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Page 25 | AlliedWare™ OS How To Note: IGMP
IGMP proxy > Explanation of IGMP proxy
Switch
1
receives the proxied report from switch 3. Switch
1
notes that switch 3 is interested
in the group 224.
1
2.
1
3.
1
4 and sends the group multicast to switch 3 on port 49. Output of
the command show igmpsnooping shows the membership that switch
1
is aware of.
When a client leaves a group
When the client on switch 2 wants to stop receiving the group’s multicast stream, it sends an
IGMP Leave message. The switches use the above process to transfer the message to
switch 1.
Note the following points about how IGMP Proxy deals with Leave messages:
z The Proxy sends an IGMP Leave Group message via its upstream interface only when the
last interface on the Proxy leaves the group.
z The Proxy does not respond to IGMP Join or Leave Group messages received via its
upstream interface, but only to those received via downstream interfaces.
z The Proxy does respond to IGMP query messages received via its upstream interface.
When the Proxy—switch 3 in this example—sends a Leave Group message upstream, the
upstream IGMP Querier—switch
1
—sends a membership query. Switch 3 takes that
query and proxies it to the downstream interface, vlan
1
00, with its own IP as the source
(
1
72.3
1
.0.253). This means any other interested clients on switch 2 can declare their
interest in continuing to receive the multicast stream.
Manager Switch 1> show igmpsnooping
IGMP Snooping
------------------------------------------------------------------------
Status ........................... Enabled
Disabled All-groups ports ........ None
Vlan Name (vlan id) ..... default (1)
Group List ..............
No group memberships.
Vlan Name (vlan id) ..... vlan200 (200)
Group List ..............
Group. 224.12.13.14 Entry timeout 182 secs
Ports 49
------------------------------------------------------------------------