Digital Networks North America DNswitch 800 Benutzerhandbuch

DNswitch 800

Configuring and Monitoring the Switch  37

Multicasting is used to support real-time applications such as video 
conferencing or streaming audio. A multicast server does not have to 

establish a separate connection with each client. It merely broadcasts its 

service to the network, and any hosts which want to receive the multicast 
register with their local multicast switch/router. Although this approach 

reduces the network overhead required by a multicast server, the 

broadcast traffic must be carefully pruned at every multicast switch/router 
it passes through to ensure that traffic is only passed on the hosts which 

subscribed to this service.

This switch uses IGMP (Internet Group Management Protocol) to query 
for any attached hosts who want to receive a specific multicast service. 

The switch looks up the IP Multicast Group used for this service and adds 

any port which received a similar request to that group. It then propagates 
the service request on to any neighboring multicast switch/router to 

ensure that it will continue to receive the multicast service. (For more 

information, see “IP Multicast Filtering” in the DNswitch 800 Management 
Guide.)

This protocol allows a host to inform its local switch/router that it wants to 

receive transmissions addressed to a specific multicast address group. 
Use the IGMP Configuration screen to set key parameters for multicast 
filtering as shown below.

IGMP Status

If enabled, the switch will monitor network traffic to determine 
which hosts want to receive multicast traffic.

Act as IGMP 
Querier

If enabled, the switch can serve as the “querier,” which is 
responsible for asking hosts if they want to receive multicast 
traffic. (Not available for the current firmware release.)

IGMP Query Count

The maximum number of queries issued for which there has 
been no response before the switch takes action to solicit 
reports. (Range: 2 - 10.)

IGMP Report Delay

The time (in seconds) between receiving an IGMP Report for an 
IP multicast address on a port before the switch sends an IGMP 
Query out that port and removes the entry from its list. 
(Range: 5 - 30.)