Leave reports
Another announcement mechanism that is commonly seen with many multicast applications is the " Leave Report,” used to announce that a particular host is no longer interested in receiving multicast traffic for a particular group. The idea behind this report is that it can be used to inform a local multicast router that the host is going away, and that the router can stop forwarding multicast data for the specified group address to this network.
There are some special considerations with this type of report. For one thing, the router has to verify that the host that is leaving the multicast group is indeed the last user of the specified group address, otherwise any other hosts on the local network that still wanted to receive traffic for that group wouldn’t get it any more. This is achieved through the use of a group-specific query message (as we’ll discuss next in Section 4.1.4.3). If no hosts respond to the group-specific query, the router can stop forwarding traffic for that group’s multicast address immediately, thereby reducing the local bandwidth consumption.
Furthermore, Leave Reports were introduced in the IGMPv2 specification, and were not a part of the IGMPv1 specification. As such, they will only be used on systems that use IGMPv2, and will be ignored by systems that are using IGMPv1.
It is important to note that Leave Reports are not sent to the multicast address of the group being left as are Membership Reports, but instead are sent to the “all-routers” group ...
Get Internet Core Protocols: The Definitive Guide now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.
