User`s manual

TN-5516/5518 Series Featured Functions
3-51
Query Mode
Query mode allows the TN-5500 to work as the Querier if it has the lowest IP address on the subnetwork to
which it belongs. IGMP querying is enabled by default on the TN-5500 to help prevent interoperability issues
with some multicast routers that may not follow the lowest IP address election method. Enable query mode to
run multicast sessions on a network that does not contain IGMP routers (or queriers).
NOTE TN-5500 is compatible with any device that conforms to the IGMP v2 and IGMP v3 device protocol.
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 filtering. IGMP works as follows:
1. 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.
2. 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.
3. When the report packet arrives at a port on a switch with IGMP Snooping enabled, the switch knows that the
port should forward traffic for the multicast group, and then proceeds to forward the packet to the router.
4. When the router receives the report packet, it registers that the LAN or VLAN requires traffic for the
multicast groups.
5. When the router forwards traffic for the multicast group to the LAN or VLAN, the switches only forward the
traffic to ports that received a report packet.
GMRP (GARP Multicast Registration Protocol)
The TN-5500 supports IEEE 802.1D-1998 GMRP (GARP Multicast Registration Protocol), which differs from
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 information dynamically. GMRP functions 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 forwarded from this port. When a port receives a GMRP-leave message, it will
de-register the multicast address from its database, and all the multicast packets with this multicast address
are not able to be forwarded from this port.
Static Multicast MAC
Some devices may only support multicast packets, but not support either IGMP Snooping or GMRP. The
TN-5500 supports adding multicast groups manually to enable multicast filtering.
Enabling Multicast Filtering
Use the serial console or Web interface to enable or disable IGMP Snooping and IGMP querying. If IGMP
Snooping is not enabled, then IP multicast traffic is always forwarded, flooding the network.
Configuring IGMP Snooping
IGMP Snooping provides the ability to prune multicast traffic so that it travels only to those end destinations
that require that traffic, thereby reducing the amount of traffic on the Ethernet LAN.