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Cat6509: Output Drops on Broadcast-Peaks

Unanswered Question
Feb 2nd, 2006
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Hi Guy´s,


I´ve a "litte" problem.


I´ve got a campus-wide VLAN with only broadcast-traffic in it. Avarage 8MBit/s. But sometimes there are Peaks,..with round about 40 - 50 MBit/s. At the moment when the peaks happen the number of Output-Drops on the Access-Ports increases. On every access-port in the vlan. Broadcast!! I´m talking about 20.000 output-drops per peak. When I put an traffic-generator in the VLAN, I get ca. 80MBit/s+ with only 30 drops in 60 seconds!!(no broadcast!)

Why will the broadcasts be dropped?


Hardware are 4 Cat6509 Sup720/3BXL an WS-X6748-GE-TX Modules. IOS is 12.2(18)SXE1. All ports are at fixed speed and duplex (100/full). No Broadcast Storm Controll or any pollicies. Servers are at fixed speed, too.


Hope one can help me!




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a-vazquez Wed, 02/08/2006 - 07:46
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Looking at your scenario, I would suggested you to implement " Excessive broadcast and unicast control" in your place.

this will filter unnecessary broadcast and also excess unknown unicast. The broadcasts are dropped in your scenario especially because of excessive broadcast.So, better suppress excess broadcast. The command is

(conf-if)#storm-control broadcast/multicast level

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