What is the max bandwidth of a L3 VLAN interface?

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Dec 27th, 2007
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I know this sounds strange, but I cant seem to find the exact max bandwidth of a L3 interface vlan of a 6509 switch with sup720 3blx. I am using an snmp based traffic monitor and it is picking up the default bandwidth of 1GB from the interface vlan interfaces and tripping alarms, because we push more than 1GB through the L3 interface. Anyone have the actual bandwidth that a vlan interface can sustain?


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jdean1 Thu, 12/27/2007 - 11:20
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Thanks. So are we saying there is no limit to the traffic a layer3 vlan interface can handle? I guess it would be the backplane limit? That seems too high though....hmm.. Does anyone have a detailed 6509 architecture diagram/doc?


Edison Ortiz Thu, 12/27/2007 - 11:36
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The bandwidth command is not a speed limiter. As explained before, the command is there as a parameter for dynamic routing protocols, QoS and NMS.

The value allowed in the command was described in the previous post.

More information regarding the command can be found on the link provided.

6500 Architecture can be found here:


johgill Sat, 01/05/2008 - 13:03
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There may be no easy answer here, but think of this scenario. Let's say you have to VLAN interfaces and you have one 10G port in switchport access in VLAN 1 and another 10G port in switchport access in VLAN 2.

If this switch just carries 10Gb/s from one port to another, and routes this traffic through hardware on the PFC, you are going to show 10Gb/s on those L3 interfaces.

We count those packets as hitting the respective interface, but as Edison noted, these are just abstractions and are limited only by the fabric itself. You could conceivably have many switchports in one VLAN and those numbers aggregate on the VLAN interface counters as something higher than any one interface can forward.

Technically, if you have software-switched traffic, let's say ICMP echo-requests destined for the VLAN interface IP address, you would get 1Gb/s max throughput since that is the connection from MSFC to supervisor.

Hope that helps!


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