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NE20E-S V800R010C10SPC500 Feature Description - IP Multicast 01

This is NE20E-S V800R010C10SPC500 Feature Description - IP Multicast

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Multicast Addresses

Multicast Addresses

The multicast addressing mechanism determines the destination of a packet and how to determine a destination address.

Multicast addressing has the following needs:

  • Multicast IP addresses are needed to implement the communication between a source and its receivers on the network layer.

  • Link layer multicast (also known as hardware multicast) is needed to transmit multicast data on a local physical network. On an Ethernet link layer network, hardware multicast uses multicast MAC addresses.

  • An IP-to-MAC address mapping technology is needed to map multicast IP addresses to multicast MAC addresses.

IPv4 Multicast Addresses

IPv4 addresses are classified as Class A, B, C, D, or E. Class D addresses are IPv4 multicast addresses and are carried in packets' destination address fields to identify multicast groups.

A multicast packet's source address field is a Class A, B, or C unicast address. A Class D address cannot be a source IP address in a multicast packet. Class E addresses are reserved for future use.

All receivers of a multicast group are identified by the same IPv4 multicast group address on the network layer. Once a user joins the group, the user can receive all IP packets sent to the group.

Class D addresses are in the 224.0.0.0 to 239.255.255.255 range. For details, see Table 2-2.

Table 2-2 Class D addresses

Class D Address Range

Description

224.0.0.0 to 224.0.0.255

Permanent multicast group addresses reserved by the Internet Assigned Number Authority (IANA) for routing protocols

224.0.1.0 to 231.255.255.255

233.0.0.0 to 238.255.255.255

Temporary any-source multicast (ASM) group addresses valid on the entire network

232.0.0.0 to 232.255.255.255

Temporary source-specific multicast (SSM) group addresses valid on the entire network

239.0.0.0 to 239.255.255.255

Temporary ASM group addresses valid only in local administration domains

A local administration multicast address is a private address and can be used in different multicast administration domains.

  • A permanent multicast group address, also known as a reserved multicast group address, identifies all devices in a multicast group that may contain any number (including 0) of members. For details, see Table 2-3.

  • A temporary multicast group address, also known as a common group address, is an IPv4 address that is assigned to a multicast group temporarily. If there is no user in this group, this address is reclaimed.

Table 2-3 General permanent multicast group addresses

Permanent Multicast Group Address

Usage

224.0.0.0

Unassigned address

224.0.0.1

Address of all hosts and routers on a network segment (this address works like a broadcast address)

224.0.0.2

Address of all multicast routers

224.0.0.3

Unassigned address

224.0.0.4

Address of Distance Vector Multicast Routing Protocol (DVMRP) devices

224.0.0.5

Address of Open Shortest Path First (OSPF) devices

224.0.0.6

Address of OSPF designated router (DR)

224.0.0.7

Address of ST devices

224.0.0.8

Address of ST hosts

224.0.0.9

Address of RIP version 2 (RIP-2) devices

224.0.0.11

Address of mobile agents

224.0.0.12

Address of Dynamic Host Configuration Protocol (DHCP) servers or relay agents

224.0.0.13

Address of all Protocol Independent Multicast (PIM) devices

224.0.0.14

Address of Resource Reservation Protocol (RSVP) devices

224.0.0.15

Address of all CBT devices

224.0.0.16

Address of a designated SBM

224.0.0.17

Address of all SBMSs

224.0.0.18

Address of Virtual Router Redundancy Protocol (VRRP) devices

224.0.0.19 to 224.0.0.21

Unassigned addresses

224.0.0.22

Address of all Internet Group Management Protocol version 3 (IGMPv3) routers

224.0.0.23 to 224.0.0.255

Unassigned addresses

IPv6 Multicast Addresses

Figure 2-3 shows the format of an IPv6 multicast address.

Figure 2-3 IPv6 multicast address format

  • An IPv6 multicast address starts with FF.

  • The flags field (4 bits) indicates the multicast type. Values in this field are defined as follows:
    • 0: well-known multicast address defined by the IANA

    • 1: multicast address of the ASM model

    • 2: multicast address of the ASM model

    • 3: multicast address of the SSM model

    • Other value: unassigned multicast address

  • The scope field (4 bits) indicates whether a multicast group contains any node in the global address space or only the nodes of the same local network, the same site, or the same organization. Values in this field are defined as follows:
    • 0: reserved for other multicast protocol usage

    • 1: node/interface-local scope

    • 2: link-local scope

    • 3: reserved for other multicast protocol usage

    • 4: admin-local scope

    • 5: site-local scope

    • 8: organization-local scope

    • E: global scope

    • F: reserved for other multicast protocol usage

    • Other value: unassigned and can be used as a common address

Table 2-4 shows the scopes and meanings of fixed IPv6 multicast addresses.

Table 2-4 IPv6 multicast addresses

Scope

Description

FF0x::/32

Well-known multicast addresses defined by the IANA

For details, see Table 2-5.

FF1x::/32 (x cannot be 1 or 2)

FF2x::/32 (x cannot be 1 or 2)

ASM addresses valid on the entire network

FF3x::/32 (x cannot be 1 or 2)

SSM addresses

This is the default SSM group address scope and is valid on the entire network.

Table 2-5 Commonly used IPv6 multicast addresses

Scope

IPv6 Multicast Address

Description

Node/interface-local scope

FF01:0:0:0:0:0:0:1

Address of all hosts and routers on a network segment (this address works like a broadcast address)

FF01:0:0:0:0:0:0:2

Address of all routers

Link-local scope

FF02:0:0:0:0:0:0:1

Address of all nodes

FF02:0:0:0:0:0:0:2

Address of all routers

FF02:0:0:0:0:0:0:3

Undefined address

FF02:0:0:0:0:0:0:4

Address of DVMRP devices

FF02:0:0:0:0:0:0:5

Address of OSPF devices

FF02:0:0:0:0:0:0:6

Address of OSPF designated routers

FF02:0:0:0:0:0:0:7

Address of ST devices

FF02:0:0:0:0:0:0:8

Address of ST hosts

FF02:0:0:0:0:0:0:9

Address of Routing Information Protocol (RIP) devices

FF02:0:0:0:0:0:0:A

Address of Enhanced Interior Gateway Routing Protocol (EIGRP) devices

FF02:0:0:0:0:0:0:B

Address of mobile agents

FF02:0:0:0:0:0:0:D

Address of all PIM devices

FF02:0:0:0:0:0:0:E

Address of RSVP devices

FF02:0:0:0:0:0:1:1

Address of links

FF02:0:0:0:0:0:1:2

Address of all DHCP agents

FF02:0:0:0:0:1:FFXX:XXXX

Solicited node address

XX:XXXX indicates the 24 least significant bits of an IPv6 address.

Site-local scope

FF05:0:0:0:0:0:0:2

Address of all routers

FF05:0:0:0:0:0:1:3

Address of all DHCP severs

FF05:0:0:0:0:0:1:4

Address of all DHCP relays

FF05:0:0:0:0:0:1:1000 to FF05:0:0:0:0:0:1:13FF

Addresses of service locations

Multicast MAC Addresses

IEEE802.3 defines unicast and multicast MAC addresses as follows:
  • The last bit in the first byte of a unicast address is fixed at 0.
  • The last bit in the first byte of a multicast address is fixed at 1.

Multicast MAC addresses identify receivers of the same multicast group at the link layer.

Ethernet interface boards can identify multicast MAC addresses. After a multicast MAC address of a multicast group is configured on a device's driver, the device can then receive and forward data of the multicast group on the Ethernet. The mapping between the multicast IPv4 address and multicast IPv4 MAC address is as follows:

As defined by the IANA, the 24 most significant bits of a MAC address are 0x01005e, the 25th bit is 0, and the 23 least significant bits are the same as those of a multicast IPv4 address. Figure 2-4 shows the mapping relationships between multicast IPv4 addresses and multicast MAC addresses.

Figure 2-4 Mapping relationships between multicast IPv4 addresses and multicast MAC addresses

The first four bits of an IPv4 multicast address, 1110, are mapped to the 25 most significant bits of a multicast MAC address. In the last 28 bits, only 23 bits are mapped to a MAC address, resulting in the loss of 5 bits. Therefore, 32 IPv4 multicast addresses are mapped to the same MAC address.

The IANA defines that the higher-order 16 bits of an IPv6 MAC address are 0x3333, and the low-order 32 bits of an IPv6 MAC address are the same as those of a multicast IPv6 address. Figure 2-5 shows the mapping relationship between the multicast IPv6 address and multicast IPv6 MAC address.
Figure 2-5 Mapping relationships between multicast IPv6 addresses and multicast MAC addresses

NOTE:

This document focuses on IP multicast technology and device operation. Multicast in the document refers to IP multicast, unless otherwise specified.

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Updated: 2019-01-03

Document ID: EDOC1100055119

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