TEG1210P 10-Port Gigabit Intelligent PoE Switch User Guide
- 51 -
RSTP bridge links; there is no need for ports to keep waiting until topology becomes
stable.
¾
IGMP Snooping
1. The implementation principle of IGMP Snooping
IGMP Snooping, run on data link layer is a multicast management scheme which works
on layer-2 switch to manage and control multicast group.
When a layer-2 Ethernet switch receives IGMP packets transmitted between hosts and
routers, the IGMP Snooping function starts analyzing the messages carried in the IGMP
packets. When snooping to learn that a host has sent an IGMP host report frame, the
switch will add this host to the corresponding multicast table; and when snooping to learn
that the host has sent an IGMP leave packet, it will delete the corresponding multicast
entry. Through continuously snooping on IGMP packets, the switch creates and
maintains a MAC multicast address table in layer-2 environment. And according to this
table, it forwards the multicast packets from routers.
2. The relation between IGMP Snooping and VLAN
VLAN technology, namely, virtual local area network, is introduced to switch for the main
purpose of restricting broadcast domain. To better combine the two to implement
multicast in VLAN environment, multicast groups created by IGMP Snooping should be
confined to VLAN broadcast domain. Thus, in the VLAN environment, not only the
transmission of multicast packets but also the transmission of IGMP control packets for
establishing multicast groups is confined to the VLAN. If a certain VLAN is deleted, then
all multicast groups previously created upon it will be deleted as well.
3. IGMP Snooping on Triple Standard IGMP Packets
IGMP Query Packets: These packets are sent by routers and consists of general query
and specific group query packets.
IGMP Report Packets: These packets are sent by hosts and generated when a host
actively wants to join a certain multicast group or responds to a router’s query. The switch,
TEG1210P, supports IGMP v1, IGMP v2 and IGMP v3 Report packets.
IGMP Leave Packets: Hosts running IGMP v1 will not send IGMP Leave packets when
leaving a multicast group. While hosts running IGMP v2 or IGMP v3 will send IGMP
