3com S7906E Instruccion De Instalación

 

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A switch does not forward an IGMP report through a non-router port. This is because if the switch 

forwards a report message through a member port, all the attached hosts listening to the reported 

multicast address will suppress their own reports upon receiving this report according to the IGMP 

report suppression mechanism on them, and this will prevent the switch from knowing whether the 

reported multicast group still has active members attached to that port.  

For the IGMP report suppression mechanism on hosts, refer to IGMP Configuration in the IP Multicast 

Volume.  

 

When an IGMPv1 host leaves a multicast group, the host does not send an IGMP leave message, so 

the switch cannot know immediately that the host has left the multicast group. However, as the host 

stops sending IGMP reports as soon as it leaves a multicast group, the switch deletes the forwarding 

entry for the dynamic member port corresponding to the host from the forwarding table when its aging 

timer expires.  

When an IGMPv2 or IGMPv3 host leaves a multicast group, the host sends an IGMP leave message to 

the multicast router.  

When the switch receives an IGMP leave message on a dynamic member port, the switch first checks 

whether a forwarding table entry for the group address in the message exists, and, if one exists, 

whether the outgoing port list contains the port.  

z 

If the forwarding table entry does not exist or if the outgoing port list does not contain the port, the 

switch discards the IGMP leave message instead of forwarding it to any port. 

z 

If the forwarding table entry exists and the outgoing port list contains the port, the switch forwards 

the leave message to all router ports in the native VLAN. Because the switch does not know 

whether any other hosts attached to the port are still listening to that group address, the switch 

does not immediately remove the port from the outgoing port list of the forwarding table entry for 

that group; instead, it resets the aging timer for the port. 

Upon receiving the IGMP leave message from a host, the IGMP querier resolves the multicast group 

address in the message and sends an IGMP group-specific query to that multicast group through the 

port that received the leave message. Upon receiving the IGMP group-specific query, the switch 

forwards it through all its router ports in the VLAN and all member ports for that multicast group, and 

performs the following to the port on which it received the IGMP leave message:  

z 

If any IGMP report in response to the group-specific query is received on the port (suppose it is a 

dynamic member port) before its aging timer expires, this means that some host attached to the 

port is receiving or expecting to receive multicast data for that multicast group. The switch resets 

the aging timer of the port.  

z 

If no IGMP report in response to the group-specific query is received on the port before its aging 

timer expires, this means that no hosts attached to the port are still listening to that group address: 

the switch removes the port from the outgoing port list of the forwarding table entry for that 

multicast group when the aging timer expires.