Filter
Top Products
DES-7200 Configuration Guide Chapter 3 IGMP
Configuration
3-2
Version 1 membership report
Version 2 membership report
Leave group
IGMPv2 is basically the same as IGMPv1, except that the leave mechanism of
the host has been improved. For V2, the host can send a leave message to notify
the device, which then sends a query to verify if there is a host in the multicast
group. This makes joining and leaving a group more efficiently.
In the multicast network that runs IGMP, there is a dedicated query multicast
device, which is responsible for sending IGMP query messages. This de querier
is chosen through an election process. At the beginning, all the devices are
queriers. When a device receives a query message, it compares the source IP
address of the message. For IGMPv1, the device of the highest IP address is
elected as the querier. However, for IGMPv2/v3, the one of the lowest IP address
is selected as the querier. Moreover, for the IGMP query messages with different
versions, the one sending the IGMP query message of the lowest version is
elected as the querier.
If the querier fails, the querier is elected again. The non-querier devices maintain
the interval timers of other queriers. Every time when a device receives a
membership query packet, it resets the timer. If the timer expires, the device
considers itself is the querier and starts to send query messages. The querier
election starts again.
The querier must send the membership query request periodically to ensure that
other devices in the network know that the querier still works. For this purpose,
the querier maintains one query interval timer. When it sends the membership
query message, this timer will be reset. When the interval timer times out, the
querier sends another membership query.
When the device appears for the first time, that is, a new device is added, it sends
a series of general query messages to see which multicast groups will be
received on the hosts of which interfaces for rapid convergence. The number of
common query packets sent is based on the start query count configured. The
querying interval between the initial general query messages is defined through
the startup query interval.
When a querier receives a leave packet, it must send a particular group
membership query to see if the host is the last one leaving the group. Before the
querier stops forwarding packets to the group, it sends a series of such packets,
the number of which is equal to the last member query number. The querier
sends multiple particular membership queries to ensure that there is no member
in the group. Such a query is sent every other the seconds of the last-member
query interval to separate the queries. When no response is received, the querier
stops forwarding multicast packets to the group on the particular interface.
3.1.3 IGMPV3
In the applications of the IGMPV1 and V2, there are the following defects:
Lack of efficient measures to control multicast sources
Difficult to establish the multicast path due to unknown multicast source
Difficult to find a unique multicast address. It is possible that multicast groups
are using the same multicast address.
On the basis of IGMPV1/V2, IGMPV3 provides an additional source filtering
multicast function. In IGMP V1/V2, the host determines to join a group and
receive the multicast traffic to the group address from any source only based on