Moxa Managed Ethernet Switch (UI_2.0_FW_5.x) User Manual
IGMP querying is enabled by def ault on the Moxa switch to ensure that query election is activated. Enable
query mode to run multicast sessions on a network that does not contain IGMP routers (or queriers). Query
mode allows users to enable IGMP snooping by VLAN ID. Moxa switches support IGMP snooping version 1,
version 2, and version 3. Version 2 is compatible with version 1.The def ault setting is IGMP V1/V2.
NOTE
Moxa Layer 3 switches are compatible with any device that conforms to the IGMP v2 and IGMP v3 device
protocols. Layer 2 switches only support IGMP v1/v2.
IGMP Multicast Filtering
IGMP is used by IP-supporting network devices to register hosts with multicast groups. It can be used on all
LANs and VLANs that contain a multicast capable IP router, and on other network devices that support
multicast f iltering. Moxa switches support IGMP version 1, 2 and 3. IGMP version 1 and 2 work as f ollows:
• The IP router (or querier) periodically sends query packets to all end-stations on the LANs or VLANs that
are connected to it. For networks with more than one IP router, the router with the lowest IP address is
the querier. A switch with IP address lower than the IP address of any other IGMP queriers connected to
the LAN or VLAN can become the IGMP querier.
• When an IP host receives a query packet, it sends a report packet back that identifies the multicast
group that the end-station would like to join.
• When the report packet arrives at a port on a switch with IGMP Snooping enabled, the switch knows
that the port should f orward traf f ic f or the multicast group, and then proceeds to f orward the packet to
the router.
• When the router receives the report packet, it registers that the LAN or VLAN requires traffic for the
multicast groups.
• When the router f orwards traf f ic f or the multicast group to the LAN or VLAN, the switches only f orward
the traf f ic to ports that received a report packet.
IGMP version 3 supports “source filtering,” which allows the system to define how to treat packets from
specified source addresses. The system can either white-list or black-list specif ied sources.
IGMP version comparison
V2
Compatible with V1 and adds:
1. Group-specific query
2. Leave group messages
3. Resends specific queries to verify leave message was the last one
in the group
RFC-2236
V3
Compatible with V1, V2, and adds:
Source f iltering
• accept multicast traffic from specified source
•
accept multicast traffic from any source except the specified source
RFC-3376
GMRP (GARP Multicast Registration Protocol)
Moxa switches support IEEE 802.1D-1998 GMRP (GARP Multicast Registration Protocol), which is dif f erent
f rom IGMP (Internet Group Management Protocol). GMRP is a MAC-based multicast management protocol,
whereas IGMP is IP-based. GMRP provides a mechanism that allows bridges and end stations to register or
de-register Group membership inf ormation dynamically. GMRP f unctions similarly to GVRP, except that
GMRP registers multicast addresses on ports. When a port receives a GMRP-join message, it will register
the multicast address to its database if the multicast address is not registered, and all the multicast packets
with that multicast address are able to be f orwarded f rom this port. When a port receives a GMRP-leave
message, it will de-register the multicast address f rom its database, and all the multicast packets with this
multicast address will not be able to be f orwarded from this port.
Static Multicast MAC
Some devices may only support multicast packets, but not support either IGMP Snooping or GMRP. The
Moxa switch supports adding multicast groups manually to enable multicast f iltering.
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