ZeroTierOne/node/MulticastGroup.hpp

/*
 * 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.
 */
/****/

#ifndef ZT_MULTICASTGROUP_HPP
#define ZT_MULTICASTGROUP_HPP

#include "InetAddress.hpp"
#include "MAC.hpp"

#include <stdint.h>

namespace ZeroTier {

/**
 * A multicast group composed of a multicast MAC and a 32-bit ADI field
 *
 * ADI stands for additional distinguishing information. ADI is primarily for
 * adding additional information to broadcast (ff:ff:ff:ff:ff:ff) memberships,
 * since straight-up broadcast won't scale. Right now it's zero except for
 * IPv4 ARP, where it holds the IPv4 address itself to make ARP into a
 * selective multicast query that can scale.
 *
 * In the future we might add some kind of plugin architecture that can add
 * ADI for things like mDNS (multicast DNS) to improve the selectivity of
 * those protocols.
 *
 * MulticastGroup behaves as an immutable value object.
 */
class MulticastGroup {
  public:
	MulticastGroup() : _mac(), _adi(0)
	{
	}

	MulticastGroup(const MAC& m, uint32_t a) : _mac(m), _adi(a)
	{
	}

	/**
	 * Derive the multicast group used for address resolution (ARP/NDP) for an IP
	 *
	 * @param ip IP address (port field is ignored)
	 * @return Multicast group for ARP/NDP
	 */
	static inline MulticastGroup deriveMulticastGroupForAddressResolution(const InetAddress& ip)
	{
		if (ip.isV4()) {
			// IPv4 wants broadcast MACs, so we shove the V4 address itself into
			// the Multicast Group ADI field. Making V4 ARP work is basically why
			// ADI was added, as well as handling other things that want mindless
			// Ethernet broadcast to all.
			return MulticastGroup(MAC(0xffffffffffffULL), Utils::ntoh(*((const uint32_t*)ip.rawIpData())));
		}
		else if (ip.isV6()) {
			// IPv6 is better designed in this respect. We can compute the IPv6
			// multicast address directly from the IP address, and it gives us
			// 24 bits of uniqueness. Collisions aren't likely to be common enough
			// to care about.
			const unsigned char* a = (const unsigned char*)ip.rawIpData();
			return MulticastGroup(MAC(0x33, 0x33, 0xff, a[13], a[14], a[15]), 0);
		}
		return MulticastGroup();
	}

	/**
	 * @return Multicast address
	 */
	inline const MAC& mac() const
	{
		return _mac;
	}

	/**
	 * @return Additional distinguishing information
	 */
	inline uint32_t adi() const
	{
		return _adi;
	}

	inline unsigned long hashCode() const
	{
		return (_mac.hashCode() ^ (unsigned long)_adi);
	}

	inline bool operator==(const MulticastGroup& g) const
	{
		return ((_mac == g._mac) && (_adi == g._adi));
	}
	inline bool operator!=(const MulticastGroup& g) const
	{
		return ((_mac != g._mac) || (_adi != g._adi));
	}
	inline bool operator<(const MulticastGroup& g) const
	{
		if (_mac < g._mac) {
			return true;
		}
		else if (_mac == g._mac) {
			return (_adi < g._adi);
		}
		return false;
	}
	inline bool operator>(const MulticastGroup& g) const
	{
		return (g < *this);
	}
	inline bool operator<=(const MulticastGroup& g) const
	{
		return ! (g < *this);
	}
	inline bool operator>=(const MulticastGroup& g) const
	{
		return ! (*this < g);
	}

  private:
	MAC _mac;
	uint32_t _adi;
};

}	// namespace ZeroTier

#endif