Information About Igmp; Ip Multicast Group Addresses - Cisco Catalyst 3650 Configuration Manual

Information About IGMP

• IGMP Version 3 uses new membership report messages that might not be correctly recognized by older
• IGMP filtering and throttling is not supported under the WLAN.
• You cannot have a device stack containing a mix of Catalyst 3850 and Catalyst 3650 devices.

Information About IGMP

Internet Group Management Protocol (IGMP) is used to dynamically register individual hosts in a multicast
group on a particular LAN. Enabling PIM on an interface also enables IGMP. IGMP provides a means to
automatically control and limit the flow of multicast traffic throughout your network with the use of special
multicast queriers and hosts.
To participate in IP multicasting, multicast hosts, routers, and multilayer devices must have the Internet Group
Management Protocol (IGMP) operating. This protocol defines the querier and host roles:
• A querier is a network device that sends query messages to discover which network devices are members
• A host is a receiver that sends report messages (in response to query messages) to inform a querier of a
Hosts identify group memberships by sending IGMP messages to their local multicast device. Under IGMP,
devices listen to IGMP messages and periodically send out queries to discover which groups are active or
inactive on a particular subnet.
A set of queriers and hosts that receive multicast data streams from the same source is called a multicast group.
Queriers and hosts use IGMP messages to join and leave multicast groups.
Any host, regardless of whether it is a member of a group, can send to a group. However, only the members
of a group receive the message. Membership in a multicast group is dynamic; hosts can join and leave at any
time. There is no restriction on the location or number of members in a multicast group. A host can be a
member of more than one multicast group at a time. How active a multicast group is and what members it has
can vary from group to group and from time to time. A multicast group can be active for a long time, or it can
be very short-lived. Membership in a group can constantly change.

IP Multicast Group Addresses

IP multicast traffic uses group addresses, which are class D addresses. The high-order bits of a Class D address
are 1110. Therefore, host group addresses can be in the range 224.0.0.0 through 239.255.255.255. Multicast
addresses in the range 224.0.0.0 to 224.0.0.255 are reserved for use by routing protocols and other network
control traffic. The address 224.0.0.0 is guaranteed not to be assigned to any group.
IGMP packets are sent using these IP multicast group addresses:
• IGMP general queries are destined to the address 224.0.0.1 (all systems on a subnet).
• IGMP group-specific queries are destined to the group IP address for which the device is querying.
• IGMP group membership reports are destined to the group IP address for which the device is reporting.
IP Multicast Routing Configuration Guide, Cisco IOS XE Release 3SE (Catalyst 3650 Switches)
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IGMP snooping devices.
of a given multicast group.
host membership.
Configuring IGMP
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