Ethernet frames with a value of 1 in the least-significant bit of the first octet[note 2] of the destination address are treated as multicast frames and are flooded to all points on the network. While frames with ones in all bits of the destination address (FF:FF:FF:FF:FF:FF) are sometimes referred to as broadcasts, Ethernet network equipment generally does not distinguish between multicast and broadcast frames. Modern Ethernet controllers filter received packets to reduce CPU load, by looking up the hash of a multicast destination address in a table, initialized by software, which controls whether a multicast packet is dropped or fully received.
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Some well known Ethernet multicast addresses
Ethernet multicast address Type Field Usage 01:00:0C:CC:CC:CC 0x0802 CDP |(Cisco Discovery Protocol), VTP (VLAN Trunking Protocol) 01:00:0C:CC:CC:CD 0x0802 Cisco Shared Spanning Tree Protocol Address 01:80:C2:00:00:00 0x0802 Spanning Tree Protocol (for bridges) IEEE 802.1D 01:80:C2:00:00:00, or 01:80:C2:00:00:03, or 01:80:C2:00:00:0E 0x88CC Link Layer Discovery Protocol 01:80:C2:00:00:08 0x0802 Spanning Tree Protocol (for provider bridges) IEEE 802.1ad 01:80:C2:00:00:01 0x8808 Ethernet flow control (Pause frame) IEEE 802.3x 01:80:C2:00:00:02 0x8809 Ethernet OAM Protocol IEEE 802.3ah (A.K.A. “slow protocols”) 01:80:C2:00:00:30 to 01:80:C2:00:00:3F 0x8902 Ethernet CFM Protocol IEEE 802.1ag 01:00:5E:00:00:00 – 01:00:5E:7F:FF:FF 0x0800 IPv4 Multicast (RFC 1112), insert the low 23 Bits of the multicast IPv4 Address into the Ethernet Address (RFC 7042 2.1.1.) 33:33:xx:xx:xx:xx 0x86DD IPv6 Multicast (RFC 2464), insert the low 32 Bits of the multicast IPv6 Address into the Ethernet Address (RFC 7042 2.3.1.) 01:1B:19:00:00:00, or 01:80:C2:00:00:0E 0x88F7 Precision Time Protocol (PTP) version 2 over Ethernet (Layer-2)
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