Cabletron Systems SmartSTACK ETHERNET ELS10-27 User Manual page 82

Configuring Your SmartSTACK Ethernet ELS10-27
routing protocols to determine their location and adjust the Þlters
accordingly.
When subsequent queries are heard by the CPU, the CPU notes if any
response is heard for each group. A count is kept for each group
indicating the number of times a query was heard and there was no
response received. When the count reaches its maximum value of 5 the
group entry is modiÞed and packets for that group are only forwarded to
the CPU and to the query port. If an IGMPv2 speciÞc query is heard, this
is not counted as having received a general query. It only counts as a valid
query for that group.
If an IP Multicast/UDP packet is received by the CPU that has not had a
response issued for it, an entry is placed in the data base restricting
forwarding of those packets to just the CPU. The idea is, rather than place
entries in the data base for all unwanted entries, wait until trafÞc is heard
from the unwanted entries and then restrict it. The number of entries
should therefore be smaller, and based on how quickly the CPU can
respond, a limited amount of unwanted trafÞc will leak through initially.
This is known as Dynamic IP Multicast Þltering and the use of it is user
selectable. The default value for this selection is off. If, after creating this
dynamic Þlter, there is a response, the response port is added to the Þlter.
Once the response has been heard, if a querier is known, or is later heard
from, it too is added to the entry. This is done with both the presence and
absence of a querier.
If this feature is not selected (the default), a hardware Þlter is set to Þlter
out all IP Multicast packets that are UDP packets from being received by
the CPU.
You are also able to select whether you want the unit to act as an IGMP
querier. This feature is used in the absence of any other IGMP queriers on
the network.
Five commands are used to control the following functions:
¥ Enable/Disable IGMP Þltering - the default is enabled.
¥ Add/Delete a static IP Multicast Þlter on a group of ports.
¥ Enable/Disable Dynamic IP Multicast Þltering - the default is
disabled.
¥ Enable/Disable the unit to act as a querier - the default is disabled.
¥ Specify ports to be included in all Þlters (expected querier ports).
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