Designing an IPTV Network - Introduction for IGMP
Before we begin designing an IPTV Network, there are 3 important concepts of Zyxel’s IGMP (Internet Group Management Protocol) and IGMP Snooping that administrators should be aware of.
1. What are General Queries and Group Specific Queries?
General Query: The querier will send query messages to the multicast clients to learn which multicast groups still have active members within the network.
Group Specific Query: When the client leaves a multicast group and sends a leave group message, the querier will send this query message to learn if a particular group has any other active members on a downlink port.
2. What are IGMP Snooping Querier Modes?
There are 3 Querier Modes: Auto, Fixed and Edge.
Fixed: To have the Switch always use the port as an IGMP query port. Select this when you connect an IGMP multicast server to the port.
Edge: Prevents the switch from using the port as an IGMP query port. The Switch will not keep any record of an IGMP router being connected to this port. The switch does not forward IGMP join or leave packets to this port.
Auto: The port behaves as a Fixed port if the port receives any IGMP queries. The port behaves as an Edge port if the port receives no IGMP queries within a period of time.
3. What are the differences between IGMP Snooping fast/normal/immediate leave?
In fast leave mode, the switch itself sends out an IGMP Group-Specific Query (GSQ) message right after receiving an IGMP leave message from a host on a port. This determines whether other hosts connected to the port should remain in the specific multicast group. This helps speed up the leave process.
In normal leave mode, when the Switch receives an IGMP leave message from a host on a port, it forwards the message to the multicast router. The multicast router then sends out an IGMP Group-Specific Query (GSQ) message to determine whether other hosts connected to the port should remain in the specific multicast group. The switch forwards the query message to all hosts connected to the port and waits for IGMP reports from hosts to update the forwarding table.
Select this option to set the Switch to remove this port from the multicast tree once the ports receive an IGMP leave message. Select this option if there is only one host connected to this port.
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