User manual

Multicast Filtering
7278_en_01 PHOENIX CONTACT 5-3
IGMP Query
An LMS with activated query function actively transmits queries at intervals and evaluates
the received reports. The LMS only sends IGMP query reports if IGMP snooping is
enabled.
5.2.2.1 Multicast Registration with GMRP
GMRP is the GARP Multicast Registration Protocol and it allows the distribution of
Multicast Group Destination Addresses to layer two devices that don't support IGMP
Snooping. After a multicast participant has registered with the switch (e.g through an
IGMP report), the switch sends a GMRP broadcast packet to all GARP participating
switches with the Multicast Group Destination Address and whether the switch is joining or
leaving. This allows the other switches to create their own multicast groups and add the
receiving port to the group. By default GMRP is enabled when IGMP Snooping is enabled.
The receiving switches do not need to support IGMP Snooping to receive and understand
the GMRP packets they receive.