Dell Force10 Z9000 FTOS Configuration Guide for Z9000 System - Page 363

Sending an Unsolicited IGMP Report A host does not have to wait for a general query to join a group. It may send an unsolicited IGMP Membership Report, also called an IGMP Join message, to the querier. Leaving a Multicast Group 1. A host sends a membership report of type 0x17 (IGMP Leave message) to the all routers multicast address 224.0.0.2 when it no longer cares about multicast traffic for a particular group. 2. The querier sends a Group-Specific Query to determine whether there are any remaining hosts in the group. There must be at least one receiver in a group on a subnet for a router to forward multicast traffic for that group to the subnet. 3. Any remaining hosts respond to the query according to the delay timer mechanism (see Adjusting Query and Response Timers on page 368). If no hosts respond (because there are none remaining in the group) the querier waits a specified period, and sends another query. If it still receives no response, the querier removes the group from the list associated with forwarding port and stops forwarding traffic for that group to the subnet. IGMP version 3 Conceptually, IGMP version 3 behaves the same as version 2. There are differences: • Version 3 adds the ability to filter by multicast source, which helps multicast routing protocols avoid forwarding traffic to subnets where there are no interested receivers. • To enable filtering, routers must keep track of more state information, that is, the list of sources that must be filtered. An additional query type, the Group-and-Source-Specific Query, keeps track of state changes, while the Group-Specific and General queries still refresh existing state. • Reporting is more efficient and robust: hosts do not suppress query responses (non-suppression helps track state and enables the immediate-leave and IGMP Snooping features), state-change reports are retransmitted to insure delivery, and a single membership report bundles multiple statements from a single host, rather than sending an individual packet for each statement. The version 3 packet structure is different from version 2 to accommodate these protocol enhancements. Queries (Figure 18-2) are still sent to the all-systems address 224.0.0.1, but reports (Figure 18-3) are sent to the all IGMP version 3-capable multicast routers address 244.0.0.22. Figure 18-2. IGMP version 3 Membership Query Packet Format Type (0x11) Max. Response Code Checksum Group Address Reserved S Querier Robustness Querier's Query Number of Value Interval Code Sources (2) Source Addresses Maximum Response Time derived from this value Code: 0x11: Membership Query Bit flag that when set to 1 suppresses router query response timer updates Query Interval derived from this value Source addresses to be filtered Number of times that a router or receiver transmits a query or report to insure that it is received Number of source addresses to be filtered fnC0070mp Internet Group Management Protocol (IGMP) | 363