What is the difference between Switch Fabric Capacity and Forwarding Rate of a switch?

Also, what other types of speed or bandwidth are there for switching?

Here's the image from Dell N2000 series Switches comparison

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What is the difference between Switch Fabric Capacity and Forwarding Rate of a switch?

Switch Fabric Capacity: It usually means the maximum rate the hardware can move information between cards/ports. However it does not account for time spent looking up output port for frames and packets, for instance.

Forwarding Rate: It usually means the maximum rate the system can actually perform full forwarding for frames/packets, including delays with store-and-forward, MAC/route table lookup, and so on.

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Remember that what you are looking at is marketing material.

The Switch Fabric Capacity is listed in bits per second (bps) and is usually double what it really does since the vendors count full duplex.

The Forwarding Rate is measured in packets per second (pps) and is based on an arbitrary packet size which make the vendor look good.

You really need to dig into each switch individually to uncover the dirt. For instance, I know of a particular switch which has respectable backplane numbers, but when you look at the 10 Gb line cards, each three ports use a single ASIC which is only capable of 12 Gbps. You would need to use one 10 Gb SFP+ and two 1 Gb SFPs on a single ASIC to use it without lost frames.

This is a question for which the answer depends on the make and model of the switch.

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  • 1
    And a port capable of 10G doesn't guarantee it can deliver a single stream of 10gbps depending on the size of the VOQ – sdaffa23fdsf Feb 11 '16 at 16:10

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