Cisco IE-3000-8TC User Manual

25-5
Cisco IE 3000 Switch Software Configuration Guide
OL-13018-03
Chapter 25 Configuring IGMP Snooping and MVR
Understanding IGMP Snooping
Leaving a Multicast Group
The router sends periodic multicast general queries, and the switch forwards these queries through all
ports in the VLAN. Interested hosts respond to the queries. If at least one host in the VLAN wishes to
receive multicast traffic, the router continues forwarding the multicast traffic to the VLAN. The switch
forwards multicast group traffic only to those hosts listed in the forwarding table for that IP multicast
group maintained by IGMP snooping.
When hosts want to leave a multicast group, they can silently leave, or they can send a leave message.
When the switch receives a leave message from a host, it sends a group-specific query to learn if any
other devices connected to that interface are interested in traffic for the specific multicast group. The
switch then updates the forwarding table for that MAC group so that only those hosts interested in
receiving multicast traffic for the group are listed in the forwarding table. If the router receives no reports
from a VLAN, it removes the group for the VLAN from its IGMP cache.
Immediate Leave
Immediate Leave is only supported on IGMP Version 2 hosts.
The switch uses IGMP snooping Immediate Leave to remove from the forwarding table an interface that
sends a leave message without the switch sending group-specific queries to the interface. The VLAN
interface is pruned from the multicast tree for the multicast group specified in the original leave message.
Immediate Leave ensures optimal bandwidth management for all hosts on a switched network, even
when multiple multicast groups are simultaneously in use.
Note You should only use the Immediate Leave feature on VLANs where a single host is connected to each
port. If Immediate Leave is enabled in VLANs where more than one host is connected to a port, some
hosts might inadvertently be dropped.
For configuration steps, see the “Enabling IGMP Immediate Leave” section on page 25-10.
IGMP Configurable-Leave Timer
You can configure the time that the switch waits after sending a group-specific query to determine if
hosts are still interested in a specific multicast group. The IGMP leave response time can be configured
from 100 to
5000 milliseconds. The timer can be set either globally or on a per-VLAN basis. The VLAN
configuration of the leave time overrides the global configuration.
For configuration steps, see the “Configuring the IGMP Leave Timer” section on page 25-10.

Cisco IE-3000-8TC Specifications

General

Switching Capacity	16 Gbps
MAC Address Table Size	8000
Uplink Ports	2 x 10/100/1000Base-T or SFP (Small Form-Factor Pluggable)
Operating Temperature	-40°C to 70°C
Mounting	DIN rail
Ports	8 x Ethernet 10/100Base-TX ports
Jumbo Frame Support	Yes