Explanation Of Igmp Snooping - Allied Telesis AR400 Series How To Configure

Explanation of
This section steps through the events that occur in a typical use of multicasting in this
network: to stream multicast packets for a group.
IGMP The following figure shows the process by which IGMP tracks multicast clients and ensures
learning that the correct clients receive the stream.
process
What happens before a multicast client exists:
1. Querier starts receiving multicast stream
2. Querier sends General Query (GQ)
3. Snooper 1 forwards Query out all ports.
What happens when a client joins a multicast group:
4. Client joins group by sending Membership
5. Snooper 1 receives Report on port 3,
6. Querier receives Report on port 49
7. Snooper 1 receives multicast stream
8. Querier continues to send
Page 11 | AlliedWare™ OS How To Note: IGMP
IGMP snooping
from server. Querier has no interested
clients so doesn't forward multicast.
to find out if any would-be clients exist.
Snooper 1 receives Query on port 26,
snoops Query, and creates All Groups
entry for port 26.
No clients exist, so no clients reply to
Query.
Report to the group address.
snoops Report, and adds a group entry
for port 3. Snooper 1 forwards Report
out its All Groups port.
and adds a group entry for port 49.
Querier starts forwarding multicast
stream out port 49.
and forwards it out port 3.
General Queries periodically.
These keep All Groups entries
alive on Snoopers.
IGMP snooping > Explanation of IGMP snooping
49
Multicast
Blocked
Querier
by STP
Multicast
server
49
Multicast
Querier
49
Multicast
Querier
49
Multicast
Querier
49
Multicast
Querier
49
Multicast
Querier
49
Multicast
Querier
GQ
49
Multicast
Querier
26
3
Snooper 2 Snooper 1
GQ
26
3
Snooper 1
26
GQ
3
Snooper 1
26
Report
3
Snooper 1
Report
26
3
Snooper 1
Multicast
26
3
Snooper 1
Multicast
26
Multicast
3
Snooper 1
Multicast
26
Multicast
3
Snooper 1
Pontential
client
GQ
Client
igmp-join.eps