Gmrp (Garp Multicast Registration Protocol) - Siemens RX1500 User Manual

RUGGEDCOM ROX II
User Guide
Assuming that router 1 is the querier for VLAN 2 and router 2 is simply a non-querier, the switch will periodically
receive queries from router 1 and maintain the information concerning which port links to the multicast router.
However, the switch port that links to router 2 must be manually configured as a router port. Otherwise, the switch
will send neither multicast streams nor joins/leaves to router 2.
Note that VLAN 3 does not have an external multicast router. The switch should be configured to operate in its
routerless mode and issue general membership queries as if it is the router.
• Processing Joins
If host C1 wants to subscribe to the multicast streams for both P1 and P2, it will generate two membership
reports. The membership report from C1 on VLAN 2 will cause the switch to immediately initiate its own
membership report to multicast router 1 (and to issue its own membership report as a response to queries).
The membership report from host C1 for VLAN 3 will cause the switch to immediately begin forwarding
multicast traffic from producer P2 to host C2.
• Processing Leaves
When host C1 decides to leave a multicast group, it will issue a leave request to the switch. The switch will
poll the port to determine if host C1 is the last member of the group on that port. If host C1 is the last (or only)
member, the group will immediately be pruned from the port.
Should host C1 leave the multicast group without issuing a leave group message and then fail to respond to a
general membership query, the switch will stop forwarding traffic after two queries.
When the last port in a multicast group leaves the group (or is aged-out), the switch will issue an IGMP leave
report to the router.
Section 5.25.1.2

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.
GMRP (GARP Multicast Registration Protocol)
Chapter 5
Setup and Configuration
567