Informations about Switching bandwidth and Forwarding bandwidth

[taonrez]

Hello Team

In the specifications of Cisco switches, we find the following specifications: Switching bandwidth and Forwarding bandwidth

Please, I would like to have detailed explanations concerning these specifications and I would also like to know how to calculate their values.

Thank you in advance for your answer.

[Joseph W. Doherty]

Would need to see a specific example of the usage of the two terms to identify how they are being used, but I would "guess" switching bandwidth might be the switch's fabric bandwidth while forwarding bandwidth might be related to switch's PPS (packets per second) capacity.

Ideally, a switch has a fabric and PPS that can support all its ports at wire-speed/line-rate; and with modern (Enterprise) switches, this is often the case.  Older switches often could not support all their ports, concurrently, at wire-speed/line-rate either having an inadequate fabric bandwidth and/or PPS capacity.  (E.g. compare the older 48 port 3750G with the 4948.)

BTW, for modern switches, one or both switch fabric and/or PPS might exceed the needs of all the switch's ports (this happens, I believe, because modern switches might have hardware components, built-in, with a larger capacity than a particular switch model needs - e.g. a 24 vs. 48 port switch within the same family, the 24 port model might have the same fabric and PPS capacity as the 48 port model).

Also BTW, for an example, wire-speed/line-rate, for an 8 gig (duplex) port switch would need a 16 Gbps fabric (2x ports bandwidths) and (about)11.9 MPPS (for minimum size standard Ethernet - 8x 1.488 MPPS).  Anything less for fabric bandwidth and/or PPS could preclude all ports, concurrently, running at wire-speed/line-rate.  Anything more for fabric bandwidth and/or PPS wouldn't be utilized.

[taonrez]

This informations is from the datasheet Cisco Catalyst 2960X-24PS-L. And we have this specifications:

 Forwarding Bandwidth:108Gbps; Switching Bandwidth: 216Gbps.

I want to know how to calculate their values.

[Joseph W. Doherty]

"I want to know how to calculate their values."

Again, "switching" bandwidth, is likely fabric's bandwidth capacity and "forwarding" bandwidth is likely switch's PPS capacity (converted into bandwidth).

Generally, ideally (in Cisco specs), "switching" bandwidth will be 2x "forwarding" bandwidth.  Also, ideally, forwarding bandwidth would be the total aggregate of all the ports' bandwidth.

Again, in my example of an eight gig port switch, "forwarding" bandwidth should be 8 Gbps and "switching" bandwidth 16 Gbps.

Now, for some "gotchas", first switches like the 2960 might have stacking ports, which the spec sheet's specs either allow for in the forwarding and switching bandwidths.

Second, as forwarding bandwidth depends on PPS times frame size, for that spec, ideally vendor should note if forwarding bandwidth is supported for ALL frame sizes.  (In the past, forwarding bandwidth's maximum value might only have been supported with maximum size frames.  Smaller frames, to achieve the same bandwidth, require a higher PPS rate.)