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Managing Switches
Configuration
environment (where more than one IP network is configured in a single
broadcast domain).
See Routing Information Protocol.
Internet Group Management Protocol (IGMP)
Multimedia and email applications need the ability to communicate to
multiple destinations efficiently. IP multicasting allows hosts to dynamically
register for sending or receiving multicast traffic.
The Internet Group Management Protocol is a method for automatically
controlling multicast traffic through the network. Using multicasting,
applications can send one copy of a packet addressed to a group of
computers that wish to receive it. This method is more efficient than sending
a separate copy to each node. Other advantages of multicasting include:
■ information delivered in a timely, synchronized manner because all desti-
nation nodes receive the same packet
■ information can be sent to destinations whose addresses are unknown
■ reduces the number of packets on the network because only one multicast
packet is sent.
IGMP uses multicast queriers and hosts that support IGMP to manage
multicast traffic on the network. It specifies how the host informs the
network that it is a member of a multicast group. A set of queriers and hosts
that send and receive data from the same set of sources is a multicast group.
The HP switches have a standards-based IGMP implementation. The
switches process IGMP packets by learning which of the switch’s interfaces
are linked to hosts that are members of multicast groups and multicast
routers. It limits multicast traffic by monitoring the IGMP traffic to learn
which hosts are in which multicast groups, then allowing IP multicast traffic
to be sent only to ports with valid host group members.
When a switch receives an IGMP packet, it updates the internal IP multicast
forwarding table with the IGMP membership read from that packet. The
switch then sends the packet to the ports with members of the destination
multicast group.
Special multicast routers/queriers communicate by using three message
types - query, report, and leave group. The query message, sent by a querier,
is used to discover which network interfaces belong to a multicast group.
Each host responds to the query message with a report message that tells the
querier the host is a member of the multicast group. The host also can send a
report message to join a group or a leave message to leave a group.
Managing Switches
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