Hi all,
I'm wondering how network switches work internally? My 8-port Netgear
RO318 router has a Broadcom 5317 8-port switch-on-a-chip. There is
only *one* ethernet controller in the device, integrated into the CPU.
In my newer Netgear WGT634U linux-based router, the switch, CPU, and
ethernet controller are all integrated into one IC.

My understanding is that in these unmanaged switches, the switching is
basically done by an ASIC that inspects the destination MAC address of
each packet and looks it up in a table of MAC<->port mappings. Does
each ethernet port on the switch have its own MAC and PHY, integrated
into the switch-on-a-chip IC? How does the switch build the table
associating MAC addresses to ports? Is there a limit to the size of
the table if there is a large hub-connected LAN segment on each port?

Are there any companies that actually release data sheets on their
switch-on-a-chip ICs? Broadcom is positively secret about their ICs it
seems: I can't find anything more than a 2-page brief on any of their
switch-on-a-chip products.

What about fancier managed switches, how do they work? Is the
switching still done by an ASIC, or is it done by a general-purpose CPU
such as in a home router?

Thanks for anyone who can clear up these confusions for me!

Dan Lenski
University of Maryland