RuggedCom RS400 Benutzerhandbuch

Multicast Filtering 

 

 

ROS™  v3.5 

196 

RS400 

M1 

M2 

Membership Query 

M1 Membership Report 

Membership Query 

M2 Membership Report 

 

 

In this example the general membership query sent to the C1-C2 segment is answered by a 
membership report indicating the desire to subscribe to a stream M2. The router will forward the 
M2 stream onto the C1-C2 segment. In a similar fashion the router discovers that it must 
forward M1 onto segment C3-C4. 

A consumer may join any number of multicast groups, issuing a membership report for each 
group. Hosts on the segment note membership reports from other hosts and will suppress their 
own reports accordingly. In this way the IGMP protocol guarantees the segment will issue only 
one join for each group. 

The router periodically queries each of its segments, in order to determine if at least one 
consumer still subscribes to a given stream. If no responses occur within a given timeout period 
(usually about two query intervals) the router will prune the multicast stream from the given 
segment. 

A more usual method of pruning occurs when consumers wishing to unsubscribe issue an IGMP 
“leave group” message. The router will immediately issue a group-specific membership query to 
determine whether there are any remaining subscribers of that group on the segment. After the 
last consumer of a group has un-subscribed, the router will prune the multicast stream from the 
given segment. 

The IGMP Snooping feature provides a means for switches to snoop (i.e. watch) the operation 
of routers, respond with joins/leaves on the behalf of consumer ports and to prune multicast 
streams accordingly. 

There are two modes of IGMP the switch can be configured to assume, active and passive.  

Active Mode 

ROS

™ IGMP supports “routerless” mode of operation. 

When such a switch is used without a multicast router, it is able to function as if it is a 
multicast router sending IGMP general queries.