Allied-telesis AT-8326GB Manuel d'utilisateur télécharger pdf (Page 31)

AT-8326GB Installation Guide

The QoS feature was designed to address this problem. With it, Ethernet

frames can be assigned different priorities. The switch uses the priorities

when determining which frames to forward first. Frames from end-

nodes running time-critical applications can be given a high priority, so

that they will be forwarded by the switch ahead of less time-critical

frames.

IGMP Snooping The Internet Group Management Protocol (IGMP) enables routers to

create lists of nodes that want to receive multicast packets from a

multicast application. The router creates a multicast membership list by

periodically sending out queries to the local area networks connected to

its ports. A node wanting to become a member of a particular multicast

group responds to a query by sending a report. Nodes that join a

multicast group are referred to as host nodes.

Once the router has received a request from a host node to join a

multicast group, it notes the multicast group that the host node wants

to join and the port on the router where the node is located. Any

multicast packets belonging to that multicast group are then forwarded

by the router out the port. If a particular port on the router has no nodes

that want to be members of multicast groups, the router does not send

multicast packets out the port. This improves network performance by

restricting multicast packets only to router ports where host nodes are

located.

The IGMP snooping feature on the AT-8326GB switch enables the unit to

monitor the flow of queries from the router and reports from the host

nodes to build its own multicast membership lists. It uses the lists to

forward multicast packets only to switch ports where there are host

nodes that are members of multicast groups. This improves switch

performance and network security by further restricting the flow of

multicast packets only to those switch ports connected to host nodes.

Without IGMP snooping, the switch would flood all multicast packets

out all of its ports, except the port on which it received the packet. Such

flooding of packets can negatively impact switch and network

performance.

Note

By default, IGMP snooping is disabled on the switch.

Note

The AT-S41 software supports both IGMP version 1 and version 2.

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Allied-telesis AT-8326GB Manuel d'utilisateur Page 31