/*
 * ZeroTier One - Network Virtualization Everywhere
 * Copyright (C) 2011-2016  ZeroTier, Inc.  https://www.zerotier.com/
 *
 * 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/>.
 */

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#include "../version.h"
#include "../include/ZeroTierOne.h"

#include "Constants.hpp"
#include "RuntimeEnvironment.hpp"
#include "IncomingPacket.hpp"
#include "Topology.hpp"
#include "Switch.hpp"
#include "Peer.hpp"
#include "NetworkController.hpp"
#include "SelfAwareness.hpp"
#include "Salsa20.hpp"
#include "SHA512.hpp"
#include "World.hpp"
#include "Cluster.hpp"
#include "Node.hpp"
#include "CertificateOfMembership.hpp"
#include "Capability.hpp"
#include "Tag.hpp"

namespace ZeroTier {

bool IncomingPacket::tryDecode(const RuntimeEnvironment *RR)
{
	const Address sourceAddress(source());

	try {
		// Check for trusted paths or unencrypted HELLOs (HELLO is the only packet sent in the clear)
		const unsigned int c = cipher();
		bool trusted = false;
		if (c == ZT_PROTO_CIPHER_SUITE__NO_CRYPTO_TRUSTED_PATH) {
			// If this is marked as a packet via a trusted path, check source address and path ID.
			// Obviously if no trusted paths are configured this always returns false and such
			// packets are dropped on the floor.
			if (RR->topology->shouldInboundPathBeTrusted(_remoteAddress,trustedPathId())) {
				trusted = true;
				TRACE("TRUSTED PATH packet approved from %s(%s), trusted path ID %llx",sourceAddress.toString().c_str(),_remoteAddress.toString().c_str(),trustedPathId());
			} else {
				TRACE("dropped packet from %s(%s), cipher set to trusted path mode but path %llx@%s is not trusted!",sourceAddress.toString().c_str(),_remoteAddress.toString().c_str(),trustedPathId(),_remoteAddress.toString().c_str());
				return true;
			}
		} else if ((c == ZT_PROTO_CIPHER_SUITE__C25519_POLY1305_NONE)&&(verb() == Packet::VERB_HELLO)) {
			// A null pointer for peer to _doHELLO() tells it to run its own
			// special internal authentication logic. This is done for unencrypted
			// HELLOs to learn new identities, etc.
			SharedPtr<Peer> tmp;
			return _doHELLO(RR,tmp);
		}

		SharedPtr<Peer> peer(RR->topology->getPeer(sourceAddress));
		if (peer) {
			if (!trusted) {
				if (!dearmor(peer->key())) {
					TRACE("dropped packet from %s(%s), MAC authentication failed (size: %u)",sourceAddress.toString().c_str(),_remoteAddress.toString().c_str(),size());
					return true;
				}
			}

			if (!uncompress()) {
				TRACE("dropped packet from %s(%s), compressed data invalid",sourceAddress.toString().c_str(),_remoteAddress.toString().c_str());
				return true;
			}

			const Packet::Verb v = verb();
			//TRACE("<< %s from %s(%s)",Packet::verbString(v),sourceAddress.toString().c_str(),_remoteAddress.toString().c_str());
			switch(v) {
				//case Packet::VERB_NOP:
				default: // ignore unknown verbs, but if they pass auth check they are "received"
					peer->received(_localAddress,_remoteAddress,hops(),packetId(),v,0,Packet::VERB_NOP);
					return true;

				case Packet::VERB_HELLO:                          return _doHELLO(RR,peer);
				case Packet::VERB_ERROR:                          return _doERROR(RR,peer);
				case Packet::VERB_OK:                             return _doOK(RR,peer);
				case Packet::VERB_WHOIS:                          return _doWHOIS(RR,peer);
				case Packet::VERB_RENDEZVOUS:                     return _doRENDEZVOUS(RR,peer);
				case Packet::VERB_FRAME:                          return _doFRAME(RR,peer);
				case Packet::VERB_EXT_FRAME:                      return _doEXT_FRAME(RR,peer);
				case Packet::VERB_ECHO:                           return _doECHO(RR,peer);
				case Packet::VERB_MULTICAST_LIKE:                 return _doMULTICAST_LIKE(RR,peer);
				case Packet::VERB_NETWORK_CREDENTIALS:            return _doNETWORK_CREDENTIALS(RR,peer);
				case Packet::VERB_NETWORK_CONFIG_REQUEST:         return _doNETWORK_CONFIG_REQUEST(RR,peer);
				case Packet::VERB_NETWORK_CONFIG_REFRESH:         return _doNETWORK_CONFIG_REFRESH(RR,peer);
				case Packet::VERB_MULTICAST_GATHER:               return _doMULTICAST_GATHER(RR,peer);
				case Packet::VERB_MULTICAST_FRAME:                return _doMULTICAST_FRAME(RR,peer);
				case Packet::VERB_PUSH_DIRECT_PATHS:              return _doPUSH_DIRECT_PATHS(RR,peer);
				case Packet::VERB_CIRCUIT_TEST:                   return _doCIRCUIT_TEST(RR,peer);
				case Packet::VERB_CIRCUIT_TEST_REPORT:            return _doCIRCUIT_TEST_REPORT(RR,peer);
				case Packet::VERB_REQUEST_PROOF_OF_WORK:          return _doREQUEST_PROOF_OF_WORK(RR,peer);
			}
		} else {
			RR->sw->requestWhois(sourceAddress);
			return false;
		}
	} catch ( ... ) {
		// Exceptions are more informatively caught in _do...() handlers but
		// this outer try/catch will catch anything else odd.
		TRACE("dropped ??? from %s(%s): unexpected exception in tryDecode()",sourceAddress.toString().c_str(),_remoteAddress.toString().c_str());
		return true;
	}
}

bool IncomingPacket::_doERROR(const RuntimeEnvironment *RR,const SharedPtr<Peer> &peer)
{
	try {
		const Packet::Verb inReVerb = (Packet::Verb)(*this)[ZT_PROTO_VERB_ERROR_IDX_IN_RE_VERB];
		const uint64_t inRePacketId = at<uint64_t>(ZT_PROTO_VERB_ERROR_IDX_IN_RE_PACKET_ID);
		const Packet::ErrorCode errorCode = (Packet::ErrorCode)(*this)[ZT_PROTO_VERB_ERROR_IDX_ERROR_CODE];

		//TRACE("ERROR %s from %s(%s) in-re %s",Packet::errorString(errorCode),peer->address().toString().c_str(),_remoteAddress.toString().c_str(),Packet::verbString(inReVerb));

		switch(errorCode) {

			case Packet::ERROR_OBJ_NOT_FOUND:
				if (inReVerb == Packet::VERB_NETWORK_CONFIG_REQUEST) {
					SharedPtr<Network> network(RR->node->network(at<uint64_t>(ZT_PROTO_VERB_ERROR_IDX_PAYLOAD)));
					if ((network)&&(network->controller() == peer->address()))
						network->setNotFound();
				}
				break;

			case Packet::ERROR_UNSUPPORTED_OPERATION:
				if (inReVerb == Packet::VERB_NETWORK_CONFIG_REQUEST) {
					SharedPtr<Network> network(RR->node->network(at<uint64_t>(ZT_PROTO_VERB_ERROR_IDX_PAYLOAD)));
					if ((network)&&(network->controller() == peer->address()))
						network->setNotFound();
				}
				break;

			case Packet::ERROR_IDENTITY_COLLISION:
				if (RR->topology->isRoot(peer->identity()))
					RR->node->postEvent(ZT_EVENT_FATAL_ERROR_IDENTITY_COLLISION);
				break;

			case Packet::ERROR_NETWORK_ACCESS_DENIED_: {
				SharedPtr<Network> network(RR->node->network(at<uint64_t>(ZT_PROTO_VERB_ERROR_IDX_PAYLOAD)));
				if ((network)&&(network->controller() == peer->address()))
					network->setAccessDenied();
			}	break;

			case Packet::ERROR_UNWANTED_MULTICAST: {
				uint64_t nwid = at<uint64_t>(ZT_PROTO_VERB_ERROR_IDX_PAYLOAD);
				MulticastGroup mg(MAC(field(ZT_PROTO_VERB_ERROR_IDX_PAYLOAD + 8,6),6),at<uint32_t>(ZT_PROTO_VERB_ERROR_IDX_PAYLOAD + 14));
				TRACE("%.16llx: peer %s unsubscrubed from multicast group %s",nwid,peer->address().toString().c_str(),mg.toString().c_str());
				RR->mc->remove(nwid,mg,peer->address());
			}	break;

			default: break;
		}

		peer->received(_localAddress,_remoteAddress,hops(),packetId(),Packet::VERB_ERROR,inRePacketId,inReVerb);
	} catch ( ... ) {
		TRACE("dropped ERROR from %s(%s): unexpected exception",peer->address().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

bool IncomingPacket::_doHELLO(const RuntimeEnvironment *RR,SharedPtr<Peer> &peer)
{
	/* Note: this is the only packet ever sent in the clear, and it's also
	 * the only packet that we authenticate via a different path. Authentication
	 * occurs here and is based on the validity of the identity and the
	 * integrity of the packet's MAC, but it must be done after we check
	 * the identity since HELLO is a mechanism for learning new identities
	 * in the first place. */

	try {
		const uint64_t pid = packetId();
		const Address fromAddress(source());
		const unsigned int protoVersion = (*this)[ZT_PROTO_VERB_HELLO_IDX_PROTOCOL_VERSION];
		const unsigned int vMajor = (*this)[ZT_PROTO_VERB_HELLO_IDX_MAJOR_VERSION];
		const unsigned int vMinor = (*this)[ZT_PROTO_VERB_HELLO_IDX_MINOR_VERSION];
		const unsigned int vRevision = at<uint16_t>(ZT_PROTO_VERB_HELLO_IDX_REVISION);
		const uint64_t timestamp = at<uint64_t>(ZT_PROTO_VERB_HELLO_IDX_TIMESTAMP);

		Identity id;
		InetAddress externalSurfaceAddress;
		uint64_t worldId = ZT_WORLD_ID_NULL;
		uint64_t worldTimestamp = 0;
		{
			unsigned int ptr = ZT_PROTO_VERB_HELLO_IDX_IDENTITY + id.deserialize(*this,ZT_PROTO_VERB_HELLO_IDX_IDENTITY);

			// Get external surface address if present (was not in old versions)
			if (ptr < size())
				ptr += externalSurfaceAddress.deserialize(*this,ptr);

			// Get world ID and world timestamp if present (was not in old versions)
			if ((ptr + 16) <= size()) {
				worldId = at<uint64_t>(ptr); ptr += 8;
				worldTimestamp = at<uint64_t>(ptr);
			}
		}

		if (protoVersion < ZT_PROTO_VERSION_MIN) {
			TRACE("dropped HELLO from %s(%s): protocol version too old",id.address().toString().c_str(),_remoteAddress.toString().c_str());
			return true;
		}
		if (fromAddress != id.address()) {
			TRACE("dropped HELLO from %s(%s): identity not for sending address",fromAddress.toString().c_str(),_remoteAddress.toString().c_str());
			return true;
		}

		if (!peer) { // peer == NULL is the normal case here
			peer = RR->topology->getPeer(id.address());
			if (peer) {
				// We already have an identity with this address -- check for collisions

				if (peer->identity() != id) {
					// Identity is different from the one we already have -- address collision

					unsigned char key[ZT_PEER_SECRET_KEY_LENGTH];
					if (RR->identity.agree(id,key,ZT_PEER_SECRET_KEY_LENGTH)) {
						if (dearmor(key)) { // ensure packet is authentic, otherwise drop
							TRACE("rejected HELLO from %s(%s): address already claimed",id.address().toString().c_str(),_remoteAddress.toString().c_str());
							Packet outp(id.address(),RR->identity.address(),Packet::VERB_ERROR);
							outp.append((unsigned char)Packet::VERB_HELLO);
							outp.append((uint64_t)pid);
							outp.append((unsigned char)Packet::ERROR_IDENTITY_COLLISION);
							outp.armor(key,true);
							RR->node->putPacket(_localAddress,_remoteAddress,outp.data(),outp.size());
						} else {
							TRACE("rejected HELLO from %s(%s): packet failed authentication",id.address().toString().c_str(),_remoteAddress.toString().c_str());
						}
					} else {
						TRACE("rejected HELLO from %s(%s): key agreement failed",id.address().toString().c_str(),_remoteAddress.toString().c_str());
					}

					return true;
				} else {
					// Identity is the same as the one we already have -- check packet integrity

					if (!dearmor(peer->key())) {
						TRACE("rejected HELLO from %s(%s): packet failed authentication",id.address().toString().c_str(),_remoteAddress.toString().c_str());
						return true;
					}

					// Continue at // VALID
				}
			} else {
				// We don't already have an identity with this address -- validate and learn it

				// Check identity proof of work
				if (!id.locallyValidate()) {
					TRACE("dropped HELLO from %s(%s): identity invalid",id.address().toString().c_str(),_remoteAddress.toString().c_str());
					return true;
				}

				// Check packet integrity and authentication
				SharedPtr<Peer> newPeer(new Peer(RR,RR->identity,id));
				if (!dearmor(newPeer->key())) {
					TRACE("rejected HELLO from %s(%s): packet failed authentication",id.address().toString().c_str(),_remoteAddress.toString().c_str());
					return true;
				}
				peer = RR->topology->addPeer(newPeer);

				// Continue at // VALID
			}

			// VALID -- if we made it here, packet passed identity and authenticity checks!
		}

		if (externalSurfaceAddress)
			RR->sa->iam(id.address(),_localAddress,_remoteAddress,externalSurfaceAddress,RR->topology->isUpstream(id),RR->node->now());

		Packet outp(id.address(),RR->identity.address(),Packet::VERB_OK);
		outp.append((unsigned char)Packet::VERB_HELLO);
		outp.append((uint64_t)pid);
		outp.append((uint64_t)timestamp);
		outp.append((unsigned char)ZT_PROTO_VERSION);
		outp.append((unsigned char)ZEROTIER_ONE_VERSION_MAJOR);
		outp.append((unsigned char)ZEROTIER_ONE_VERSION_MINOR);
		outp.append((uint16_t)ZEROTIER_ONE_VERSION_REVISION);
		if (protoVersion >= 5) {
			_remoteAddress.serialize(outp);
		} else {
			/* LEGACY COMPATIBILITY HACK:
			 *
			 * For a while now (since 1.0.3), ZeroTier has recognized changes in
			 * its network environment empirically by examining its external network
			 * address as reported by trusted peers. In versions prior to 1.1.0
			 * (protocol version < 5), they did this by saving a snapshot of this
			 * information (in SelfAwareness.hpp) keyed by reporting device ID and
			 * address type.
			 *
			 * This causes problems when clustering is combined with symmetric NAT.
			 * Symmetric NAT remaps ports, so different endpoints in a cluster will
			 * report back different exterior addresses. Since the old code keys
			 * this by device ID and not sending physical address and compares the
			 * entire address including port, it constantly thinks its external
			 * surface is changing and resets connections when talking to a cluster.
			 *
			 * In new code we key by sending physical address and device and we also
			 * take the more conservative position of only interpreting changes in
			 * IP address (neglecting port) as a change in network topology that
			 * necessitates a reset. But we can make older clients work here by
			 * nulling out the port field. Since this info is only used for empirical
			 * detection of link changes, it doesn't break anything else.
			 */
			InetAddress tmpa(_remoteAddress);
			tmpa.setPort(0);
			tmpa.serialize(outp);
		}

		if ((worldId != ZT_WORLD_ID_NULL)&&(RR->topology->worldTimestamp() > worldTimestamp)&&(worldId == RR->topology->worldId())) {
			World w(RR->topology->world());
			const unsigned int sizeAt = outp.size();
			outp.addSize(2); // make room for 16-bit size field
			w.serialize(outp,false);
			outp.setAt<uint16_t>(sizeAt,(uint16_t)(outp.size() - (sizeAt + 2)));
		} else {
			outp.append((uint16_t)0); // no world update needed
		}

		outp.armor(peer->key(),true);
		RR->node->putPacket(_localAddress,_remoteAddress,outp.data(),outp.size());

		peer->setRemoteVersion(protoVersion,vMajor,vMinor,vRevision); // important for this to go first so received() knows the version
		peer->received(_localAddress,_remoteAddress,hops(),pid,Packet::VERB_HELLO,0,Packet::VERB_NOP);
	} catch ( ... ) {
		TRACE("dropped HELLO from %s(%s): unexpected exception",source().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

bool IncomingPacket::_doOK(const RuntimeEnvironment *RR,const SharedPtr<Peer> &peer)
{
	try {
		const Packet::Verb inReVerb = (Packet::Verb)(*this)[ZT_PROTO_VERB_OK_IDX_IN_RE_VERB];
		const uint64_t inRePacketId = at<uint64_t>(ZT_PROTO_VERB_OK_IDX_IN_RE_PACKET_ID);

		//TRACE("%s(%s): OK(%s)",source().toString().c_str(),_remoteAddress.toString().c_str(),Packet::verbString(inReVerb));

		switch(inReVerb) {

			case Packet::VERB_HELLO: {
				const unsigned int latency = std::min((unsigned int)(RR->node->now() - at<uint64_t>(ZT_PROTO_VERB_HELLO__OK__IDX_TIMESTAMP)),(unsigned int)0xffff);
				const unsigned int vProto = (*this)[ZT_PROTO_VERB_HELLO__OK__IDX_PROTOCOL_VERSION];
				const unsigned int vMajor = (*this)[ZT_PROTO_VERB_HELLO__OK__IDX_MAJOR_VERSION];
				const unsigned int vMinor = (*this)[ZT_PROTO_VERB_HELLO__OK__IDX_MINOR_VERSION];
				const unsigned int vRevision = at<uint16_t>(ZT_PROTO_VERB_HELLO__OK__IDX_REVISION);

				if (vProto < ZT_PROTO_VERSION_MIN) {
					TRACE("%s(%s): OK(HELLO) dropped, protocol version too old",source().toString().c_str(),_remoteAddress.toString().c_str());
					return true;
				}

				InetAddress externalSurfaceAddress;
				unsigned int ptr = ZT_PROTO_VERB_HELLO__OK__IDX_REVISION + 2;

				// Get reported external surface address if present (was not on old versions)
				if (ptr < size())
					ptr += externalSurfaceAddress.deserialize(*this,ptr);

				// Handle world updates from root servers if present (was not on old versions)
				if (((ptr + 2) <= size())&&(RR->topology->isRoot(peer->identity()))) {
					World worldUpdate;
					const unsigned int worldLen = at<uint16_t>(ptr); ptr += 2;
					if (worldLen > 0) {
						World w;
						w.deserialize(*this,ptr);
						RR->topology->worldUpdateIfValid(w);
					}
				}

				TRACE("%s(%s): OK(HELLO), version %u.%u.%u, latency %u, reported external address %s",source().toString().c_str(),_remoteAddress.toString().c_str(),vMajor,vMinor,vRevision,latency,((externalSurfaceAddress) ? externalSurfaceAddress.toString().c_str() : "(none)"));

				peer->addDirectLatencyMeasurment(latency);
				peer->setRemoteVersion(vProto,vMajor,vMinor,vRevision);

				if (externalSurfaceAddress)
					RR->sa->iam(peer->address(),_localAddress,_remoteAddress,externalSurfaceAddress,RR->topology->isUpstream(peer->identity()),RR->node->now());
			}	break;

			case Packet::VERB_WHOIS: {
				if (RR->topology->isUpstream(peer->identity())) {
					const Identity id(*this,ZT_PROTO_VERB_WHOIS__OK__IDX_IDENTITY);
					RR->sw->doAnythingWaitingForPeer(RR->topology->addPeer(SharedPtr<Peer>(new Peer(RR,RR->identity,id))));
				}
			} break;

			case Packet::VERB_NETWORK_CONFIG_REQUEST: {
				const uint64_t nwid = at<uint64_t>(ZT_PROTO_VERB_NETWORK_CONFIG_REQUEST__OK__IDX_NETWORK_ID);
				const SharedPtr<Network> network(RR->node->network(nwid));
				if ((network)&&(network->controller() == peer->address())) {
					const unsigned int chunkLen = at<uint16_t>(ZT_PROTO_VERB_NETWORK_CONFIG_REQUEST__OK__IDX_DICT_LEN);
					const void *chunkData = field(ZT_PROTO_VERB_NETWORK_CONFIG_REQUEST__OK__IDX_DICT,chunkLen);
					unsigned int chunkIndex = 0;
					unsigned int totalSize = chunkLen;
					if ((ZT_PROTO_VERB_NETWORK_CONFIG_REQUEST__OK__IDX_DICT + chunkLen) < size()) {
						totalSize = at<uint32_t>(ZT_PROTO_VERB_NETWORK_CONFIG_REQUEST__OK__IDX_DICT + chunkLen);
						chunkIndex = at<uint32_t>(ZT_PROTO_VERB_NETWORK_CONFIG_REQUEST__OK__IDX_DICT + chunkLen + 4);
					}
					TRACE("%s(%s): OK(NETWORK_CONFIG_REQUEST) chunkLen==%u chunkIndex==%u totalSize==%u",source().toString().c_str(),_remoteAddress.toString().c_str(),chunkLen,chunkIndex,totalSize);
					network->handleInboundConfigChunk(inRePacketId,chunkData,chunkLen,chunkIndex,totalSize);
				}
			}	break;

			//case Packet::VERB_ECHO: {
			//}	break;

			case Packet::VERB_MULTICAST_GATHER: {
				const uint64_t nwid = at<uint64_t>(ZT_PROTO_VERB_MULTICAST_GATHER__OK__IDX_NETWORK_ID);
				const MulticastGroup mg(MAC(field(ZT_PROTO_VERB_MULTICAST_GATHER__OK__IDX_MAC,6),6),at<uint32_t>(ZT_PROTO_VERB_MULTICAST_GATHER__OK__IDX_ADI));
				//TRACE("%s(%s): OK(MULTICAST_GATHER) %.16llx/%s length %u",source().toString().c_str(),_remoteAddress.toString().c_str(),nwid,mg.toString().c_str(),size());
				const unsigned int count = at<uint16_t>(ZT_PROTO_VERB_MULTICAST_GATHER__OK__IDX_GATHER_RESULTS + 4);
				RR->mc->addMultiple(RR->node->now(),nwid,mg,field(ZT_PROTO_VERB_MULTICAST_GATHER__OK__IDX_GATHER_RESULTS + 6,count * 5),count,at<uint32_t>(ZT_PROTO_VERB_MULTICAST_GATHER__OK__IDX_GATHER_RESULTS));
			}	break;

			case Packet::VERB_MULTICAST_FRAME: {
				const unsigned int flags = (*this)[ZT_PROTO_VERB_MULTICAST_FRAME__OK__IDX_FLAGS];
				const uint64_t nwid = at<uint64_t>(ZT_PROTO_VERB_MULTICAST_FRAME__OK__IDX_NETWORK_ID);
				const MulticastGroup mg(MAC(field(ZT_PROTO_VERB_MULTICAST_FRAME__OK__IDX_MAC,6),6),at<uint32_t>(ZT_PROTO_VERB_MULTICAST_FRAME__OK__IDX_ADI));

				//TRACE("%s(%s): OK(MULTICAST_FRAME) %.16llx/%s flags %.2x",peer->address().toString().c_str(),_remoteAddress.toString().c_str(),nwid,mg.toString().c_str(),flags);

				unsigned int offset = 0;

				if ((flags & 0x01) != 0) { // deprecated but still used by older peers
					CertificateOfMembership com;
					offset += com.deserialize(*this,ZT_PROTO_VERB_MULTICAST_FRAME__OK__IDX_COM_AND_GATHER_RESULTS);
					if (com) {
						SharedPtr<Network> network(RR->node->network(com.networkId()));
						if (network)
							network->addCredential(com);
					}
				}

				if ((flags & 0x02) != 0) {
					// OK(MULTICAST_FRAME) includes implicit gather results
					offset += ZT_PROTO_VERB_MULTICAST_FRAME__OK__IDX_COM_AND_GATHER_RESULTS;
					unsigned int totalKnown = at<uint32_t>(offset); offset += 4;
					unsigned int count = at<uint16_t>(offset); offset += 2;
					RR->mc->addMultiple(RR->node->now(),nwid,mg,field(offset,count * 5),count,totalKnown);
				}
			}	break;

			default: break;
		}

		peer->received(_localAddress,_remoteAddress,hops(),packetId(),Packet::VERB_OK,inRePacketId,inReVerb);
	} catch ( ... ) {
		TRACE("dropped OK from %s(%s): unexpected exception",source().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

bool IncomingPacket::_doWHOIS(const RuntimeEnvironment *RR,const SharedPtr<Peer> &peer)
{
	try {
		if (payloadLength() == ZT_ADDRESS_LENGTH) {
			const Address addr(payload(),ZT_ADDRESS_LENGTH);
			const Identity id(RR->topology->getIdentity(addr));
			if (id) {
				Packet outp(peer->address(),RR->identity.address(),Packet::VERB_OK);
				outp.append((unsigned char)Packet::VERB_WHOIS);
				outp.append(packetId());
				id.serialize(outp,false);
				outp.armor(peer->key(),true);
				RR->node->putPacket(_localAddress,_remoteAddress,outp.data(),outp.size());
			} else {
#ifdef ZT_ENABLE_CLUSTER
				if (RR->cluster)
					RR->cluster->sendDistributedQuery(*this);
#endif
				if (!RR->topology->amRoot()) {
					RR->sw->requestWhois(addr);
					return false; // packet parse will be attempted again if we get a reply from upstream
				}
			}
		} else {
			TRACE("dropped WHOIS from %s(%s): missing or invalid address",source().toString().c_str(),_remoteAddress.toString().c_str());
		}
		peer->received(_localAddress,_remoteAddress,hops(),packetId(),Packet::VERB_WHOIS,0,Packet::VERB_NOP);
	} catch ( ... ) {
		TRACE("dropped WHOIS from %s(%s): unexpected exception",source().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

bool IncomingPacket::_doRENDEZVOUS(const RuntimeEnvironment *RR,const SharedPtr<Peer> &peer)
{
	try {
		const Address with(field(ZT_PROTO_VERB_RENDEZVOUS_IDX_ZTADDRESS,ZT_ADDRESS_LENGTH),ZT_ADDRESS_LENGTH);
		const SharedPtr<Peer> withPeer(RR->topology->getPeer(with));
		if (withPeer) {
			const unsigned int port = at<uint16_t>(ZT_PROTO_VERB_RENDEZVOUS_IDX_PORT);
			const unsigned int addrlen = (*this)[ZT_PROTO_VERB_RENDEZVOUS_IDX_ADDRLEN];
			if ((port > 0)&&((addrlen == 4)||(addrlen == 16))) {
				const InetAddress atAddr(field(ZT_PROTO_VERB_RENDEZVOUS_IDX_ADDRESS,addrlen),addrlen,port);
				if (!RR->topology->isUpstream(peer->identity())) {
					TRACE("RENDEZVOUS from %s says %s might be at %s, ignoring since peer is not upstream",peer->address().toString().c_str(),with.toString().c_str(),atAddr.toString().c_str());
				} else if (RR->node->shouldUsePathForZeroTierTraffic(_localAddress,atAddr)) {
					const uint64_t now = RR->node->now();
					peer->sendHELLO(_localAddress,atAddr,now,2); // send low-TTL packet to 'open' local NAT(s)
					if (!peer->pushDirectPaths(_localAddress,atAddr,now,true))
						peer->sendHELLO(_localAddress,atAddr,now);
					TRACE("RENDEZVOUS from %s says %s might be at %s, sent verification attempt",peer->address().toString().c_str(),with.toString().c_str(),atAddr.toString().c_str());
				} else {
					TRACE("RENDEZVOUS from %s says %s might be at %s, ignoring since path is not suitable",peer->address().toString().c_str(),with.toString().c_str(),atAddr.toString().c_str());
				}
			} else {
				TRACE("dropped corrupt RENDEZVOUS from %s(%s) (bad address or port)",peer->address().toString().c_str(),_remoteAddress.toString().c_str());
			}
		} else {
			TRACE("ignored RENDEZVOUS from %s(%s) to meet unknown peer %s",peer->address().toString().c_str(),_remoteAddress.toString().c_str(),with.toString().c_str());
		}

		peer->received(_localAddress,_remoteAddress,hops(),packetId(),Packet::VERB_RENDEZVOUS,0,Packet::VERB_NOP);
	} catch ( ... ) {
		TRACE("dropped RENDEZVOUS from %s(%s): unexpected exception",peer->address().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

bool IncomingPacket::_doFRAME(const RuntimeEnvironment *RR,const SharedPtr<Peer> &peer)
{
	try {
		const SharedPtr<Network> network(RR->node->network(at<uint64_t>(ZT_PROTO_VERB_FRAME_IDX_NETWORK_ID)));
		if (network) {
			if (size() > ZT_PROTO_VERB_FRAME_IDX_PAYLOAD) {
				if (!network->isAllowed(peer)) {
					TRACE("dropped FRAME from %s(%s): not a member of private network %.16llx",peer->address().toString().c_str(),_remoteAddress.toString().c_str(),(unsigned long long)network->id());
					return true;
				}

				const unsigned int etherType = at<uint16_t>(ZT_PROTO_VERB_FRAME_IDX_ETHERTYPE);
				const MAC sourceMac(peer->address(),network->id());
				const unsigned int frameLen = size() - ZT_PROTO_VERB_FRAME_IDX_PAYLOAD;
				const uint8_t *const frameData = reinterpret_cast<const uint8_t *>(data()) + ZT_PROTO_VERB_FRAME_IDX_PAYLOAD;
				if (network->filterIncomingPacket(peer,RR->identity.address(),sourceMac,network->mac(),frameData,frameLen,etherType,0)) {
					RR->node->putFrame(network->id(),network->userPtr(),sourceMac,network->mac(),etherType,0,(const void *)frameData,frameLen);
				}
			}

			peer->received(_localAddress,_remoteAddress,hops(),packetId(),Packet::VERB_FRAME,0,Packet::VERB_NOP);
		} else {
			TRACE("dropped FRAME from %s(%s): we are not connected to network %.16llx",source().toString().c_str(),_remoteAddress.toString().c_str(),at<uint64_t>(ZT_PROTO_VERB_FRAME_IDX_NETWORK_ID));
		}
	} catch ( ... ) {
		TRACE("dropped FRAME from %s(%s): unexpected exception",source().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

bool IncomingPacket::_doEXT_FRAME(const RuntimeEnvironment *RR,const SharedPtr<Peer> &peer)
{
	try {
		SharedPtr<Network> network(RR->node->network(at<uint64_t>(ZT_PROTO_VERB_EXT_FRAME_IDX_NETWORK_ID)));
		if (network) {
			if (size() > ZT_PROTO_VERB_EXT_FRAME_IDX_PAYLOAD) {
				const unsigned int flags = (*this)[ZT_PROTO_VERB_EXT_FRAME_IDX_FLAGS];

				unsigned int comLen = 0;
				if ((flags & 0x01) != 0) { // deprecated but still used by old peers
					CertificateOfMembership com;
					comLen = com.deserialize(*this,ZT_PROTO_VERB_EXT_FRAME_IDX_COM);
					if (com)
						network->addCredential(com);
				}

				if (!network->isAllowed(peer)) {
					TRACE("dropped EXT_FRAME from %s(%s): not a member of private network %.16llx",peer->address().toString().c_str(),_remoteAddress.toString().c_str(),network->id());
					return true;
				}

				// Everything after flags must be adjusted based on the length
				// of the certificate, if there was one...

				const unsigned int etherType = at<uint16_t>(comLen + ZT_PROTO_VERB_EXT_FRAME_IDX_ETHERTYPE);

				const MAC to(field(comLen + ZT_PROTO_VERB_EXT_FRAME_IDX_TO,ZT_PROTO_VERB_EXT_FRAME_LEN_TO),ZT_PROTO_VERB_EXT_FRAME_LEN_TO);
				const MAC from(field(comLen + ZT_PROTO_VERB_EXT_FRAME_IDX_FROM,ZT_PROTO_VERB_EXT_FRAME_LEN_FROM),ZT_PROTO_VERB_EXT_FRAME_LEN_FROM);

				if ((!from)||(from.isMulticast())||(from == network->mac())) {
					TRACE("dropped EXT_FRAME from %s@%s(%s) to %s: invalid source MAC",from.toString().c_str(),peer->address().toString().c_str(),_remoteAddress.toString().c_str(),to.toString().c_str());
					return true;
				}

				if (from != MAC(peer->address(),network->id())) {
					if (network->config().permitsBridging(peer->address())) {
						network->learnBridgeRoute(from,peer->address());
					} else {
						TRACE("dropped EXT_FRAME from %s@%s(%s) to %s: sender not allowed to bridge into %.16llx",from.toString().c_str(),peer->address().toString().c_str(),_remoteAddress.toString().c_str(),to.toString().c_str(),network->id());
						return true;
					}
				} else if (to != network->mac()) {
					if (!network->config().permitsBridging(RR->identity.address())) {
						TRACE("dropped EXT_FRAME from %s@%s(%s) to %s: I cannot bridge to %.16llx or bridging disabled on network",from.toString().c_str(),peer->address().toString().c_str(),_remoteAddress.toString().c_str(),to.toString().c_str(),network->id());
						return true;
					}
				}

				const unsigned int frameLen = size() - (comLen + ZT_PROTO_VERB_EXT_FRAME_IDX_PAYLOAD);
				const uint8_t *const frameData = (const uint8_t *)field(comLen + ZT_PROTO_VERB_EXT_FRAME_IDX_PAYLOAD,frameLen);

				if (network->filterIncomingPacket(peer,RR->identity.address(),from,to,frameData,frameLen,etherType,0)) {
					RR->node->putFrame(network->id(),network->userPtr(),from,to,etherType,0,(const void *)frameData,frameLen);
				}
			}

			peer->received(_localAddress,_remoteAddress,hops(),packetId(),Packet::VERB_EXT_FRAME,0,Packet::VERB_NOP);
		} else {
			TRACE("dropped EXT_FRAME from %s(%s): we are not connected to network %.16llx",source().toString().c_str(),_remoteAddress.toString().c_str(),at<uint64_t>(ZT_PROTO_VERB_FRAME_IDX_NETWORK_ID));
		}
	} catch ( ... ) {
		TRACE("dropped EXT_FRAME from %s(%s): unexpected exception",source().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

bool IncomingPacket::_doECHO(const RuntimeEnvironment *RR,const SharedPtr<Peer> &peer)
{
	try {
		const uint64_t pid = packetId();
		Packet outp(peer->address(),RR->identity.address(),Packet::VERB_OK);
		outp.append((unsigned char)Packet::VERB_ECHO);
		outp.append((uint64_t)pid);
		if (size() > ZT_PACKET_IDX_PAYLOAD)
			outp.append(reinterpret_cast<const unsigned char *>(data()) + ZT_PACKET_IDX_PAYLOAD,size() - ZT_PACKET_IDX_PAYLOAD);
		outp.armor(peer->key(),true);
		RR->node->putPacket(_localAddress,_remoteAddress,outp.data(),outp.size());
		peer->received(_localAddress,_remoteAddress,hops(),pid,Packet::VERB_ECHO,0,Packet::VERB_NOP);
	} catch ( ... ) {
		TRACE("dropped ECHO from %s(%s): unexpected exception",source().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

bool IncomingPacket::_doMULTICAST_LIKE(const RuntimeEnvironment *RR,const SharedPtr<Peer> &peer)
{
	try {
		const uint64_t now = RR->node->now();

		// Iterate through 18-byte network,MAC,ADI tuples
		for(unsigned int ptr=ZT_PACKET_IDX_PAYLOAD;ptr<size();ptr+=18) {
			const uint64_t nwid = at<uint64_t>(ptr);
			const MulticastGroup group(MAC(field(ptr + 8,6),6),at<uint32_t>(ptr + 14));
			RR->mc->add(now,nwid,group,peer->address());
		}

		peer->received(_localAddress,_remoteAddress,hops(),packetId(),Packet::VERB_MULTICAST_LIKE,0,Packet::VERB_NOP);
	} catch ( ... ) {
		TRACE("dropped MULTICAST_LIKE from %s(%s): unexpected exception",source().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

bool IncomingPacket::_doNETWORK_CREDENTIALS(const RuntimeEnvironment *RR,const SharedPtr<Peer> &peer)
{
	try {
		CertificateOfMembership com;
		Capability cap;
		Tag tag;

		unsigned int p = ZT_PACKET_IDX_PAYLOAD;
		while ((p < size())&&((*this)[p])) {
			p += com.deserialize(*this,p);
			if (com) {
				SharedPtr<Network> network(RR->node->network(com.networkId()));
				if (network) {
					if (network->addCredential(com) == 1)
						return false; // wait for WHOIS
				}
			}
		}
		++p; // skip trailing 0 after COMs if present

		if (p < size()) { // check if new capabilities and tags fields are present
			const unsigned int numCapabilities = at<uint16_t>(p); p += 2;
			for(unsigned int i=0;i<numCapabilities;++i) {
				p += cap.deserialize(*this,p);
				SharedPtr<Network> network(RR->node->network(cap.networkId()));
				if (network) {
					if (network->addCredential(cap) == 1)
						return false; // wait for WHOIS
				}
			}

			const unsigned int numTags = at<uint16_t>(p); p += 2;
			for(unsigned int i=0;i<numTags;++i) {
				p += tag.deserialize(*this,p);
				SharedPtr<Network> network(RR->node->network(tag.networkId()));
				if (network) {
					if (network->addCredential(tag) == 1)
						return false; // wait for WHOIS
				}
			}
		}

		peer->received(_localAddress,_remoteAddress,hops(),packetId(),Packet::VERB_NETWORK_CREDENTIALS,0,Packet::VERB_NOP);
	} catch ( ... ) {
		TRACE("dropped NETWORK_CREDENTIALS from %s(%s): unexpected exception",source().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

bool IncomingPacket::_doNETWORK_CONFIG_REQUEST(const RuntimeEnvironment *RR,const SharedPtr<Peer> &peer)
{
	try {
		const uint64_t nwid = at<uint64_t>(ZT_PROTO_VERB_NETWORK_CONFIG_REQUEST_IDX_NETWORK_ID);

		const unsigned int metaDataLength = at<uint16_t>(ZT_PROTO_VERB_NETWORK_CONFIG_REQUEST_IDX_DICT_LEN);
		const char *metaDataBytes = (const char *)field(ZT_PROTO_VERB_NETWORK_CONFIG_REQUEST_IDX_DICT,metaDataLength);
		const Dictionary<ZT_NETWORKCONFIG_METADATA_DICT_CAPACITY> metaData(metaDataBytes,metaDataLength);

		const unsigned int hopCount = hops();
		const uint64_t requestPacketId = packetId();
		peer->received(_localAddress,_remoteAddress,hopCount,requestPacketId,Packet::VERB_NETWORK_CONFIG_REQUEST,0,Packet::VERB_NOP);

		if (RR->localNetworkController) {
			NetworkConfig *netconf = new NetworkConfig();
			try {
				switch(RR->localNetworkController->doNetworkConfigRequest((hopCount > 0) ? InetAddress() : _remoteAddress,RR->identity,peer->identity(),nwid,metaData,*netconf)) {

					case NetworkController::NETCONF_QUERY_OK: {
						Dictionary<ZT_NETWORKCONFIG_DICT_CAPACITY> *dconf = new Dictionary<ZT_NETWORKCONFIG_DICT_CAPACITY>();
						try {
							if (netconf->toDictionary(*dconf,metaData.getUI(ZT_NETWORKCONFIG_REQUEST_METADATA_KEY_VERSION,0) < 6)) {
								const unsigned int totalSize = dconf->sizeBytes();
								unsigned int chunkIndex = 0;
								while (chunkIndex < totalSize) {
									const unsigned int chunkLen = std::min(totalSize - chunkIndex,(unsigned int)(ZT_PROTO_MAX_PACKET_LENGTH - (ZT_PACKET_IDX_PAYLOAD + 32)));
									Packet outp(peer->address(),RR->identity.address(),Packet::VERB_OK);
									outp.append((unsigned char)Packet::VERB_NETWORK_CONFIG_REQUEST);
									outp.append(requestPacketId);
									outp.append(nwid);
									outp.append((uint16_t)chunkLen);
									outp.append((const void *)(dconf->data() + chunkIndex),chunkLen);
									outp.append((uint32_t)totalSize);
									outp.append((uint32_t)chunkIndex);
									outp.compress();
									RR->sw->send(outp,true);
									chunkIndex += chunkLen;
								}
							}
							delete dconf;
						} catch ( ... ) {
							delete dconf;
							throw;
						}
					}	break;

					case NetworkController::NETCONF_QUERY_OBJECT_NOT_FOUND: {
						Packet outp(peer->address(),RR->identity.address(),Packet::VERB_ERROR);
						outp.append((unsigned char)Packet::VERB_NETWORK_CONFIG_REQUEST);
						outp.append(requestPacketId);
						outp.append((unsigned char)Packet::ERROR_OBJ_NOT_FOUND);
						outp.append(nwid);
						outp.armor(peer->key(),true);
						RR->node->putPacket(_localAddress,_remoteAddress,outp.data(),outp.size());
					}	break;

					case NetworkController::NETCONF_QUERY_ACCESS_DENIED: {
						Packet outp(peer->address(),RR->identity.address(),Packet::VERB_ERROR);
						outp.append((unsigned char)Packet::VERB_NETWORK_CONFIG_REQUEST);
						outp.append(requestPacketId);
						outp.append((unsigned char)Packet::ERROR_NETWORK_ACCESS_DENIED_);
						outp.append(nwid);
						outp.armor(peer->key(),true);
						RR->node->putPacket(_localAddress,_remoteAddress,outp.data(),outp.size());
					} break;

					case NetworkController::NETCONF_QUERY_INTERNAL_SERVER_ERROR:
						break;
					case NetworkController::NETCONF_QUERY_IGNORE:
						break;
					default:
						TRACE("NETWORK_CONFIG_REQUEST failed: invalid return value from NetworkController::doNetworkConfigRequest()");
						break;
				}
				delete netconf;
			} catch ( ... ) {
				delete netconf;
				throw;
			}
		} else {
			Packet outp(peer->address(),RR->identity.address(),Packet::VERB_ERROR);
			outp.append((unsigned char)Packet::VERB_NETWORK_CONFIG_REQUEST);
			outp.append(requestPacketId);
			outp.append((unsigned char)Packet::ERROR_UNSUPPORTED_OPERATION);
			outp.append(nwid);
			outp.armor(peer->key(),true);
			RR->node->putPacket(_localAddress,_remoteAddress,outp.data(),outp.size());
		}
	} catch (std::exception &exc) {
		fprintf(stderr,"WARNING: network config request failed with exception: %s" ZT_EOL_S,exc.what());
		TRACE("dropped NETWORK_CONFIG_REQUEST from %s(%s): %s",source().toString().c_str(),_remoteAddress.toString().c_str(),exc.what());
	} catch ( ... ) {
		fprintf(stderr,"WARNING: network config request failed with exception: unknown exception" ZT_EOL_S);
		TRACE("dropped NETWORK_CONFIG_REQUEST from %s(%s): unknown exception",source().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

bool IncomingPacket::_doNETWORK_CONFIG_REFRESH(const RuntimeEnvironment *RR,const SharedPtr<Peer> &peer)
{
	try {
		unsigned int p = ZT_PACKET_IDX_PAYLOAD;
		while ((p + 8) <= size()) {
			const uint64_t nwid = at<uint64_t>(p); p += 8;
			if (Network::controllerFor(nwid) == peer->address()) {
				SharedPtr<Network> network(RR->node->network(nwid));
				if (network)
					network->requestConfiguration();
			}
		}
	} catch ( ... ) {
		TRACE("dropped NETWORK_CONFIG_REFRESH from %s(%s): unexpected exception",source().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

bool IncomingPacket::_doMULTICAST_GATHER(const RuntimeEnvironment *RR,const SharedPtr<Peer> &peer)
{
	try {
		const uint64_t nwid = at<uint64_t>(ZT_PROTO_VERB_MULTICAST_GATHER_IDX_NETWORK_ID);
		const MulticastGroup mg(MAC(field(ZT_PROTO_VERB_MULTICAST_GATHER_IDX_MAC,6),6),at<uint32_t>(ZT_PROTO_VERB_MULTICAST_GATHER_IDX_ADI));
		const unsigned int gatherLimit = at<uint32_t>(ZT_PROTO_VERB_MULTICAST_GATHER_IDX_GATHER_LIMIT);

		//TRACE("<<MC %s(%s) GATHER up to %u in %.16llx/%s",source().toString().c_str(),_remoteAddress.toString().c_str(),gatherLimit,nwid,mg.toString().c_str());

		if (gatherLimit) {
			Packet outp(peer->address(),RR->identity.address(),Packet::VERB_OK);
			outp.append((unsigned char)Packet::VERB_MULTICAST_GATHER);
			outp.append(packetId());
			outp.append(nwid);
			mg.mac().appendTo(outp);
			outp.append((uint32_t)mg.adi());
			const unsigned int gatheredLocally = RR->mc->gather(peer->address(),nwid,mg,outp,gatherLimit);
			if (gatheredLocally) {
				outp.armor(peer->key(),true);
				RR->node->putPacket(_localAddress,_remoteAddress,outp.data(),outp.size());
			}

#ifdef ZT_ENABLE_CLUSTER
			if ((RR->cluster)&&(gatheredLocally < gatherLimit))
				RR->cluster->sendDistributedQuery(*this);
#endif
		}

		peer->received(_localAddress,_remoteAddress,hops(),packetId(),Packet::VERB_MULTICAST_GATHER,0,Packet::VERB_NOP);
	} catch ( ... ) {
		TRACE("dropped MULTICAST_GATHER from %s(%s): unexpected exception",source().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

bool IncomingPacket::_doMULTICAST_FRAME(const RuntimeEnvironment *RR,const SharedPtr<Peer> &peer)
{
	try {
		const uint64_t nwid = at<uint64_t>(ZT_PROTO_VERB_MULTICAST_FRAME_IDX_NETWORK_ID);
		const unsigned int flags = (*this)[ZT_PROTO_VERB_MULTICAST_FRAME_IDX_FLAGS];

		const SharedPtr<Network> network(RR->node->network(nwid));
		if (network) {
			// Offset -- size of optional fields added to position of later fields
			unsigned int offset = 0;

			if ((flags & 0x01) != 0) { // deprecated but still used by older peers
				CertificateOfMembership com;
				offset += com.deserialize(*this,ZT_PROTO_VERB_MULTICAST_FRAME_IDX_COM);
				if (com)
					network->addCredential(com);
			}

			// Check membership after we've read any included COM, since
			// that cert might be what we needed.
			if (!network->isAllowed(peer)) {
				TRACE("dropped MULTICAST_FRAME from %s(%s): not a member of private network %.16llx",peer->address().toString().c_str(),_remoteAddress.toString().c_str(),(unsigned long long)network->id());
				return true;
			}

			unsigned int gatherLimit = 0;
			if ((flags & 0x02) != 0) {
				gatherLimit = at<uint32_t>(offset + ZT_PROTO_VERB_MULTICAST_FRAME_IDX_GATHER_LIMIT);
				offset += 4;
			}

			MAC from;
			if ((flags & 0x04) != 0) {
				from.setTo(field(offset + ZT_PROTO_VERB_MULTICAST_FRAME_IDX_SOURCE_MAC,6),6);
				offset += 6;
			} else {
				from.fromAddress(peer->address(),nwid);
			}

			const MulticastGroup to(MAC(field(offset + ZT_PROTO_VERB_MULTICAST_FRAME_IDX_DEST_MAC,6),6),at<uint32_t>(offset + ZT_PROTO_VERB_MULTICAST_FRAME_IDX_DEST_ADI));
			const unsigned int etherType = at<uint16_t>(offset + ZT_PROTO_VERB_MULTICAST_FRAME_IDX_ETHERTYPE);
			const unsigned int frameLen = size() - (offset + ZT_PROTO_VERB_MULTICAST_FRAME_IDX_FRAME);

			//TRACE("<<MC FRAME %.16llx/%s from %s@%s flags %.2x length %u",nwid,to.toString().c_str(),from.toString().c_str(),peer->address().toString().c_str(),flags,frameLen);

			if ((frameLen > 0)&&(frameLen <= ZT_IF_MTU)) {
				if (!to.mac().isMulticast()) {
					TRACE("dropped MULTICAST_FRAME from %s@%s(%s) to %s: destination is unicast, must use FRAME or EXT_FRAME",from.toString().c_str(),peer->address().toString().c_str(),_remoteAddress.toString().c_str(),to.toString().c_str());
					return true;
				}
				if ((!from)||(from.isMulticast())||(from == network->mac())) {
					TRACE("dropped MULTICAST_FRAME from %s@%s(%s) to %s: invalid source MAC",from.toString().c_str(),peer->address().toString().c_str(),_remoteAddress.toString().c_str(),to.toString().c_str());
					return true;
				}

				if (from != MAC(peer->address(),network->id())) {
					if (network->config().permitsBridging(peer->address())) {
						network->learnBridgeRoute(from,peer->address());
					} else {
						TRACE("dropped MULTICAST_FRAME from %s@%s(%s) to %s: sender not allowed to bridge into %.16llx",from.toString().c_str(),peer->address().toString().c_str(),_remoteAddress.toString().c_str(),to.toString().c_str(),network->id());
						return true;
					}
				}

				const uint8_t *const frameData = (const uint8_t *)field(offset + ZT_PROTO_VERB_MULTICAST_FRAME_IDX_FRAME,frameLen);
				if (network->filterIncomingPacket(peer,RR->identity.address(),from,to.mac(),frameData,frameLen,etherType,0)) {
					RR->node->putFrame(network->id(),network->userPtr(),from,to.mac(),etherType,0,(const void *)frameData,frameLen);
				}
			}

			if (gatherLimit) {
				Packet outp(source(),RR->identity.address(),Packet::VERB_OK);
				outp.append((unsigned char)Packet::VERB_MULTICAST_FRAME);
				outp.append(packetId());
				outp.append(nwid);
				to.mac().appendTo(outp);
				outp.append((uint32_t)to.adi());
				outp.append((unsigned char)0x02); // flag 0x02 = contains gather results
				if (RR->mc->gather(peer->address(),nwid,to,outp,gatherLimit)) {
					outp.armor(peer->key(),true);
					RR->node->putPacket(_localAddress,_remoteAddress,outp.data(),outp.size());
				}
			}
		} // else ignore -- not a member of this network

		peer->received(_localAddress,_remoteAddress,hops(),packetId(),Packet::VERB_MULTICAST_FRAME,0,Packet::VERB_NOP);
	} catch ( ... ) {
		TRACE("dropped MULTICAST_FRAME from %s(%s): unexpected exception",source().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

bool IncomingPacket::_doPUSH_DIRECT_PATHS(const RuntimeEnvironment *RR,const SharedPtr<Peer> &peer)
{
	try {
		const uint64_t now = RR->node->now();

		// First, subject this to a rate limit
		if (!peer->shouldRespondToDirectPathPush(now)) {
			TRACE("dropped PUSH_DIRECT_PATHS from %s(%s): circuit breaker tripped",source().toString().c_str(),_remoteAddress.toString().c_str());
			return true;
		}

		// Second, limit addresses by scope and type
		uint8_t countPerScope[ZT_INETADDRESS_MAX_SCOPE+1][2]; // [][0] is v4, [][1] is v6
		memset(countPerScope,0,sizeof(countPerScope));

		unsigned int count = at<uint16_t>(ZT_PACKET_IDX_PAYLOAD);
		unsigned int ptr = ZT_PACKET_IDX_PAYLOAD + 2;

		while (count--) { // if ptr overflows Buffer will throw
			// TODO: some flags are not yet implemented

			unsigned int flags = (*this)[ptr++];
			unsigned int extLen = at<uint16_t>(ptr); ptr += 2;
			ptr += extLen; // unused right now
			unsigned int addrType = (*this)[ptr++];
			unsigned int addrLen = (*this)[ptr++];

			switch(addrType) {
				case 4: {
					InetAddress a(field(ptr,4),4,at<uint16_t>(ptr + 4));

					bool redundant = false;
					if ((flags & ZT_PUSH_DIRECT_PATHS_FLAG_CLUSTER_REDIRECT) != 0) {
						peer->setClusterOptimalPathForAddressFamily(a);
					} else {
						redundant = peer->hasActivePathTo(now,a);
					}

					if ( ((flags & ZT_PUSH_DIRECT_PATHS_FLAG_FORGET_PATH) == 0) && (!redundant) && (RR->node->shouldUsePathForZeroTierTraffic(_localAddress,a)) ) {
						if (++countPerScope[(int)a.ipScope()][0] <= ZT_PUSH_DIRECT_PATHS_MAX_PER_SCOPE_AND_FAMILY) {
							TRACE("attempting to contact %s at pushed direct path %s",peer->address().toString().c_str(),a.toString().c_str());
							peer->sendHELLO(InetAddress(),a,now);
						} else {
							TRACE("ignoring contact for %s at %s -- too many per scope",peer->address().toString().c_str(),a.toString().c_str());
						}
					}
				}	break;
				case 6: {
					InetAddress a(field(ptr,16),16,at<uint16_t>(ptr + 16));

					bool redundant = false;
					if ((flags & ZT_PUSH_DIRECT_PATHS_FLAG_CLUSTER_REDIRECT) != 0) {
						peer->setClusterOptimalPathForAddressFamily(a);
					} else {
						redundant = peer->hasActivePathTo(now,a);
					}

					if ( ((flags & ZT_PUSH_DIRECT_PATHS_FLAG_FORGET_PATH) == 0) && (!redundant) && (RR->node->shouldUsePathForZeroTierTraffic(_localAddress,a)) ) {
						if (++countPerScope[(int)a.ipScope()][1] <= ZT_PUSH_DIRECT_PATHS_MAX_PER_SCOPE_AND_FAMILY) {
							TRACE("attempting to contact %s at pushed direct path %s",peer->address().toString().c_str(),a.toString().c_str());
							peer->sendHELLO(InetAddress(),a,now);
						} else {
							TRACE("ignoring contact for %s at %s -- too many per scope",peer->address().toString().c_str(),a.toString().c_str());
						}
					}
				}	break;
			}
			ptr += addrLen;
		}

		peer->received(_localAddress,_remoteAddress,hops(),packetId(),Packet::VERB_PUSH_DIRECT_PATHS,0,Packet::VERB_NOP);
	} catch ( ... ) {
		TRACE("dropped PUSH_DIRECT_PATHS from %s(%s): unexpected exception",source().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

bool IncomingPacket::_doCIRCUIT_TEST(const RuntimeEnvironment *RR,const SharedPtr<Peer> &peer)
{
	try {
		const Address originatorAddress(field(ZT_PACKET_IDX_PAYLOAD,ZT_ADDRESS_LENGTH),ZT_ADDRESS_LENGTH);
		SharedPtr<Peer> originator(RR->topology->getPeer(originatorAddress));
		if (!originator) {
			RR->sw->requestWhois(originatorAddress);
			return false;
		}

		const unsigned int flags = at<uint16_t>(ZT_PACKET_IDX_PAYLOAD + 5);
		const uint64_t timestamp = at<uint64_t>(ZT_PACKET_IDX_PAYLOAD + 7);
		const uint64_t testId = at<uint64_t>(ZT_PACKET_IDX_PAYLOAD + 15);

		// Tracks total length of variable length fields, initialized to originator credential length below
		unsigned int vlf;

		// Originator credentials
		const unsigned int originatorCredentialLength = vlf = at<uint16_t>(ZT_PACKET_IDX_PAYLOAD + 23);
		uint64_t originatorCredentialNetworkId = 0;
		if (originatorCredentialLength >= 1) {
			switch((*this)[ZT_PACKET_IDX_PAYLOAD + 25]) {
				case 0x01: { // 64-bit network ID, originator must be controller
					if (originatorCredentialLength >= 9)
						originatorCredentialNetworkId = at<uint64_t>(ZT_PACKET_IDX_PAYLOAD + 26);
				}	break;
				default: break;
			}
		}

		// Add length of "additional fields," which are currently unused
		vlf += at<uint16_t>(ZT_PACKET_IDX_PAYLOAD + 25 + vlf);

		// Verify signature -- only tests signed by their originators are allowed
		const unsigned int signatureLength = at<uint16_t>(ZT_PACKET_IDX_PAYLOAD + 27 + vlf);
		if (!originator->identity().verify(field(ZT_PACKET_IDX_PAYLOAD,27 + vlf),27 + vlf,field(ZT_PACKET_IDX_PAYLOAD + 29 + vlf,signatureLength),signatureLength)) {
			TRACE("dropped CIRCUIT_TEST from %s(%s): signature by originator %s invalid",source().toString().c_str(),_remoteAddress.toString().c_str(),originatorAddress.toString().c_str());
			return true;
		}
		vlf += signatureLength;

		// Save this length so we can copy the immutable parts of this test
		// into the one we send along to next hops.
		const unsigned int lengthOfSignedPortionAndSignature = 29 + vlf;

		// Add length of second "additional fields" section.
		vlf += at<uint16_t>(ZT_PACKET_IDX_PAYLOAD + 29 + vlf);

		// Check credentials (signature already verified)
		NetworkConfig originatorCredentialNetworkConfig;
		if (originatorCredentialNetworkId) {
			if (Network::controllerFor(originatorCredentialNetworkId) == originatorAddress) {
				if (!RR->node->network(originatorCredentialNetworkId)) {
					TRACE("dropped CIRCUIT_TEST from %s(%s): originator %s specified network ID %.16llx as credential, and we are not a member of that network",source().toString().c_str(),_remoteAddress.toString().c_str(),originatorAddress.toString().c_str(),originatorCredentialNetworkId);
					return true;
				}
			} else {
				TRACE("dropped CIRCUIT_TEST from %s(%s): originator %s specified network ID as credential, is not controller for %.16llx",source().toString().c_str(),_remoteAddress.toString().c_str(),originatorAddress.toString().c_str(),originatorCredentialNetworkId);
				return true;
			}
		} else {
			TRACE("dropped CIRCUIT_TEST from %s(%s): originator %s did not specify a credential or credential type",source().toString().c_str(),_remoteAddress.toString().c_str(),originatorAddress.toString().c_str());
			return true;
		}

		const uint64_t now = RR->node->now();

		unsigned int breadth = 0;
		Address nextHop[256]; // breadth is a uin8_t, so this is the max
		InetAddress nextHopBestPathAddress[256];
		unsigned int remainingHopsPtr = ZT_PACKET_IDX_PAYLOAD + 33 + vlf;
		if ((ZT_PACKET_IDX_PAYLOAD + 31 + vlf) < size()) {
			// unsigned int nextHopFlags = (*this)[ZT_PACKET_IDX_PAYLOAD + 31 + vlf]
			breadth = (*this)[ZT_PACKET_IDX_PAYLOAD + 32 + vlf];
			for(unsigned int h=0;h<breadth;++h) {
				nextHop[h].setTo(field(remainingHopsPtr,ZT_ADDRESS_LENGTH),ZT_ADDRESS_LENGTH);
				remainingHopsPtr += ZT_ADDRESS_LENGTH;
				SharedPtr<Peer> nhp(RR->topology->getPeer(nextHop[h]));
				if (nhp) {
					Path *const rp = nhp->getBestPath(now);
					if (rp)
						nextHopBestPathAddress[h] = rp->address();
				}
			}
		}

		// Report back to originator, depending on flags and whether we are last hop
		if ( ((flags & 0x01) != 0) || ((breadth == 0)&&((flags & 0x02) != 0)) ) {
			Packet outp(originatorAddress,RR->identity.address(),Packet::VERB_CIRCUIT_TEST_REPORT);
			outp.append((uint64_t)timestamp);
			outp.append((uint64_t)testId);
			outp.append((uint64_t)0); // field reserved for future use
			outp.append((uint8_t)ZT_VENDOR_ZEROTIER);
			outp.append((uint8_t)ZT_PROTO_VERSION);
			outp.append((uint8_t)ZEROTIER_ONE_VERSION_MAJOR);
			outp.append((uint8_t)ZEROTIER_ONE_VERSION_MINOR);
			outp.append((uint16_t)ZEROTIER_ONE_VERSION_REVISION);
			outp.append((uint16_t)ZT_PLATFORM_UNSPECIFIED);
			outp.append((uint16_t)ZT_ARCHITECTURE_UNSPECIFIED);
			outp.append((uint16_t)0); // error code, currently unused
			outp.append((uint64_t)0); // flags, currently unused
			outp.append((uint64_t)packetId());
			peer->address().appendTo(outp);
			outp.append((uint8_t)hops());
			_localAddress.serialize(outp);
			_remoteAddress.serialize(outp);
			outp.append((uint16_t)0); // no additional fields
			outp.append((uint8_t)breadth);
			for(unsigned int h=0;h<breadth;++h) {
				nextHop[h].appendTo(outp);
				nextHopBestPathAddress[h].serialize(outp); // appends 0 if null InetAddress
			}
			RR->sw->send(outp,true);
		}

		// If there are next hops, forward the test along through the graph
		if (breadth > 0) {
			Packet outp(Address(),RR->identity.address(),Packet::VERB_CIRCUIT_TEST);
			outp.append(field(ZT_PACKET_IDX_PAYLOAD,lengthOfSignedPortionAndSignature),lengthOfSignedPortionAndSignature);
			outp.append((uint16_t)0); // no additional fields
			if (remainingHopsPtr < size())
				outp.append(field(remainingHopsPtr,size() - remainingHopsPtr),size() - remainingHopsPtr);

			for(unsigned int h=0;h<breadth;++h) {
				if (RR->identity.address() != nextHop[h]) { // next hops that loop back to the current hop are not valid
					outp.newInitializationVector();
					outp.setDestination(nextHop[h]);
					RR->sw->send(outp,true);
				}
			}
		}

		peer->received(_localAddress,_remoteAddress,hops(),packetId(),Packet::VERB_CIRCUIT_TEST,0,Packet::VERB_NOP);
	} catch ( ... ) {
		TRACE("dropped CIRCUIT_TEST from %s(%s): unexpected exception",source().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

bool IncomingPacket::_doCIRCUIT_TEST_REPORT(const RuntimeEnvironment *RR,const SharedPtr<Peer> &peer)
{
	try {
		ZT_CircuitTestReport report;
		memset(&report,0,sizeof(report));

		report.current = peer->address().toInt();
		report.upstream = Address(field(ZT_PACKET_IDX_PAYLOAD + 52,ZT_ADDRESS_LENGTH),ZT_ADDRESS_LENGTH).toInt();
		report.testId = at<uint64_t>(ZT_PACKET_IDX_PAYLOAD + 8);
		report.timestamp = at<uint64_t>(ZT_PACKET_IDX_PAYLOAD);
		report.remoteTimestamp = at<uint64_t>(ZT_PACKET_IDX_PAYLOAD + 16);
		report.sourcePacketId = at<uint64_t>(ZT_PACKET_IDX_PAYLOAD + 44);
		report.flags = at<uint64_t>(ZT_PACKET_IDX_PAYLOAD + 36);
		report.sourcePacketHopCount = (*this)[ZT_PACKET_IDX_PAYLOAD + 57]; // end of fixed length headers: 58
		report.errorCode = at<uint16_t>(ZT_PACKET_IDX_PAYLOAD + 34);
		report.vendor = (enum ZT_Vendor)((*this)[ZT_PACKET_IDX_PAYLOAD + 24]);
		report.protocolVersion = (*this)[ZT_PACKET_IDX_PAYLOAD + 25];
		report.majorVersion = (*this)[ZT_PACKET_IDX_PAYLOAD + 26];
		report.minorVersion = (*this)[ZT_PACKET_IDX_PAYLOAD + 27];
		report.revision = at<uint16_t>(ZT_PACKET_IDX_PAYLOAD + 28);
		report.platform = (enum ZT_Platform)at<uint16_t>(ZT_PACKET_IDX_PAYLOAD + 30);
		report.architecture = (enum ZT_Architecture)at<uint16_t>(ZT_PACKET_IDX_PAYLOAD + 32);

		const unsigned int receivedOnLocalAddressLen = reinterpret_cast<InetAddress *>(&(report.receivedOnLocalAddress))->deserialize(*this,ZT_PACKET_IDX_PAYLOAD + 58);
		const unsigned int receivedFromRemoteAddressLen = reinterpret_cast<InetAddress *>(&(report.receivedFromRemoteAddress))->deserialize(*this,ZT_PACKET_IDX_PAYLOAD + 58 + receivedOnLocalAddressLen);

		unsigned int nhptr = ZT_PACKET_IDX_PAYLOAD + 58 + receivedOnLocalAddressLen + receivedFromRemoteAddressLen;
		nhptr += at<uint16_t>(nhptr) + 2; // add "additional field" length, which right now will be zero

		report.nextHopCount = (*this)[nhptr++];
		if (report.nextHopCount > ZT_CIRCUIT_TEST_MAX_HOP_BREADTH) // sanity check, shouldn't be possible
			report.nextHopCount = ZT_CIRCUIT_TEST_MAX_HOP_BREADTH;
		for(unsigned int h=0;h<report.nextHopCount;++h) {
			report.nextHops[h].address = Address(field(nhptr,ZT_ADDRESS_LENGTH),ZT_ADDRESS_LENGTH).toInt(); nhptr += ZT_ADDRESS_LENGTH;
			nhptr += reinterpret_cast<InetAddress *>(&(report.nextHops[h].physicalAddress))->deserialize(*this,nhptr);
		}

		RR->node->postCircuitTestReport(&report);
	} catch ( ... ) {
		TRACE("dropped CIRCUIT_TEST_REPORT from %s(%s): unexpected exception",source().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

bool IncomingPacket::_doREQUEST_PROOF_OF_WORK(const RuntimeEnvironment *RR,const SharedPtr<Peer> &peer)
{
	try {
		// If this were allowed from anyone, it would itself be a DOS vector. Right
		// now we only allow it from roots and controllers of networks you have joined.
		bool allowed = RR->topology->isUpstream(peer->identity());
		if (!allowed) {
			std::vector< SharedPtr<Network> > allNetworks(RR->node->allNetworks());
			for(std::vector< SharedPtr<Network> >::const_iterator n(allNetworks.begin());n!=allNetworks.end();++n) {
				if (peer->address() == (*n)->controller()) {
					allowed = true;
					break;
				}
			}
		}

		if (allowed) {
			const uint64_t pid = packetId();
			const unsigned int difficulty = (*this)[ZT_PACKET_IDX_PAYLOAD + 1];
			const unsigned int challengeLength = at<uint16_t>(ZT_PACKET_IDX_PAYLOAD + 2);
			if (challengeLength > ZT_PROTO_MAX_PACKET_LENGTH)
				return true; // sanity check, drop invalid size
			const unsigned char *challenge = field(ZT_PACKET_IDX_PAYLOAD + 4,challengeLength);

			switch((*this)[ZT_PACKET_IDX_PAYLOAD]) {

				// Salsa20/12+SHA512 hashcash
				case 0x01: {
					if (difficulty <= 14) {
						unsigned char result[16];
						computeSalsa2012Sha512ProofOfWork(difficulty,challenge,challengeLength,result);
						TRACE("PROOF_OF_WORK computed for %s: difficulty==%u, challengeLength==%u, result: %.16llx%.16llx",peer->address().toString().c_str(),difficulty,challengeLength,Utils::ntoh(*(reinterpret_cast<const uint64_t *>(result))),Utils::ntoh(*(reinterpret_cast<const uint64_t *>(result + 8))));
						Packet outp(peer->address(),RR->identity.address(),Packet::VERB_OK);
						outp.append((unsigned char)Packet::VERB_REQUEST_PROOF_OF_WORK);
						outp.append(pid);
						outp.append((uint16_t)sizeof(result));
						outp.append(result,sizeof(result));
						outp.armor(peer->key(),true);
						RR->node->putPacket(_localAddress,_remoteAddress,outp.data(),outp.size());
					} else {
						Packet outp(peer->address(),RR->identity.address(),Packet::VERB_ERROR);
						outp.append((unsigned char)Packet::VERB_REQUEST_PROOF_OF_WORK);
						outp.append(pid);
						outp.append((unsigned char)Packet::ERROR_INVALID_REQUEST);
						outp.armor(peer->key(),true);
						RR->node->putPacket(_localAddress,_remoteAddress,outp.data(),outp.size());
					}
				}	break;

				default:
					TRACE("dropped REQUEST_PROOF_OF_WORK from %s(%s): unrecognized proof of work type",peer->address().toString().c_str(),_remoteAddress.toString().c_str());
					break;
			}

			peer->received(_localAddress,_remoteAddress,hops(),pid,Packet::VERB_REQUEST_PROOF_OF_WORK,0,Packet::VERB_NOP);
		} else {
			TRACE("dropped REQUEST_PROOF_OF_WORK from %s(%s): not trusted enough",peer->address().toString().c_str(),_remoteAddress.toString().c_str());
		}
	} catch ( ... ) {
		TRACE("dropped REQUEST_PROOF_OF_WORK from %s(%s): unexpected exception",peer->address().toString().c_str(),_remoteAddress.toString().c_str());
	}
	return true;
}

void IncomingPacket::computeSalsa2012Sha512ProofOfWork(unsigned int difficulty,const void *challenge,unsigned int challengeLength,unsigned char result[16])
{
	unsigned char salsabuf[131072]; // 131072 == protocol constant, size of memory buffer for this proof of work function
	char candidatebuf[ZT_PROTO_MAX_PACKET_LENGTH + 256];
	unsigned char shabuf[ZT_SHA512_DIGEST_LEN];
	const uint64_t s20iv = 0; // zero IV for Salsa20
	char *const candidate = (char *)(( ((uintptr_t)&(candidatebuf[0])) | 0xf ) + 1); // align to 16-byte boundary to ensure that uint64_t type punning of initial nonce is okay
	Salsa20 s20;
	unsigned int d;
	unsigned char *p;

	Utils::getSecureRandom(candidate,16);
	memcpy(candidate + 16,challenge,challengeLength);

	if (difficulty > 512)
		difficulty = 512; // sanity check

try_salsa2012sha512_again:
	++*(reinterpret_cast<volatile uint64_t *>(candidate));

	SHA512::hash(shabuf,candidate,16 + challengeLength);
	s20.init(shabuf,256,&s20iv);
	memset(salsabuf,0,sizeof(salsabuf));
	s20.encrypt12(salsabuf,salsabuf,sizeof(salsabuf));
	SHA512::hash(shabuf,salsabuf,sizeof(salsabuf));

	d = difficulty;
	p = shabuf;
	while (d >= 8) {
		if (*(p++))
			goto try_salsa2012sha512_again;
		d -= 8;
	}
	if (d > 0) {
		if ( ((((unsigned int)*p) << d) & 0xff00) != 0 )
			goto try_salsa2012sha512_again;
	}

	memcpy(result,candidate,16);
}

bool IncomingPacket::testSalsa2012Sha512ProofOfWorkResult(unsigned int difficulty,const void *challenge,unsigned int challengeLength,const unsigned char proposedResult[16])
{
	unsigned char salsabuf[131072]; // 131072 == protocol constant, size of memory buffer for this proof of work function
	char candidate[ZT_PROTO_MAX_PACKET_LENGTH + 256];
	unsigned char shabuf[ZT_SHA512_DIGEST_LEN];
	const uint64_t s20iv = 0; // zero IV for Salsa20
	Salsa20 s20;
	unsigned int d;
	unsigned char *p;

	if (difficulty > 512)
		difficulty = 512; // sanity check

	memcpy(candidate,proposedResult,16);
	memcpy(candidate + 16,challenge,challengeLength);

	SHA512::hash(shabuf,candidate,16 + challengeLength);
	s20.init(shabuf,256,&s20iv);
	memset(salsabuf,0,sizeof(salsabuf));
	s20.encrypt12(salsabuf,salsabuf,sizeof(salsabuf));
	SHA512::hash(shabuf,salsabuf,sizeof(salsabuf));

	d = difficulty;
	p = shabuf;
	while (d >= 8) {
		if (*(p++))
			return false;
		d -= 8;
	}
	if (d > 0) {
		if ( ((((unsigned int)*p) << d) & 0xff00) != 0 )
			return false;
	}

	return true;
}

} // namespace ZeroTier