Thousands of hosts on a gigabit LAN, maybe not

Sameer Khosla skhosla at
Fri May 8 19:55:25 UTC 2015

You may want to look at CLOS / leaf/spine architecture.  This design tends to be optimized for east-west traffic, scales easily as bandwidth needs grow, and keeps thing simple, l2/l3 boundry on the ToR switch, L3 ECMP from leaf to spine.  Not a lot of complexity and scale fairly high on both leafs and spines.  


-----Original Message-----
From: NANOG [mailto:nanog-bounces at] On Behalf Of John Levine
Sent: Friday, May 08, 2015 2:53 PM
To: nanog at
Subject: Thousands of hosts on a gigabit LAN, maybe not

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


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