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Dimension ES-2008 Ethernet Switch
Filter and Security Setup 8-1
Chapter 8
Filter and Security Setup
This chapter shows you how to set IGMP and MAC filters and port security.
8.1 IGMP
Traditionally, IP packets are transmitted in one of either two ways -Unicast (1 sender to 1
recipient) or Broadcast (1 sender to everybody on the network). Multicast delivers IP
packets to just a group of hosts on the network.
IGMP (Internet Group Multicast Protocol) is a session-layer protocol used to establish
membership in a multicast group - it is not used to carry user data. Refer to RFC 1112 and
RFC 2236 for information on IGMP versions 1 and 2 respectively.
A layer-2 switch can passively snoop on IGMP Query, Report and Leave (IGMP version
2) packets transferred between IP multicast routers/switches and IP multicast hosts to
learn the IP multicast group membership. It checks IGMP packets passing through it,
picks out the group registration information, and configures multicasting accordingly.
Without IGMP snooping, multicast traffic is treated in the same manner as broadcast
traffic, that is, it is forwarded to all ports. With IGMP snooping, group multicast traffic is
only forwarded to ports that are members of that group. IGMP Snooping generates no
additional network traffic, allowing you to significantly reduce multicast traffic passing
through your switch.
For each attached network, an IGMP server periodically sends a query message to request
for group membership information. Hosts on the network that are members of a multicast
group send report messages back to the IGMP server. When a host leaves a group, it sends
a leave group message.
The following table describes the types of IGMP messages.
Table 8-1 IGMP Message Descriptions
TYPE DESCRIPTION
Query An IGMP server sends query messages asking for a response from each
host belonging to the multicast group.
Report A host sends report messages to the IGMP server to indicate that the host
wants to be or is a member of a given group indicated in the report
message.
Leave Group A host sends a leave group message to the IGMP server to indicate that the
host has terminated its membership of a specific multicast group.