On Mon, 2006-01-30 at 08:21 -0600, Les Mikesell wrote: > On Mon, 2006-01-30 at 07:42, Claude Jones wrote: > > > > > > A switch or hub is simply a connection point on a single network. No > > > bridging or routing is involved. > > Here's where my knowledge tells me different. I thought a switch did do some > > simple routing. Doesn't a switch "remember" destinations that are on the > > local subnet, and build up tables, only routing signal through that are not > > destined for the local destination? > > The distinction is fuzzy because there are some expensive devices > called 'layer 3 switches' that understand IP addresses and can > do some routing and filtering based on them. However what is > normally called a switch works at the network layer 2, using > only ethernet MAC addresses. They learn the hardware addresses > of the connected devices as packets are sent from them and once > a destination is known they will only forward packets to that > destination out the correct port. However, they flood broadcast, > multicast, and unknown MAC destinations to all ports so the > filtering is transparent. They don't know anything about > IP addresses or subnets, though - this is all using the > hardware address built into every ethernet device. There are also certain types of hardware switches which can service more than one kind of network topology. They tend to share a common, very high-speed backplane and then use cards to handle one topology or another. These types of switches do something called translational bridging. You can *almost* think of this as routing at layer 2 because you get some of the benefits, including rebuilding packets based on topology, but you are still truly in the world of switching. Cheers, Chris -- ====================== "Never murder a man when he's busy committing suicide." -- Woodrow Wilson
