SignaMax SC30010, Справочное руководство CLI

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Chapter 21
| Multicast Filtering Commands
IGMP Snooping
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Command Usage
◆
When a spanning tree topology change occurs, the multicast membership
information learned by the switch may be out of date. For example, a host
linked to one port before the topology change (TC) may be moved to
another port after the change. To ensure that multicast data is delivered to
all receivers, by default, a switch in a VLAN (with IGMP snooping enabled)
that receives a Bridge Protocol Data Unit (BPDU) with the TC bit set (by
the root bridge) will enter into “multicast flooding mode” for a period of time
until the topology has stabilized and the new locations of all multicast
receivers are learned.
◆
If a topology change notification (TCN) is received, and all the uplink ports
are subsequently deleted, a timeout mechanism is used to delete all of the
currently learned multicast channels.
◆
When a new uplink port starts up, the switch sends unsolicited reports for
all current learned channels out through the new uplink port.
◆ By default, the switch immediately enters into “multicast flooding mode”
when a spanning tree topology change occurs. In this mode, multicast
traffic will be flooded to all VLAN ports. If many ports have subscribed to
different multicast groups, flooding may cause excessive loading on the
link between the switch and the end host. Flooding may be disabled to
avoid this, causing multicast traffic to be delivered only to those ports on
which multicast group members have been learned.
◆ When the spanning tree topology changes, the root bridge sends a proxy
query to quickly re-learn the host membership/port relations for multicast
channels. The root bridge also sends an unsolicited Multicast Router
Discover (MRD) request to quickly locate the multicast routers in this
VLAN.
The proxy query and unsolicited MRD request are flooded to all VLAN ports
except for the receiving port when the switch receives such packets.
Example
The following example enables TCN flooding.
Console(config)#ip igmp snooping tcn-flood
Console(config)#