Avoiding Bottlenecks

It is especially important to not oversubscribe ports in a mirroring configuration because this can cause bottlenecks and will result in discarded traffic.

If, for example, there are 10 users in VLAN 1, each attached to a 10 Mbps port, when you mirrored VLAN 1 to another 10 Mbps port to which your sniffer is attached, the probe switch would probably have to drop packets at the destination port. Since your purpose in configuring mirroring is to see all of the traffic for VLAN 1, it would be better in this scenario to attach the sniffer to a 100 Mbps port.