The Internet Group Management Protocol (IGMP v1.0) is used by IP hosts to report their host group memberships to any immediately neighboring multicast routers. IGMP is an asymmetric protocol and is specified here from the point of view of a host, rather than a multicast router.

!IGMPv1 has no leave mechanism. If a host no longer wants to receive the traffic, it simply quits. If it is the last, the router will not have any answers to its query and will delete the

NOTE

GDA for that subnet.

For IGMP v2.0,

IGMP v2.0 allows group membership termination to be quickly reported to the routing protocol, which is important for high-bandwidth multicast groups and/or subnets with highly volatile group membership.

Multicast routers use IGMP v2.0 to learn which groups have members on each of their attached physical networks. A multicast router keeps a list of multicast group memberships for each attached network, and a timer for each membership. "Multicast group memberships" means the presence of at least one member of a multicast group on a given attached network, not a list of all of the members.

When a host receives a General Query, it sets delay timers for each group (excluding the all-systems group) of which it is a member on the interface from which it received the query.

When a router receives a Report, it adds the group being reported to the list of multicast group memberships on the network on which it received the Report and sets the timer for the membership to the [Group Membership Interval]. When a host joins a multicast group, it should immediately transmit an unsolicited Version 2 Membership Report for that group, in case it is the first member of that group on the network.

When a host leaves a multicast group, if it was the last host to reply to a Query with a Membership Report for that group, it should send a Leave Group message to the all-routers multicast group.

3.9 Stack

Stacking function is convenient for administrator to manage multiple switches by single IP. Basically, you

got to have min. 2 units.

Step 1: Linking the switches by one category 5 or fiber cable.

Step 2: Choose either one management switch as Master switch (ex: 192.168.100.128), enter it’s web interface.

Step 3: Choose “Stack Config”. There are four available options from the “Stacking State”. The options and descriptions are shown as below:

Disable: disable stack function.

Auto select: choose this stack mode. It will assign the Switch with minimum MAC address as the Master device.

Master: choose this stack mode. It allow assign one specific Switch as the Master device.

Slave: choose this stack mode. It allow assign one specific Switch as the Slave device. The stack config screen in Figure 3-9 appears.

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