Operation Manual – Multicast Protocol
H3C S3610&S5510 Series Ethernet Switches
Chapter 5 IGMP Configuration
5-4
the router with the lowest IP address wins the querier election and all other
IGMPv2 routers become non-queriers.
3)
All the non-queriers start a timer, known as “other querier present timer”. If a router
receives an IGMP query from the querier before the timer expires, it resets this
timer; otherwise, it assumes the querier to have timed out and initiates a new
querier election process.
II. “Leave group” mechanism
In IGMPv1, when a host leaves a multicast group, it does not send any notification to
the multicast router. The multicast router relies on host response timeout to know
whether a group no longer has members. This adds to the leave latency.
In IGMPv2, on the other hand, when a host leaves a multicast group:
1)
This host sends a Leave Group message (often referred to as leave message) to
all routers (the destination address is 224.0.0.2) on the local subnet.
2) Upon receiving the leave message, the querier sends a configurable number of
group-specific queries to the group being left. The destination address field and
group address field of the message are both filled with the address of the multicast
group being queried.
3) One of the remaining members, if any on the subnet, of the group being queried
should send a membership report within the maximum response time set in the
query messages.
4) If the querier receives a membership report for the group within the maximum
response time, it will maintain the memberships of the group; otherwise, the
querier will assume that no hosts on the subnet are still interested in multicast
traffic to that group and will stop maintaining the memberships of the group.
5.1.4 Enhancements in IGMPv3
Built upon and being compatible with IGMPv1 and IGMPv2, IGMPv3 provides hosts
with enhanced control capabilities and provides enhancements of query and report
messages.
I. Enhancements in control capability of hosts
IGMPv3 has introduced source filtering modes (Include and Exclude), so that a host not
only can join a designated multicast group but also can specify to receive or reject
multicast data from a designated multicast source. When a host joins a multicast group:
z
If it needs to receive multicast data from specific sources like S1, S2, …, it sends a
report with the Filter-Mode denoted as “Include Sources (S1, S2, ……).
z
If it needs to reject multicast data from specific sources like S1, S2, …, it sends a
report with the Filter-Mode denoted as “Exclude Sources (S1, S2, ……).
As shown in
, the network comprises two multicast sources, Source 1 (S1)
and Source 2 (S2), both of which can send multicast data to multicast group G. Host B
