Intel ZT8101 - Manual (Page 37)

ZT8101 User’s Manual 37
Switch Management and Operating Concepts
The ZT8101 switch supports both IGMPv1 and IGMPv2. You can select which version to use on a
particular VLAN.
IGMPv2 is an enhancement to the original IGMP and includes a few extensions such as a
procedure for the election of the multicast querier for each LAN, explicit leave messages for faster
pruning, and group-specific query messages.
IGMP Queriers
An IGMP querier sends IGMP Query packets periodically to help to maintain the multicast group
information for a VLAN. When IGMP Snooping is enabled for a VLAN, the switch uses the
following states to determine whether the VLAN becomes a querier:
• Non-Querier—Prevents the VLAN from becoming a querier.
• V1 Querier—Enables the sending of IGMPv1 query packets. If no querier is present in the
VLAN or the VLAN’s IP address is smaller than current V1 querier, the switch becomes the
querier for the VLAN. IGMPv2 group-specific query and leave packets are not handled.
• V2 Querier—If a V1 querier is present in the VLAN, the switch remains silent. If no querier
is present in the VLAN or the VLAN’s IP address is smaller than current V2 querier, the
switch becomes the querier for the VLAN. The switch then handles IGMPv2 group-specific
query and leave packets.
When receiving an IGMPv2 leave packet, the IGMP interface issues an IGMPv2 group specific
query packet immediately and waits one second to check if any IGMP reports are received on the
ports. If not, the port is removed from the IGMP group member list, and the group's multicast data
is not forwarded to this port until an IGMP report is received again.
If the IGMP interface is designated as the IGMP querier, the switch uses the following intervals for
sending query packets:
• When you enable IGMP snooping or boot the switch with the querier option enabled, the first
query packet will not be sent for 255 seconds. This time delay is non-standard.
• The second query packet will be sent after the Startup Querier Interval, which is one fourth of
the Query Interval. By default, this is 31 seconds.
• The next query packets will be sent periodically according to the Query Interval. The default
Query Interval is 125 seconds.
IGMP Snooping
IGMP Snooping is a feature that reduces the flooding of IP multicast traffic. The default behavior
for handling a multicast packet is to flood the packet to all members of a VLAN. With IGMP
Snooping, only the active member ports receive the data.
All groups learned by IGMP Snooping are recorded in an internal group table with the VLAN ID
and Multicast Group Address used as the table’s index. The table’s port list stores the active
member ports for this group. This table can contain a maximum of 128 groups. If the active
multicast groups exceed this limit, the new group’s data will be flooded in the VLAN.
You can globally enable or disable IGMP Snooping on the switch. You can also enable or disable
the snooping for a specific VLAN. You must enable IGMP globally for it to be enabled on a
specific VLAN. By default, the IGMP global flag is off and VLAN flag is on. Thus, when you
enable IGMP globally, it is enabled on all VLANs.