DHCP transactions per second

[Ian Anderson]

I am trying to do some stress testing on our dhcp servers (3.1.0b2) and  
am looking for anyone else who has had to do this, to offer up there 
thoughts.  I am currently trying to figure out what our current servers 
tps count is.

If I have 40,000 clients, those clients at any given time could be doing 
4-way transactions (DHCPDISCOVER/OFFER/REQUEST/ACK) or 2-way (RENEW/ACK).

With 40,000 clients each doing 4 transactions in 24 hours(DHCPDISCOVER), 
this computes to 160,000 transactions in 24 hours. If I divide that by 
86400 seconds this comes out to ~1.85 4-way transactions per second. 

However if the client is doing DHCPRENEW's this is a 2-way communication 
which lowers the transaction count.  Our lease times are set to 86400 
(24 hours)  So every 43200 seconds (12 hours) clients are going to do a 
DHCPRENEW/ACK. Using the same formula as above 40000 * 2 = 80000 
transactions in 12 hours. 80000 * 2 = 160000 2way transactions in 24 
hours. 160000/86400 = ~1.85 2-way transactions per second.

Both DHCPDISCOVER and DHCPREQUEST values compute to the same tps. Could 
one conclude that when attempting to compute dhcp tps, you only need to 
take DHCPDISCOVER 4 way handshakes into account?  

Math was never my strongest subject and I am hoping someone can offer 
advise as to wether or not this is the proper way to compute DHCP tps.  
I will be using a combination of the Ixia IXLoad test suite and 
Nominum's dhcperf tool to perform stress tests.   All advise is welcome.