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Forwarding bandwidth, is usually the capacity of the fabric. To avoid queuing traffic, you need 2x all your port "bandwidths". To provide sufficient PPS, for minimum size Ethernet, you need 1.488 Mpps per gig, for all your port bandwidths. (E.g. 24 [duplex] gig ports need 48 Gbps fabric bandwidth and 35.712 Mpps.)
Sometimes spec sheets will list higher values, than you need (or the device can use) but that's often because the same fabric and forwarding hardware might be used in a larger capacity device. For example, the difference between a 24 and 48 port device, internally, might only be the number of edge ports that connect to the "innards" of the device.
Current Enterprise class switches are often line rate or wire speed capable (i.e. they can run every port at full rate, concurrently). However that's not always true with older switches, e.g. 3560G.
