How many connections can nginx handle?

[arnoldguo]

I have a server running proxy_pass the http request(mainly GET,html,jpg
etc.) to backend server(20+ server running nginx cache).
this server with 32 core CPU,64G RAM,2X 10G NIC,RHEL 6.3,backend server with
1000M NIC.
When the load raise to 300k connections,3Gbps network traffic,new connection
can not be serviced,cannot connect to nginx's port,but the system load is
low(~1.00),and has many free memory,
no errorlog in /var/log/message,has some nginx errorlog like"upstream timed
out to backend server",
but the backend's service is normal,load is not hight...
i have tune  tcp config,can handle 2000K conn,it seems that nginx cannot
handle so much connection?

nginx config:
worker_processes 32;use worker_cpu_affinity;
keepalive 32 to backend servers,
proxy_buffering on or off has the same result...

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,232623,232623#msg-232623