Siemens RUGGEDCOM ROX II User Manual page 462

Chapter 5
Setup and Configuration
When a switch transmits GMRP updates (from GMRP-enabled ports), all of the multicast groups known to the
switch, whether configured manually or learned dynamically through GMRP, are advertised to the rest of network.
As long as one host on the Layer 2 network has registered for a given multicast group, traffic from the
corresponding multicast source will be carried on the network. Traffic multicast by the source is only forwarded by
each switch in the network to those ports from which it has received join messages for the multicast group.
Leaving a Multicast Group
Periodically, the switch sends GMRP queries in the form of a leave all message. If a host (either a switch or
an end station) wishes to remain in a multicast group, it reasserts its group membership by responding with an
appropriate join request. Otherwise, it can either respond with a leave message or simply not respond at all. If the
switch receives a leave message or receives no response from the host for a timeout period, the switch removes
the host from the multicast group.
Notes About GMRP
Since GMRP is an application of GARP, transactions take place using the GARP protocol. GMRP defines the
following two Attribute Types:
• The Group Attribute Type, used to identify the values of group MAC addresses
• The Service Requirement Attribute Type, used to identify service requirements for the group
Service Requirement Attributes are used to change the receiving port's multicast filtering behavior to one of the
following:
• Forward All Multicast group traffic in the VLAN, or
• Forward All Unknown Traffic (Multicast Groups) for which there are no members registered in the device in a
VLAN
If GMRP is disabled on the RUGGEDCOM RX1500, GMRP packets received will be forwarded like any other
traffic. Otherwise, GMRP packets will be processed by the RUGGEDCOM RX1500, and not forwarded.
Example: Establishing Membership with GMRP
The following example illustrates how a network of hosts and switches can dynamically join two multicast groups
using GMRP.
In this scenario, there are two multicast sources, S1 and S2, multicasting to Multicast Groups 1 and 2,
respectively. A network of five switches, including one core switch (B), connects the sources to two hosts, H1 and
H2, which receive the multicast streams from S1 and S2, respectively.
424 GMRP (GARP Multicast Registration Protocol)
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