diff --git a/attic/OSXEthernetTap.cpp.utun-work-in-progress b/attic/OSXEthernetTap.cpp.utun-work-in-progress
new file mode 100644
index 000000000..b7a05334d
--- /dev/null
+++ b/attic/OSXEthernetTap.cpp.utun-work-in-progress
@@ -0,0 +1,832 @@
+/*
+ * ZeroTier One - Network Virtualization Everywhere
+ * Copyright (C) 2011-2015  ZeroTier, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * --
+ *
+ * ZeroTier may be used and distributed under the terms of the GPLv3, which
+ * are available at: http://www.gnu.org/licenses/gpl-3.0.html
+ *
+ * If you would like to embed ZeroTier into a commercial application or
+ * redistribute it in a modified binary form, please contact ZeroTier Networks
+ * LLC. Start here: http://www.zerotier.com/
+ */
+
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <errno.h>
+
+#include <unistd.h>
+#include <signal.h>
+
+#include <fcntl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/ioctl.h>
+#include <sys/wait.h>
+#include <sys/select.h>
+#include <sys/cdefs.h>
+#include <sys/uio.h>
+#include <sys/param.h>
+#include <sys/sysctl.h>
+#include <sys/ioctl.h>
+#include <sys/socket.h>
+#include <sys/sys_domain.h>
+#include <sys/kern_control.h>
+#include <net/if_utun.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <net/route.h>
+#include <net/if.h>
+#include <net/if_arp.h>
+#include <net/if_dl.h>
+#include <net/if_media.h>
+#include <netinet6/in6_var.h>
+#include <netinet/in_var.h>
+#include <netinet/icmp6.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 <netinet6/nd6.h>
+#include <ifaddrs.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 <string>
+#include <map>
+#include <set>
+#include <algorithm>
+
+#include "../node/Constants.hpp"
+#include "../node/Utils.hpp"
+#include "../node/Mutex.hpp"
+#include "../node/Dictionary.hpp"
+#include "Arp.hpp"
+#include "OSUtils.hpp"
+#include "OSXEthernetTap.hpp"
+
+// 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;
+}
+
+// Create an OSX-native utun device (utun# where # is desiredNumber)
+// Adapted from public domain utun example code by Jonathan Levin
+static int _make_utun(int desiredNumber)
+{
+	struct sockaddr_ctl sc;
+	struct ctl_info ctlInfo;
+	struct ifreq ifr;
+
+	memset(&ctlInfo, 0, sizeof(ctlInfo));
+	if (strlcpy(ctlInfo.ctl_name, UTUN_CONTROL_NAME, sizeof(ctlInfo.ctl_name)) >= sizeof(ctlInfo.ctl_name)) {
+		return -1;
+	}
+
+	int fd = socket(PF_SYSTEM, SOCK_DGRAM, SYSPROTO_CONTROL);
+	if (fd == -1)
+		return -1;
+	if (ioctl(fd, CTLIOCGINFO, &ctlInfo) == -1) {
+		close(fd);
+		return -1;
+	}
+
+	sc.sc_id = ctlInfo.ctl_id;
+	sc.sc_len = sizeof(sc);
+	sc.sc_family = AF_SYSTEM;
+	sc.ss_sysaddr = AF_SYS_CONTROL;
+	sc.sc_unit = desiredNumber + 1;
+
+	if (connect(fd, (struct sockaddr *)&sc, sizeof(sc)) == -1) {
+		close(fd);
+		return -1;
+	}
+
+	memset(&ifr,0,sizeof(ifr));
+	sprintf(ifr.ifr_name,"utun%d",desiredNumber);
+	if (ioctl(fd,SIOCGIFFLAGS,(void *)&ifr) < 0) {
+		printf("SIOCGIFFLAGS failed\n");
+	}
+	ifr.ifr_flags &= ~IFF_POINTOPOINT;
+	if (ioctl(fd,SIOCSIFFLAGS,(void *)&ifr) < 0) {
+		printf("clear IFF_POINTOPOINT failed\n");
+	}
+
+	return fd;
+}
+
+namespace ZeroTier {
+
+static long globalTapsRunning = 0;
+static Mutex globalTapCreateLock;
+
+OSXEthernetTap::OSXEthernetTap(
+	const char *homePath,
+	const MAC &mac,
+	unsigned int mtu,
+	unsigned int metric,
+	uint64_t nwid,
+	const char *friendlyName,
+	void (*handler)(void *,uint64_t,const MAC &,const MAC &,unsigned int,unsigned int,const void *data,unsigned int len),
+	void *arg) :
+	_handler(handler),
+	_arg(arg),
+	_arp((Arp *)0),
+	_nwid(nwid),
+	_homePath(homePath),
+	_mtu(mtu),
+	_metric(metric),
+	_fd(0),
+	_utun(false),
+	_enabled(true)
+{
+	char devpath[64],ethaddr[64],mtustr[32],metstr[32],nwids[32];
+	struct stat stattmp;
+
+	Utils::snprintf(nwids,sizeof(nwids),"%.16llx",nwid);
+
+	if (mtu > 2800)
+		throw std::runtime_error("max tap MTU is 2800");
+
+	Mutex::Lock _gl(globalTapCreateLock);
+
+	// Read remembered previous device name, if any -- we'll try to reuse
+	Dictionary devmap;
+	std::string desiredDevice;
+	{
+		std::string devmapbuf;
+		if (OSUtils::readFile((_homePath + ZT_PATH_SEPARATOR_S + "devicemap").c_str(),devmapbuf)) {
+			devmap.fromString(devmapbuf);
+			desiredDevice = devmap.get(nwids,"");
+		}
+	}
+
+	if (::stat((_homePath + ZT_PATH_SEPARATOR_S + "tap.kext").c_str(),&stattmp) == 0) {
+		// Try to init kext if it's there, otherwise revert to utun mode
+
+		if (::stat("/dev/zt0",&stattmp)) {
+			long kextpid = (long)vfork();
+			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))
+				_utun = true;
+		}
+
+		if (!_utun) {
+			// See if we can re-use the last device we had.
+			bool recalledDevice = false;
+			if (desiredDevice.length() > 2) {
+				Utils::snprintf(devpath,sizeof(devpath),"/dev/%s",desiredDevice.c_str());
+				if (stat(devpath,&stattmp) == 0) {
+					_fd = ::open(devpath,O_RDWR);
+					if (_fd > 0) {
+						_dev = desiredDevice;
+						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) {
+					Utils::snprintf(devpath,sizeof(devpath),"/dev/zt%d",i);
+					if (stat(devpath,&stattmp)) {
+						_utun = true;
+						break;
+					}
+					_fd = ::open(devpath,O_RDWR);
+					if (_fd > 0) {
+						char foo[16];
+						Utils::snprintf(foo,sizeof(foo),"zt%d",i);
+						_dev = foo;
+						break;
+					}
+				}
+			}
+			if (_fd <= 0)
+				_utun = true;
+		}
+	} else {
+		_utun = true;
+	}
+
+	if (_utun) {
+		// Use OSX built-in utun device if kext is not available or doesn't work
+
+		int utunNo = 0;
+
+		if ((desiredDevice.length() > 4)&&(desiredDevice.substr(0,4) == "utun")) {
+			utunNo = Utils::strToInt(desiredDevice.substr(4).c_str());
+			if (utunNo >= 0)
+				_fd = _make_utun(utunNo);
+		}
+
+		if (_fd <= 0) {
+			// Start at utun8 to leave lower utuns unused since other stuff might
+			// want them -- OpenVPN, cjdns, etc. I'm not sure if those are smart
+			// enough to scan upward like this.
+			for(utunNo=8;utunNo<=256;++utunNo) {
+				if ((_fd = _make_utun(utunNo)) > 0)
+					break;
+			}
+		}
+
+		if (_fd <= 0)
+			throw std::runtime_error("unable to find/load ZeroTier tap driver OR use built-in utun driver in OSX; permission or system problem or too many open devices?");
+
+		Utils::snprintf(devpath,sizeof(devpath),"utun%d",utunNo);
+		_dev = devpath;
+
+		// Configure address and bring it up
+		Utils::snprintf(mtustr,sizeof(mtustr),"%u",_mtu);
+		Utils::snprintf(metstr,sizeof(metstr),"%u",_metric);
+		long cpid = (long)vfork();
+		if (cpid == 0) {
+			::execl("/sbin/ifconfig","/sbin/ifconfig",_dev.c_str(),"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 activating utun interface");
+			}
+		}
+
+	} else {
+		// Use our ZeroTier OSX tun/tap driver for zt# Ethernet tap device
+
+		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
+		Utils::snprintf(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]);
+		Utils::snprintf(mtustr,sizeof(mtustr),"%u",_mtu);
+		Utils::snprintf(metstr,sizeof(metstr),"%u",_metric);
+		long cpid = (long)vfork();
+		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;
+
+	devmap[nwids] = _dev;
+	OSUtils::writeFile((_homePath + ZT_PATH_SEPARATOR_S + "devicemap").c_str(),devmap.toString());
+
+	_thread = Thread::start(this);
+}
+
+OSXEthernetTap::~OSXEthernetTap()
+{
+	Mutex::Lock _gl(globalTapCreateLock);
+
+	::write(_shutdownSignalPipe[1],(const void *)this,1); // writing a byte causes thread to exit
+	Thread::join(_thread);
+
+	::close(_fd);
+	::close(_shutdownSignalPipe[0]);
+	::close(_shutdownSignalPipe[1]);
+
+	if (_utun) {
+		delete _arp;
+	} else {
+		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)vfork();
+			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 OSXEthernetTap::setEnabled(bool en)
+{
+	_enabled = en;
+	// TODO: interface status change
+}
+
+bool OSXEthernetTap::enabled() const
+{
+	return _enabled;
+}
+
+static bool ___removeIp(const std::string &_dev,const InetAddress &ip)
+{
+	long cpid = (long)vfork();
+	if (cpid == 0) {
+		execl("/sbin/ifconfig","/sbin/ifconfig",_dev.c_str(),"inet",ip.toIpString().c_str(),"-alias",(const char *)0);
+		_exit(-1);
+	} else if (cpid > 0) {
+		int exitcode = -1;
+		waitpid(cpid,&exitcode,0);
+		return (exitcode == 0);
+	}
+	return false; // never reached, make compiler shut up about return value
+}
+
+bool OSXEthernetTap::addIp(const InetAddress &ip)
+{
+	if (!ip)
+		return false;
+
+	std::vector<InetAddress> allIps(ips());
+	if (std::binary_search(allIps.begin(),allIps.end(),ip))
+		return true;
+
+	// Remove and reconfigure if address is the same but netmask is different
+	for(std::vector<InetAddress>::iterator i(allIps.begin());i!=allIps.end();++i) {
+		if ((i->ipsEqual(ip))&&(i->netmaskBits() != ip.netmaskBits())) {
+			if (___removeIp(_dev,*i))
+				break;
+		}
+	}
+
+	if (_utun) {
+		long cpid = (long)vfork();
+		if (cpid == 0) {
+			if (ip.ss_family == AF_INET6) {
+				::execl("/sbin/ifconfig","/sbin/ifconfig",_dev.c_str(),"inet6",ip.toString().c_str(),"alias",(const char *)0);
+			} else {
+				::execl("/sbin/ifconfig","/sbin/ifconfig",_dev.c_str(),ip.toString().c_str(),ip.toIpString().c_str(),"alias",(const char *)0);
+			}
+			::_exit(-1);
+		} else if (cpid > 0) {
+			int exitcode = -1;
+			::waitpid(cpid,&exitcode,0);
+
+			if (exitcode == 0) {
+				if (ip.ss_family == AF_INET) {
+					// Add route to network over tun for IPv4 -- otherwise it behaves
+					// as a simple point to point tunnel instead of a true route.
+					cpid = (long)vfork();
+					if (cpid == 0) {
+						::close(STDERR_FILENO);
+						::close(STDOUT_FILENO);
+						::execl("/sbin/route","/sbin/route","add",ip.network().toString().c_str(),ip.toIpString().c_str(),(const char *)0);
+						::exit(-1);
+					} else if (cpid > 0) {
+						int exitcode = -1;
+						::waitpid(cpid,&exitcode,0);
+						return (exitcode == 0);
+					}
+				} else return true;
+			}
+		}
+	} else {
+		long cpid = (long)vfork();
+		if (cpid == 0) {
+			::execl("/sbin/ifconfig","/sbin/ifconfig",_dev.c_str(),ip.isV4() ? "inet" : "inet6",ip.toString().c_str(),"alias",(const char *)0);
+			::_exit(-1);
+		} else if (cpid > 0) {
+			int exitcode = -1;
+			::waitpid(cpid,&exitcode,0);
+			return (exitcode == 0);
+		}
+	}
+
+	return false;
+}
+
+bool OSXEthernetTap::removeIp(const InetAddress &ip)
+{
+	if (!ip)
+		return true;
+	std::vector<InetAddress> allIps(ips());
+	if (!std::binary_search(allIps.begin(),allIps.end(),ip)) {
+		if (___removeIp(_dev,ip))
+			return true;
+	}
+	return false;
+}
+
+std::vector<InetAddress> OSXEthernetTap::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());
+	std::unique(r.begin(),r.end());
+
+	return r;
+}
+
+void OSXEthernetTap::put(const MAC &from,const MAC &to,unsigned int etherType,const void *data,unsigned int len)
+{
+	char putBuf[4096];
+	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 OSXEthernetTap::deviceName() const
+{
+	return _dev;
+}
+
+void OSXEthernetTap::setFriendlyName(const char *friendlyName)
+{
+}
+
+void OSXEthernetTap::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 OSXEthernetTap::threadMain()
+	throw()
+{
+	fd_set readfds,nullfds;
+	MAC to,from;
+	int n,nfds,r;
+	char getBuf[8194];
+
+	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,_nwid,from,to,etherType,0,(const void *)(getBuf + 14),r - 14);
+					}
+
+					r = 0;
+				}
+			}
+		}
+	}
+}
+
+} // namespace ZeroTier
diff --git a/attic/OSXEthernetTap.hpp.utun-work-in-progress b/attic/OSXEthernetTap.hpp.utun-work-in-progress
new file mode 100644
index 000000000..8ece87b31
--- /dev/null
+++ b/attic/OSXEthernetTap.hpp.utun-work-in-progress
@@ -0,0 +1,101 @@
+/*
+ * ZeroTier One - Network Virtualization Everywhere
+ * Copyright (C) 2011-2015  ZeroTier, Inc.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * --
+ *
+ * ZeroTier may be used and distributed under the terms of the GPLv3, which
+ * are available at: http://www.gnu.org/licenses/gpl-3.0.html
+ *
+ * If you would like to embed ZeroTier into a commercial application or
+ * redistribute it in a modified binary form, please contact ZeroTier Networks
+ * LLC. Start here: http://www.zerotier.com/
+ */
+
+#ifndef ZT_OSXETHERNETTAP_HPP
+#define ZT_OSXETHERNETTAP_HPP
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#include <stdexcept>
+#include <string>
+#include <vector>
+
+#include "../node/Constants.hpp"
+#include "../node/MAC.hpp"
+#include "../node/InetAddress.hpp"
+#include "../node/MulticastGroup.hpp"
+
+#include "Thread.hpp"
+
+namespace ZeroTier {
+
+class Arp;
+
+/**
+ * OSX Ethernet tap supporting either ZeroTier tun/tap kext or OSX-native utun
+ */
+class OSXEthernetTap
+{
+public:
+	OSXEthernetTap(
+		const char *homePath,
+		const MAC &mac,
+		unsigned int mtu,
+		unsigned int metric,
+		uint64_t nwid,
+		const char *friendlyName,
+		void (*handler)(void *,uint64_t,const MAC &,const MAC &,unsigned int,unsigned int,const void *,unsigned int),
+		void *arg);
+
+	~OSXEthernetTap();
+
+	void setEnabled(bool en);
+	bool enabled() const;
+	bool addIp(const InetAddress &ip);
+	bool removeIp(const InetAddress &ip);
+	std::vector<InetAddress> ips() const;
+	void put(const MAC &from,const MAC &to,unsigned int etherType,const void *data,unsigned int len);
+	std::string deviceName() const;
+	void setFriendlyName(const char *friendlyName);
+	void scanMulticastGroups(std::vector<MulticastGroup> &added,std::vector<MulticastGroup> &removed);
+
+	inline bool isNativeUtun() const { return _utun; }
+
+	void threadMain()
+		throw();
+
+private:
+	void (*_handler)(void *,uint64_t,const MAC &,const MAC &,unsigned int,unsigned int,const void *,unsigned int);
+	void *_arg;
+	Arp *_arp; // created and used if utun is enabled
+	uint64_t _nwid;
+	Thread _thread;
+	std::string _homePath;
+	std::string _dev;
+	std::vector<MulticastGroup> _multicastGroups;
+	unsigned int _mtu;
+	unsigned int _metric;
+	int _fd;
+	int _shutdownSignalPipe[2];
+	bool _utun;
+	volatile bool _enabled;
+};
+
+} // namespace ZeroTier
+
+#endif
diff --git a/node/InetAddress.cpp b/node/InetAddress.cpp
index abb46240f..f35eb9c33 100644
--- a/node/InetAddress.cpp
+++ b/node/InetAddress.cpp
@@ -234,7 +234,6 @@ void InetAddress::fromString(const std::string &ipSlashPort)
 }
 
 InetAddress InetAddress::netmask() const
-	throw()
 {
 	InetAddress r(*this);
 	switch(r.ss_family) {
@@ -242,36 +241,40 @@ InetAddress InetAddress::netmask() const
 			reinterpret_cast<struct sockaddr_in *>(&r)->sin_addr.s_addr = Utils::hton((uint32_t)(0xffffffff << (32 - netmaskBits())));
 			break;
 		case AF_INET6: {
-			unsigned char *bf = reinterpret_cast<unsigned char *>(reinterpret_cast<struct sockaddr_in6 *>(&r)->sin6_addr.s6_addr);
-			signed int bitsLeft = (signed int)netmaskBits();
-			for(unsigned int i=0;i<16;++i) {
-				if (bitsLeft > 0) {
-					bf[i] |= (unsigned char)((bitsLeft >= 8) ? 0x00 : (0xff >> bitsLeft));
-					bitsLeft -= 8;
-				}
-			}
+			uint64_t nm[2];
+			const unsigned int bits = netmaskBits();
+			nm[0] = Utils::hton((uint64_t)((bits >= 64) ? 0xffffffffffffffffULL : (0xffffffffffffffffULL << (64 - bits))));
+			nm[1] = Utils::hton((uint64_t)((bits <= 64) ? 0ULL : (0xffffffffffffffffULL << (128 - bits))));
+			memcpy(reinterpret_cast<struct sockaddr_in6 *>(&r)->sin6_addr.s6_addr,nm,16);
 		}	break;
 	}
 	return r;
 }
 
 InetAddress InetAddress::broadcast() const
-	throw()
+{
+	if (ss_family == AF_INET) {
+		InetAddress r(*this);
+		reinterpret_cast<struct sockaddr_in *>(&r)->sin_addr.s_addr |= Utils::hton((uint32_t)(0xffffffff >> netmaskBits()));
+		return r;
+	}
+	return InetAddress();
+}
+
+InetAddress InetAddress::network() const
 {
 	InetAddress r(*this);
 	switch(r.ss_family) {
 		case AF_INET:
-			reinterpret_cast<struct sockaddr_in *>(&r)->sin_addr.s_addr |= Utils::hton((uint32_t)(0xffffffff >> netmaskBits()));
+			reinterpret_cast<struct sockaddr_in *>(&r)->sin_addr.s_addr &= Utils::hton((uint32_t)(0xffffffff << (32 - netmaskBits())));
 			break;
 		case AF_INET6: {
-			unsigned char *bf = reinterpret_cast<unsigned char *>(reinterpret_cast<struct sockaddr_in6 *>(&r)->sin6_addr.s6_addr);
-			signed int bitsLeft = (signed int)netmaskBits();
-			for(unsigned int i=0;i<16;++i) {
-				if (bitsLeft > 0) {
-					bf[i] |= (unsigned char)((bitsLeft >= 8) ? 0x00 : (0xff >> bitsLeft));
-					bitsLeft -= 8;
-				}
-			}
+			uint64_t nm[2];
+			const unsigned int bits = netmaskBits();
+			memcpy(nm,reinterpret_cast<struct sockaddr_in6 *>(&r)->sin6_addr.s6_addr,16);
+			nm[0] &= Utils::hton((uint64_t)((bits >= 64) ? 0xffffffffffffffffULL : (0xffffffffffffffffULL << (64 - bits))));
+			nm[1] &= Utils::hton((uint64_t)((bits <= 64) ? 0ULL : (0xffffffffffffffffULL << (128 - bits))));
+			memcpy(reinterpret_cast<struct sockaddr_in6 *>(&r)->sin6_addr.s6_addr,nm,16);
 		}	break;
 	}
 	return r;
diff --git a/node/InetAddress.hpp b/node/InetAddress.hpp
index 74efc9438..2573e6941 100644
--- a/node/InetAddress.hpp
+++ b/node/InetAddress.hpp
@@ -303,17 +303,27 @@ struct InetAddress : public sockaddr_storage
 
 	/**
 	 * Construct a full netmask as an InetAddress
+	 *
+	 * @return Netmask such as 255.255.255.0 if this address is /24 (port field will be unchanged)
 	 */
-	InetAddress netmask() const
-		throw();
+	InetAddress netmask() const;
 
 	/**
 	 * Constructs a broadcast address from a network/netmask address
 	 *
+	 * This is only valid for IPv4 and will return a NULL InetAddress for other
+	 * address families.
+	 *
 	 * @return Broadcast address (only IP portion is meaningful)
 	 */
-	InetAddress broadcast() const
-		throw();
+	InetAddress broadcast() const;
+
+	/**
+	 * Return the network -- a.k.a. the IP ANDed with the netmask
+	 *
+	 * @return Network e.g. 10.0.1.0/24 from 10.0.1.200/24
+	 */
+	InetAddress network() const;
 
 	/**
 	 * @return True if this is an IPv4 address