Buffer/Queue size

Unanswered Question
Jul 24th, 2007

In my QoS-implemantation i can configure buffer size for different ingress- and egress-queues. I?ve to know, how much memory is used for these queues. I?ve only found a whitepaper for 6500.

("Buffers, Queues & Thresholds on Catalyst 6500 Ethernet Modules")

I?m loooking for information about 3750 and 4500.

Are there any similar papers?

Thanks and Best Regards


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Pavel Bykov Wed, 07/25/2007 - 22:24

What exactly are you asking? The size of the software queue? or how much KB of DRAM does one buffer takes?

a.konnemann Wed, 07/25/2007 - 22:53

i think its coherent. I like to know the size of the buffer and how much kB from the buffer are dedicated to the several queues.

agugger Tue, 07/31/2007 - 00:38


The Catalyst 6500 and 4500 has different design. The 6500 has all hardware related buffers on his line modules. Each type of line modules has own intelligence and functionalities. Depend the mix of Supervisors and modules you have different capabilities. Top Sup720 and line modules 67xx come up to 80 Gigabit per slot. The other end are Sup1 and Sup2 without switch fabric and with line modules 61xx-63xx has only 4x8gigabit channels common for all slots on the chassis.

The 4500 has a shared memory as central switching instance. The line cards are just interfaces without any intelligence. All intelligence and functionalities are done by the supervisor. Each line card is via 6 channels 1gigabit of each connected to the supervisors. Depend the line cards you have different rates of oversubscriptions from 1:1 (4506) up to 8:1 (4x48). More information you will found in the following sheet:

Cisco Catalyst 4500 Series Line Cards Data Sheet


Table 1. Port Information for Line Cards, see the column wire rate

General QoS information can be fond at:

Configuring Quality of Service

Catalyst 4500 Series Switch Cisco IOS Software Configuration Guide, 12.2(37)S


Configuring QoS

Catalyst 3750 Switch Software Configuration Guide, 12.2(37)S




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