
    fcntl(_fd, F_SETFD, fcntl(_fd, F_GETFD) | FD_CLOEXEC);

    ::pipe(_shutdownSignalPipe);

    ++globalTapsRunning;

    globalDeviceMap[nwids] = _dev;
    devmapf = fopen((_homePath + ZT_PATH_SEPARATOR_S + "devicemap").c_str(), "w");
    if (devmapf) {
        gdmEntry = globalDeviceMap.begin();
        while (gdmEntry != globalDeviceMap.end()) {
            fprintf(devmapf, "%s=%s\n", gdmEntry->first.c_str(), gdmEntry->second.c_str());
            ++gdmEntry;
        }
        fclose(devmapf);
    }

    _thread = Thread::start(this);
}

MacKextEthernetTap::~MacKextEthernetTap()
{
    MacDNSHelper::removeDNS(_nwid);

    ::write(_shutdownSignalPipe[1], "\0", 1);   // causes thread to exit
    Thread::join(_thread);
    for (std::thread& t : _rxThreads) {
        t.join();
    }
    ::close(_fd);
    ::close(_shutdownSignalPipe[0]);
    ::close(_shutdownSignalPipe[1]);

    {
        Mutex::Lock _gl(globalTapCreateLock);
        if (--globalTapsRunning <= 0) {
            globalTapsRunning = 0;   // sanity check -- should not be possible

            char tmp[16384];
            sprintf(tmp, "%s/%s", _homePath.c_str(), "tap.kext");
            long kextpid = (long)fork();
            if (kextpid == 0) {
                OSUtils::redirectUnixOutputs("/dev/null", (const char*)0);
                ::execl("/sbin/kextunload", "/sbin/kextunload", tmp, (const char*)0);
                ::_exit(-1);
            }
            else if (kextpid > 0) {
                int exitcode = -1;
                ::waitpid(kextpid, &exitcode, 0);
            }
        }
    }
}

void MacKextEthernetTap::setEnabled(bool en)
{
    _enabled = en;
    // TODO: interface status change
}

bool MacKextEthernetTap::enabled() const
{
    return _enabled;
}

bool MacKextEthernetTap::addIp(const InetAddress& ip)
{
    if (! ip)
        return false;

    long cpid = (long)fork();
    if (cpid == 0) {
        char tmp[128];
        ::execl("/sbin/ifconfig", "/sbin/ifconfig", _dev.c_str(), (ip.ss_family == AF_INET6) ? "inet6" : "inet", ip.toString(tmp), "alias", (const char*)0);
        ::_exit(-1);
    }
    else if (cpid > 0) {
        int exitcode = -1;
        ::waitpid(cpid, &exitcode, 0);
        return (exitcode == 0);
    }   // else return false...

    return false;
}

bool MacKextEthernetTap::removeIp(const InetAddress& ip)
{
    if (! ip)
        return true;
    std::vector<InetAddress> allIps(ips());
    for (std::vector<InetAddress>::iterator i(allIps.begin()); i != allIps.end(); ++i) {
        if (*i == ip) {
            long cpid = (long)fork();
            if (cpid == 0) {
                char tmp[128];
                execl("/sbin/ifconfig", "/sbin/ifconfig", _dev.c_str(), (ip.ss_family == AF_INET6) ? "inet6" : "inet", ip.toIpString(tmp), "-alias", (const char*)0);
                _exit(-1);
            }
            else if (cpid > 0) {
                int exitcode = -1;
                waitpid(cpid, &exitcode, 0);
                return (exitcode == 0);
            }
        }
    }
    return false;
}

std::vector<InetAddress> MacKextEthernetTap::ips() const
{
    struct ifaddrs* ifa = (struct ifaddrs*)0;
    if (getifaddrs(&ifa))
        return std::vector<InetAddress>();

    std::vector<InetAddress> r;

    struct ifaddrs* p = ifa;
    while (p) {
        if ((! strcmp(p->ifa_name, _dev.c_str())) && (p->ifa_addr) && (p->ifa_netmask) && (p->ifa_addr->sa_family == p->ifa_netmask->sa_family)) {
            switch (p->ifa_addr->sa_family) {
                case AF_INET: {
                    struct sockaddr_in* sin = (struct sockaddr_in*)p->ifa_addr;
                    struct sockaddr_in* nm = (struct sockaddr_in*)p->ifa_netmask;
                    r.push_back(InetAddress(&(sin->sin_addr.s_addr), 4, Utils::countBits((uint32_t)nm->sin_addr.s_addr)));
                } break;
                case AF_INET6: {
                    struct sockaddr_in6* sin = (struct sockaddr_in6*)p->ifa_addr;
                    struct sockaddr_in6* nm = (struct sockaddr_in6*)p->ifa_netmask;
                    uint32_t b[4];
                    memcpy(b, nm->sin6_addr.s6_addr, sizeof(b));
                    r.push_back(InetAddress(sin->sin6_addr.s6_addr, 16, Utils::countBits(b[0]) + Utils::countBits(b[1]) + Utils::countBits(b[2]) + Utils::countBits(b[3])));
                } break;
            }
        }
        p = p->ifa_next;
    }

    if (ifa)
        freeifaddrs(ifa);

    std::sort(r.begin(), r.end());
    r.erase(std::unique(r.begin(), r.end()), r.end());

    return r;
}

void MacKextEthernetTap::put(const MAC& from, const MAC& to, unsigned int etherType, const void* data, unsigned int len)
{
    char putBuf[ZT_MAX_MTU + 64];
    if ((_fd > 0) && (len <= _mtu) && (_enabled)) {
        to.copyTo(putBuf, 6);
        from.copyTo(putBuf + 6, 6);
        *((uint16_t*)(putBuf + 12)) = htons((uint16_t)etherType);
        memcpy(putBuf + 14, data, len);
        len += 14;
        ::write(_fd, putBuf, len);
    }
}

std::string MacKextEthernetTap::deviceName() const
{
    return _dev;
}

void MacKextEthernetTap::setFriendlyName(const char* friendlyName)
{
}

void MacKextEthernetTap::scanMulticastGroups(std::vector<MulticastGroup>& added, std::vector<MulticastGroup>& removed)
{
    std::vector<MulticastGroup> newGroups;

    struct _intl_ifmaddrs* ifmap = (struct _intl_ifmaddrs*)0;
    if (! _intl_getifmaddrs(&ifmap)) {
        struct _intl_ifmaddrs* p = ifmap;
        while (p) {
            if (p->ifma_addr->sa_family == AF_LINK) {
                struct sockaddr_dl* in = (struct sockaddr_dl*)p->ifma_name;
                struct sockaddr_dl* la = (struct sockaddr_dl*)p->ifma_addr;
                if ((la->sdl_alen == 6) && (in->sdl_nlen <= _dev.length()) && (! memcmp(_dev.data(), in->sdl_data, in->sdl_nlen)))
                    newGroups.push_back(MulticastGroup(MAC(la->sdl_data + la->sdl_nlen, 6), 0));
            }
            p = p->ifma_next;
        }
        _intl_freeifmaddrs(ifmap);
    }

    std::vector<InetAddress> allIps(ips());
    for (std::vector<InetAddress>::iterator ip(allIps.begin()); ip != allIps.end(); ++ip)
        newGroups.push_back(MulticastGroup::deriveMulticastGroupForAddressResolution(*ip));

    std::sort(newGroups.begin(), newGroups.end());
    std::unique(newGroups.begin(), newGroups.end());

    for (std::vector<MulticastGroup>::iterator m(newGroups.begin()); m != newGroups.end(); ++m) {
        if (! std::binary_search(_multicastGroups.begin(), _multicastGroups.end(), *m))
            added.push_back(*m);
    }
    for (std::vector<MulticastGroup>::iterator m(_multicastGroups.begin()); m != _multicastGroups.end(); ++m) {
        if (! std::binary_search(newGroups.begin(), newGroups.end(), *m))
            removed.push_back(*m);
    }

    _multicastGroups.swap(newGroups);
}

void MacKextEthernetTap::setMtu(unsigned int mtu)
{
    if (mtu != _mtu) {
        _mtu = mtu;
        long cpid = (long)fork();
        if (cpid == 0) {
            char tmp[64];
            OSUtils::ztsnprintf(tmp, sizeof(tmp), "%u", mtu);
            execl("/sbin/ifconfig", "/sbin/ifconfig", _dev.c_str(), "mtu", tmp, (const char*)0);
            _exit(-1);
        }
        else if (cpid > 0) {
            int exitcode = -1;
            waitpid(cpid, &exitcode, 0);
        }
    }
}

void MacKextEthernetTap::threadMain() throw()
{
    fd_set readfds, nullfds;
    MAC to, from;
    int n, nfds, r;
    char getBuf[ZT_MAX_MTU + 64];

    Thread::sleep(500);

    FD_ZERO(&readfds);
    FD_ZERO(&nullfds);
    nfds = (int)std::max(_shutdownSignalPipe[0], _fd) + 1;

    r = 0;
    for (;;) {
        FD_SET(_shutdownSignalPipe[0], &readfds);
        FD_SET(_fd, &readfds);
        select(nfds, &readfds, &nullfds, &nullfds, (struct timeval*)0);

        if (FD_ISSET(_shutdownSignalPipe[0], &readfds))   // writes to shutdown pipe terminate thread
            break;

        if (FD_ISSET(_fd, &readfds)) {
            n = (int)::read(_fd, getBuf + r, sizeof(getBuf) - r);
            if (n < 0) {
                if ((errno != EINTR) && (errno != ETIMEDOUT))
                    break;
            }
            else {
                // Some tap drivers like to send the ethernet frame and the
                // payload in two chunks, so handle that by accumulating
                // data until we have at least a frame.
                r += n;
                if (r > 14) {
                    if (r > ((int)_mtu + 14))   // sanity check for weird TAP behavior on some platforms
                        r = _mtu + 14;

                    if (_enabled) {
                        to.setTo(getBuf, 6);
                        from.setTo(getBuf + 6, 6);
                        unsigned int etherType = ntohs(((const uint16_t*)getBuf)[6]);
                        // TODO: VLAN support
                        _handler(_arg, (void*)0, _nwid, from, to, etherType, 0, (const void*)(getBuf + 14), r - 14);
                    }

                    r = 0;
                }
            }
        }
    }
}

void MacKextEthernetTap::setDns(const char* domain, const std::vector<InetAddress>& servers)
{
    MacDNSHelper::setDNS(_nwid, domain, servers);
}

}   // namespace ZeroTier