Some people I know (yes really) are building a system that will have several thousand little computers in some racks. Each of the computers runs Linux and has a gigabit ethernet interface. It occurs to me that it is unlikely that I can buy an ethernet switch with thousands of ports, and even if I could, would I want a Linux system to have 10,000 entries or more in its ARP table.

Most of the traffic will be from one node to another, with considerably less to the outside. Physical distance shouldn't be a problem since everything's in the same room, maybe the same rack.

What's the rule of thumb for number of hosts per switch, cascaded switches vs. routers, and whatever else one needs to design a dense network like this? TIA

Brocade's Virtual Cluster Switching (VCS) fabric on their VDX switches is a good solution for large, flat data center networks like this. It's based on TRILL, so no STP or tree structure are required. All ports are live, as is all inter-switch bandwidth. Cisco has a similar solution, as do other vendors. Thank you, Jerry -- Jerry J. Anderson, CCIE #5000 Member, Anderson Consulting, LLC 800 Ridgeview Ave, Broomfield, CO  80020-6618 Office: 650-523-2132     Mobile: 773-793-7717 www.linkedin.com/in/AndersonConsultingLLC