Dell PowerConnect 5316M Manuale rapido - Pagina 3

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network and communications

as network complexity increases,

administrators require advanced

management options to help ensure

quality and efficiency.

Scheduling services the queues based on their configured priorities.

Queues can be configured in one of two ways:

•

Strict priority (SP): SP helps ensure that the highest-priority queues

are serviced first and that critical, time-sensitive traffic is prioritized

over less critical or less time-sensitive traffic.

•

Weighted round robin (WRR): WRR helps ensure that a single high-

priority application does not take over all bandwidth by allocating

queues proportionally to their assigned weights.

Figure 3 shows the QoS Global Queue Settings screen in the Dell

OpenManage Switch Administrator GUI for the PowerConnect 5316M. The

SP and WRR settings apply to all ports for egress traffic.

Snooping with Internet Group Management Protocol

IGMP is the standard protocol for IP multicasting in a broadcast domain.

Multicast groups are segregated host groups that share packets among

themselves; multicast datagrams are transmitted only to multicast group

members. The router maintains group membership lists through IGMP:

for example, a host joining a group sends an IGMP join message to the

router, or, alternatively, the switch forwards IGMP queries from the router

Figure 3.

QoS Global Queue Settings screen for the Dell PowerConnect

5316M switch

DELL POWER SOLUTIONS |

May 2007

Figure 4.

IGMP Snooping screen for the Dell PowerConnect 5316M switch

to all the ports connected to it. The advantage of the latter scheme is that

it allows a single copy to be sent to the switch, which then creates copies

and transmits them. By default, a Layer 2 switch handles IP multicast

traffic in the same manner as broadcast traffic, by forwarding it to all

interfaces. Thus, IGMP traffic can potentially flood the interfaces and

cause network congestion.

Layer 2 switches can use a feature called IGMP snooping to help pre-

vent this flooding. With this feature enabled, the switching application-

specific integrated circuit (ASIC) forwards all IGMP packets to the switch

processor, which then analyzes the incoming packets, maps the ports to

multicast groups, and determines which ports will send out the IGMP

queries and which routing protocols to use. This method uses a multicast

filtering database; the switch checks this database and only forwards

multicast datagrams to member interfaces, helping optimize interface

and bandwidth usage.

To use this feature on the PowerConnect 5316M, administrators must

enable both the bridge multicast filtering feature and IGMP snooping.

They can do this in the Dell OpenManage Switch Administrator GUI from

the Multicast Global Parameters screen and the IGMP Snooping screen

(see Figure 4), or by using the following commands:

console(config)# bridge multicast filtering

console(config)# ip igmp snooping

Removing hosts from groups requires updating the filtering database,

which can be done immediately upon receiving an IGMP leave command

or after a set leave time-out period. Administrators can configure this

setting from the IGMP Snooping screen or with the following command

(where setting is either time-out or immediate-leave):

console(config-if)# ip igmp snooping

leave-time-out setting