Layer 2 Multicast Addresses; Ip Multicast Delivery Modes - Cisco Catalyst 3850 series Configuration Manual

IP Multicast Routing Technology Overview
mechanism in one-to-many communications. SSM is described in the
27 section.
GLOP Addresses
GLOP addressing (as proposed by RFC 2770, GLOP Addressing in 233/8) proposes that the 233.0.0.0/8 range
be reserved for statically defined addresses by organizations that already have an AS number reserved. This
practice is called GLOP addressing. The AS number of the domain is embedded into the second and third
octets of the 233.0.0.0/8 address range. For example, AS 62010 is written in hexadecimal format as F23A.
Separating the two octets F2 and 3A results in 242 and 58 in decimal format. These values result in a subnet
of 233.242.58.0/24 that would be globally reserved for AS 62010 to use.
Limited Scope Addresses
The range 239.0.0.0 to 239.255.255.255 is reserved as administratively or limited scoped addresses for use
in private multicast domains. These addresses are constrained to a local group or organization. Companies,
universities, and other organizations can use limited scope addresses to have local multicast applications that
will not be forwarded outside their domain. Routers typically are configured with filters to prevent multicast
traffic in this address range from flowing outside an autonomous system (AS) or any user-defined domain.
Within an AS or domain, the limited scope address range can be further subdivided so that local multicast
boundaries can be defined.
Note Network administrators may use multicast addresses in this range, inside a domain, without conflicting
with others elsewhere in the Internet.

Layer 2 Multicast Addresses

Historically, network interface cards (NICs) on a LAN segment could receive only packets destined for their
burned-in MAC address or the broadcast MAC address. In IP multicast, several hosts need to be able to receive
a single data stream with a common destination MAC address. Some means had to be devised so that multiple
hosts could receive the same packet and still be able to differentiate between several multicast groups. One
method to accomplish this is to map IP multicast Class D addresses directly to a MAC address. Using this
method, NICs can receive packets destined to many different MAC address.
Cisco Group Management Protocol ( CGMP) is used on routers connected to Catalyst switches to perform
tasks similar to those performed by IGMP. CGMP is necessary for those Catalyst switches that cannot
distinguish between IP multicast data packets and IGMP report messages, both of which are addressed to the
same group address at the MAC level.

IP Multicast Delivery Modes

IP multicast delivery modes differ only for the receiver hosts, not for the source hosts. A source host sends
IP multicast packets with its own IP address as the IP source address of the packet and a group address as the
IP destination address of the packet.
OL-32598-01
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3.6E (Catalyst 3850 Switches)
Layer 2 Multicast Addresses
IP Multicast Delivery Modes, on page
27