User`s manual

Moxa Managed Ethernet Switch/Extender Featured Functions
3-50
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 configures its filters accordingly.
IGMP Snooping Enhanced Mode
Snooping Enhanced Mode allows your switch to forward multicast packets to the Moxa switch’s member port
only. If you disable Enhanced Mode, data streams will run to the querier port as well as the member port.
Query Mode
Query mode allows the Moxa switch to work as the Querier if it has the lowest IP address on the subnetwork to
which it belongs.
NOTE
IGMP Snooping Enhanced mode is only provided in Layer 2 switches.
IGMP querying is enabled by default on the Moxa 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. Moxa switches support IGMP snooping version 1, version 2
and version 3. Version 2 is compatible with version 1.The default 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 filtering. Moxa switches support IGMP version 1, 2 and 3. 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 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 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 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 specified sources.
IGMP version comparison
IGMP Version Main Features Reference
V1 a. Periodic query RFC-1112
V2 Compatible with V1 and adds:
a. Group-specific query
b. Leave group messages
c. Resends specific queries
to verify leave message was the last one in
the group
d. Querier election
RFC-2236
V3 Compatible with V1, V2 and adds:
a. Source filtering
- accept multicast traffic from specified source
- accept multicast traffic from any source except the specified source
RFC-3376