Siemens RUGGEDCOM ROX II User Manual page 339

RUGGEDCOM ROX II
CLI User Guide
Section 8.4.1.2
GMRP (GARP Multicast Registration Protocol)
The GARP Multicast Registration Protocol (GMRP) is an application of the Generic Attribute Registration Protocol
(GARP) that provides a Layer 2 mechanism for managing multicast group memberships in a bridged Layer 2
network. It allows Ethernet switches and end stations to register and unregister membership in multicast groups
with other switches on a LAN, and for that information to be disseminated to all switches in the LAN that support
Extended Filtering Services.
GMRP is an industry-standard protocol first defined in IEEE 802.1D-1998 and extended in IEEE 802.1Q-2005. GARP
was defined in IEEE 802.1D-1998 and updated in 802.1D-2004.
NOTE
GMRP provides similar functionality at Layer 2 to what IGMP provides at Layer 3.
Joining a Multicast Group
In order to join a multicast group, an end station transmits a GMRP join message. The switch that receives the join
message adds the port through which the message was received to the multicast group specified in the message.
It then propagates the join message to all other hosts in the VLAN, one of which is expected to be the multicast
source.
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 RX5000, GMRP packets received will be forwarded like any other traffic.
Otherwise, GMRP packets will be processed by the RUGGEDCOM RX5000, and not forwarded.
GMRP (GARP Multicast Registration Protocol)
Chapter 8
Layer 2
293