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xStack DES-3800 Series Layer 3 Stackable Fast Ethernet Managed Switch
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Timers
As previously mentioned, IGMPv3 incorporates filters to include or exclude sources. These filters are kept updated using timers.
IGMPv3 utilizes two types of timers, one for the group and one for the source. The purpose of the filter mode is to reduce the
reception state of a multicast group so that all members of the multicast group are satisfied. This filter mode is dependant on
membership reports and timers of the multicast group. These filters are used to maintain a list of multicast sources and groups of
multicast receivers that more accurately reflect the actual sources and receiving groups at any one time on the network.
Source timers are used to keep sources present and active within a multicast group on the Switch. These source timers are
refreshed if a group report packet is received by the Switch, which holds information pertaining to the active source group record
part of a report packet. If the filter mode is set to exclude, traffic is being denied from at least one specific source, yet other hosts
may be accepting traffic from the multicast group. If the group timer expires for the multicast group, the filter mode is changed to
include and other hosts can receive traffic from the source. If no group report packet is received and the filter mode is include, the
Switch presumes that traffic from the source is no longer wanted on the attached network and the source record list is then deleted
after all source timers expire. If there is no source list record in the multicast group, the multicast group will be deleted from the
Switch.
Timers are also used for IGMP version 1 and 2 members, which are a part of a multicast group when the Switch is running
IGMPv3. This timer is based on a host within the multicast group that is running IGMPv1 or v2. Receiving a group report from an
IGMPv1 or v2 host within the multicast group will refresh the timer and keep the v1 and/or v2 membership alive in v3.
NOTE: The length of time for all timers utilized in IGMPv3 can be determined using
IGMP configurations to perform the following calculation:
(Query Interval x Robustness Variable) + One Query Response Interval
IGMP Interface Settings
The Internet Group Multicasting Protocol (IGMP) can be configured on the Switch on a per-IP interface basis. To view the IGMP
Interface Table, click L3 Features > IP Multicast Routing Protocol > IGMP Interface Settings. Each IP interface configured
on the Switch is displayed in the below IGMP Interface Settings dialog box. To configure IGMP for a particular interface, click
the corresponding hyperlink for that IP interface. This will open another IGMP Interface Settings – Edit window:
Figure 8- 64. IGMP Interface Settings window
Figure 8- 65. IGMP Interface Settings – Edit window