A Switch for All Speeds

A Switch for All Speeds

LAN switches use logic that relies on information in the Ethernet header. Because all the more advanced forms of Ethernet use the same header, switch forwarding and learning logic do not change based on what speed Ethernet is used. The switch can behave the same way as always, with some ports using Ethernet, some Fast Ethernet, some Gigabit Ethernet, and so on.

Imagine that you want to support a bunch of users on a building floor, some with NICs that only support 10 Mbps 802.3, and some that only support 100 Mbps 802.3u Fast Ethernet. You might buy a switch that has 24 ports12 10-Mbps ports and 12 100-Mbps ports. Figure 6-12 shows the basic setup, with Fred using a 10-Mbps NIC and Wilma using a 100-Mbps NIC.