Filter
Top Products
DES-7200 Configuration Guide Chapter 4 MLD
Configuration
4-1
4 MLD Configuration
4.1 MLD Overview
IPv6 multicast is a network technology allowing one or more senders (multicast
sources) to send a single packet to multiple receivers (once and simultaneous).
The multicast source sends the packet to a specific multicast group, and only
hosts having addresses of this multicast group can receive the packet.
Multicasting can substantially save network bandwidth, because only one packet
is sent on any link of the entire network no matter how many destination
addresses exist.
The format of IPv6 multicast address is different from that of IPv6 unicast address,
and can only be used for destination address. The first byte of address format all
consists of "1" (multicast address). The multicast address occupies 1/256 of the
IPv6 address space. Except for parts other than the first byte, the multicast
address format includes the following fields:
Flag field: (starting from high-order bit) The first bit is the reserved bit set to 0; the
second bit is R flag: R = 1 indicates a multicast address that embeds the address
of the RP, while R = 0 indicates a multicast address that does not embed the
address of the RP; the third bit is P bit: R = 1 indicates a multicast address is
created on basis of unicast prefix, otherwise it is set to 0.
The scop field has 4 bits and indicates the scope of multicasting. According to the
definition given in RFC 4291: 1 (hexadecimal number system) indicates
interface-local scope, 2 indicates link-local scope, 4 indicates admin-local scope,
5 indicates site-local scope, 8 indicates organization-local scope, and E indicates
global scope.
Group ID has 112 bits, and is used to identify the multicast group. According to
the multicast address (transient or well-known) and the scope of address, the
same multicast ID can indicate different groups. Well-known multicast address
uses specific group ID with special meanings.
No matter whether a member of multicast group or not, any host can be a
multicast source. However, only the member of multicast group can receive the
multicast frames. Members of the multicast group are determined dynamically,
and the host can dynamically join or leave the group. The multicast frames are
forwarded by the multicast device, which will run the multicast routing protocol.
To participate in IPv6 multicast, the multicast host/device shall be able to support
MLD operations. This protocol allows the interactive multicasting of member
relationship between host and routing device, so as to decide on the forwarding of
multicast steam. By utilizing the information obtained from MLD, the device will
maintain a multicast listener state table, which is based on each interface. When
the local link of an interface has at least one host being a member of the group,