User Documentation

User Manual Managed Switches
98
Snooping Mode
Snooping Mode allows your switch to forward multicast packets only to the appropriate ports. The
switch "snoops" on exchanges between hosts and an IGMP device, such as a router, to find those
ports that want to join a multicast group, and then configure its filters accordingly.
IGMP Snooping Enhanced Mode
Snooping Enhanced Mode allows your switch to forward multicast packets to the Weidmüller switch
member port only. If you disable Enhanced Mode, data streams will run to the querier port as well as
the member port.
Querier Mode
Querier mode allows the Weidmüller switch 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 switch 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).
IGMP querying is enabled by default on the Weidmüller switch to ensure proceeding query election.
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. Weidmüller switches
support IGMP snooping version 1 and version 2. Version 2 is compatible with version 1.The default
setting is 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 filtering. Weidmüller switches support IGMP version 1 and 2. IGMP
version 1 and 2 work as follows:
• 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 querier 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 forward traffic for the multicast group, and then proceeds to forward 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 forwards traffic for the multicast group to the LAN or VLAN, the switches only
forward the traffic to ports that received a report packet.
IGMP version comparison